Kurdistan Regional Government Ministry of Higher Education and Scientific Research University of Sulaimani College of Education Department of Physics
PREPARATION AND CHARACTERIZATION OF Ho3+:TiO2 LASER ACTIVE MEDIUM USING SOL-GEL TECHNIQUE
A thesis Submitted to the Council of College of Education at the University of Sulaimani in partial fulfillment of the requirements for the degree of Master of Science in Physics (Laser)
By
Gashaw Kamal Arif B.Sc. in physics (2011), University of Sulaimani
Supervised by
Dr. Majida Ali Ameen Al-Zangana Assistant Professor
May
Gulan
2017
2717
This Thesis is Dedicated to:
My Respectful and Honest Parents, My Dear Sister and Brother, My Supervisor.
Gashaw
ACKNOWLEDGMENTS Foremost, I wish to express deep thanks to “Merciful Allah” for giving me enough strength and ability to complete this study successfully. Without the faith in the Almighty, I could not be able succeed. I would like to express my appreciation and deepest gratitude to my supervisor, Dr. Majida Ali Ameen Al-Zangana, for her inspiring academic guidance, constructive comments, and valuable suggestion throughout this research. She did not only support me academically, also she helped me broaden my point of view in life with her advice. My truthful thanks are to the council of college of Education/ University of Sulaimani for giving permission to me for undertaking this thesis. I express my sincere thanks to the Department of Physics at College of Education, especially the head of the department Dr. Ari Karim Ahmed, for his help and support during this study. A great respect and thanks to Dr.Asma Jawad Kadhim for her assistance in measuring (XRD-patterns, absorption and fluorescence emission spectra) of the samples. Sincere thanks are extended to Dr. Muhammad Alwan Hamza for his help. Best thanks for Mr. Muhammad Ahmed Saeed, Mr. Peshawa Omer Ameen, and Mr. Idrees Karim Muhammad for their continuous help in troubleshooting experimental setup. I am deeply grateful to all staff of the department of chemistry, especially the head of the department Dr.Karim Jumaah Jibrael for permitting me to work in their laboratory for some experimental part of this study. I would also like to thank Dr. Shujahadeen Bakr Aziz, Dr. Dler Rafeeq Sabr, and Dr. Omed Ghareeb Abdulla for their great help.
i
Special gratefulness to Mr. Qasim Fawzi Ahmed, Mr. Shwan Rasool Ahmed, Mrs. Renas Qasim Muhammad, Mr. Nawras hamid, and Mr.Jamal wahid for their valuable help. Sincere appreciation to Dr.Badeaa Ibrahim Abdulkareem, Dr.Eman Ibrahim Abdulkareem, Dr. Eman Dhahir Arif, Dr. Heshu Sulaiman Rahman, Dr. Hemn Hassan Othman, and Dr. Saddon Taha Ahmed for their immense assistance. Last but not least, my truthful indebtedness and Special thanks to my parents for their continuous encouragement and fundamental moral support throughout this work. All my thanks are not enough to repay my debt to you.
Gashaw
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ABSTRACT In this study, the sol-gel method was used for the preparation of pure and holmium (Ho3+) doped TiO2 solid lasing material, with different concentrations (1, 3, 5, and 7) wt% of Ho3+ ions and the best molar ratio (1: 1: 10: 0.1) of initial raw materials (TTIP: H2O: EtOH: HCl). The prepared samples were analyzed via: X-Ray Diffractometer (XRD), Fourier
Transform
Infrared
Spectrometer
(FTIR),
(UV/Vis)
Spectrophotometer, and Spectrofluorophotometer. Results of XRD pattern of pure and Ho3+ doped TiO2 nanopowder (after calcination at (500C for 1h)) showed that samples had anatase crystalline structure which represented by (101), (004), (200), (105), (211), (204), (116), (220), and (215) diffraction peaks. There was no appeared peak in XRD patterns of the doped samples related to Ho3+ ions, this due to the dopant concentration which was relatively low for XRDdevice to reveal. Also, from the XRD analysis and the use of the peak positions (2) of the anatase (101) and (200) reflection, lattice constants of the tetragonal anatase phase of TiO2 nanopowder had been calculated representing by 'a' and 'c'. Results showed that with increasing the dopant concentration; there was no notable change in the value of 'a', with a random change in the value of 'c'; this suggests that the dopant went into substitutional sites of Ti4+ in the TiO2 crystal structure. Basing on the full width at half maximum (FWHM) of the (101) anatase peak, grain size of both pure and doped samples were calculated, no systematical change in their values obtained by increasing the dopant concentration for the same mentioned reason. FTIR Spectrometer had been used to probe the structure of the prepared samples; the obtained spectra showed the presence of the titania bonds (Ti-O-Ti) and (Ti-O) in both pure and Ho3+ doped samples. Also, iii
in the doped samples spectra, bands around (1338, and 1339) cm-1 belongs to (3, 5, and 7) wt% dopant concentrations, while there was no observed band related to low concentration of 1wt% Ho3+ ions, that may not be enough to be detected by the testing device. Several attempts were carried out to measure the fluorescence spectra of the prepared samples. The recorded absorption spectra showed that, there was no any peak in the resulted absorption spectra of pure sample in spectral range (400-800) nm; this showed that pure TiO2 did not have absorption in the visible region. While three obvious absorption bands can be observed in the spectra of the doped samples, exactly at (450, 539, and 644) nm corresponding to (5I8→5F1,5G6), (5I8→5S2,5F4), and (5I8→5F5) transitions respectively for (3, 5, and 7) wt% dopant concentrations, at 1 wt% dopant concentration, there was no absorption bands at 450 and 539 nm, this might be due to not exciting this small amount of Ho3+ ions to upper levels at these two wavelengths. Results showed that upon 450 nm pumping wavelength to the doped samples, different fluorescence emission spectra were obtained in visible range corresponding to (5F4, 5S2→5I8) and (5F3→5I8) transitions. For 539 nm pumping; there was no any emission spectrum due to resonance fluorescence process. Via 644 nm pumping, different emission peaks had been obtained in UV/Vis regions which may belongs to upconversion transitions. Resulted fluorescence emission spectra of Ho3+ doped TiO2 samples gave an acceptable indication in the direction of preparation of laser active medium.
iv
CONTENTS
Acknowledgements ……………………………………………………....... i Abstract ………………………………………….……………………....... iii Contents ………………………………………………………………........ v List of Tables………………………………………………………………. ix List of Figures……………………………………………………………… x List of Symbols……………………………………………..…………..… xiii List of Abbreviations ……………………………………………………. xvi Thesis Organization …….………………………………………………. xvii
Chapter 1: Introduction 1.1 Introduction ……………………………………………………………. 1 1.2 Thesis Objectives …………………...………..…………………………. 3 1.3 Literature Survey……………………………..…………………….…… 3 1.3.1 Pure TiO2 Preparation ………………………..…………………….… 3 1.3.2 Rare Earth Doped TiO2 Preparation…………………………………... 7
Chapter 2: Theoritical Background 2.1 Introduction……………….…………………………………….……... 12 2.2 Fundamental of Sol-Gel Process …………..………………………….. 12 2.2.1 Definition of Some Terms……………….…….…………………….. 12 2.2.2 The Sol-Gel Process………………………....………………………. 13 2.3 Chemistry of Sol-Gel process……………….…………….…………… 15 2.4 Steps of Sol-Gel process…………………..…..……………………….. 16 v
2.4.1 Hydrolysis and Condensation Mechanism of Metal Alkoxides……... 16 2.4.1.1 Sol-Gel Processing Parameters…………………..…………………. 18 2.4.1.1.1 H2O/Alkoxide Molar Ratio………….......………………..………. 19 2.4.1.1.2 Role of the Catalyst……………………..………..…………...….. 19 2.4.1.1.2.1 Acid Catalyst Mechanism….…………….…….……………….. 20 2.4.1.1.2.2 Base Catalyst Mechanism………………...……………………. 21 2.4.1.1.3 Effect of the Solvent………………………….….………………. 22 2.4.1.1.4 Temperature of Reaction………………...……….………….…... 23 2.4.2 Gelation……………...…………………………………….………..... 23 2.4.3 Ageing……………..………………………………………..……….... 25 2.4.3.1 Polymerization (Polycondensation)………... …………………..…. 25 2.4.3.2 Syneresis………………….…………………………..……..…….... 25 2.4.3.3 Coarsening………………….………………..………………........... 26 2.4.3.4 Segregation………………….…………..…………………….......... 27 2.4.4 Drying………………….………………………….…………….......... 27 2.4.5 Densification………………….…………….………………….…..… 29 2.5 Advantages of the Sol-Gel process…………………………………….. 30 2.6 Limitations of the Sol-Gel Process………………..…………………… 31 2.7 Applications of the Sol-Gel Process…………………………………… 32 2.8 Sol-Gel Processed Laser……………………………………………….. 32 2.8.1 TiO2 Laser Host ………………….……………………………..…… 33 2.8.1.1 Structure of TiO2………………….…………………….………..… 33 2.8.1.2 Properties of TiO2 ………………….…………….………..……… 34 2.8.1.3 Applications of TiO2………………….………….……………..… 35 2.8.2 Dopant Ions………………….…………………………..…….……. 36 2.8.2.1 Rare Earth Ions………………….………………………….…..….. 36 vi
2.8.2.2 The Trivalent Holmium Ions (Ho3+ Ions) ………………………….. 37 2.8.2.2.1 Visible Emission of Ho3+ Ions……………….………………........ 39 2.8.2.2.2 Near-Infrared Emission of Ho3+ Ions……………….……...…..…. 40 2.8.2.2.3 Up Conversion Emission of Ho3+ Ions……………………………. 42 2.8.2.2.4 Resonance Fluorescence Process of Ho3+ Ions……………….…... 42
Chapter 3: Experimental Setup and Sample Preparation 3.1 Introduction………………...………………...........…………………… 43 3.2 The Chemical Materials………………..……….....……………..…….. 45 3.2.1 Sol-Gel Precursor ………………..……………….……….………...…45 3.2.2 Solvent ………………...………………...............……………..…….. 45 3.2.3 Other Chemical Material………………...........…….………...……… 45 3.2.3.1 Deionized Water………………....………...……….………..…..…. 45 3.2.3.2 Hydrochloric Acid ………………...……...……………..…...…….. 45 3.2.4 Active Rare Earth Ions………………..............……………….……... 45 3.3 The Glassware Apparatus……………….....…………...……………… 47 3.4 Other Used Instruments ……………….....……………..…...………… 48 3.5 Preparation System………………...............………..…..….………… 48 3.5.1 The Heater/Chiller unit………………………………………….…… 48 3.5.2 The Reactor Setup……………………………………………….….. 49 3.5.3 The Hood ………………………………………………………….... 49 3.6 Raw Materials Volume Calculation…………..……………………..… 50 3.7 Sample Preparation…………..…………….………………………....... 51 3.7.1 Preparation of Pure TiO2 Sol………………....…………………..….. 51 3.7.2 Preparation of Ho3+ Doped TiO2 Sol………………………..……….. 53 vii
3.8 Heating of the TiO2 Sol……………………….…………...………...… 55 3.9 High Temperature Treatment of the Wet Gel……………...………….. 55 3.10 Structural Characterization Calculation of the Prepared Sol-Gel Samples………………………………………………...…… 55
Chapter 4: Results and Discussion 4.1 Introduction ………………………………………………………….…. 57 4.2 Appearance of the Prepared Alkoxide Solution and Samples………..... 57 4.3 Characterization of Samples………………………………………....… 59 4.3.1 Structural Characterization of Pure and Ho3+ Doped Titania Samples………………………………………………………….…… 59 4.3.1.1 X-Ray Diffraction Analysis (XRD) …………………………….….. 59 4.3.1.2 Fourier Transform Infrared Spectroscopy (FTIR) Analysis……….. 65 4.3.2 Optical and Spectroscopic Characterization of Pure and Ho3+ Doped Titania Samples………………………….………………...… 70 4.3.2.1 Absorption Spectra…………………………………...…………….. 70 4.3.2.2 Fluorescence Emission Spectra………………………...…………. 72
Chapter 5: Conclusions and Future work 5.1 Conclusions…………………………………………………………… 78 5.2 Future Work …………………………………………………………… 80
References ………………………………………………….………..…... 82
viii
LIST OF TABLE Table No.
Table Tittle
Page No.
2-1
Electronic Configuration of Rare Earth elements and their Trivalent Ions.... 36
2-2
General Properties of Holmium Atom…………….…………..……………. 37
3-1
Analyzing Instruments for Characterizing the Synthetic Samples …....…... 44
3-2
General Properties of Used Chemical Raw Materials…………………….. 46
3-3
General Properties of Ho3+ Ions……………………………………………. 47
4-1
Grain Size and Lattice Constants of Pure and Doped TiO2 Nanopowder with Different Concentration of Ho3+ Ions…………....…….. 65
4-2
Infrared Bands Position of Pure and Ho3+ doped Titania Nanopowder with Different Concentration of the Ho3+ Dopant Ions..……………..…… 69
ix
LIST OF FIGURE Figure No.
Figure Tittle
Page No.
2-1
Chemical Structure of Titanium Tetra Isopropoxide………….…..……….. 15
2-2
An Overview of Sol-Gel Process …………………….…….……....…...… 16
2-3
Gel Structure of Acid Catalyzed Reaction (Linearly Cross Linked) …..….. 20
2-4
Gel Structure of Base Catalyzed Reaction (Branched Clusters)……...….... 22
2-5
Sol-to-Gel Conversion at the Gel Point …………………………….…….. 24
2-6
Volume Change of the Gel during Syneresis…………………….…….…. 26
2-7
Growth of Neck between Particles (Shaded Region) Due to Dissolution and Reprecipitation…………………….………..……….…… 26
2-8
Increasingthe Strength and Stiffness of the Gel ……………….……..….… 27
2-9
Obtaining a Dense Solid Product After Densification …………....……....... 29
2-10
Entrapment of Dopant (Guest) into a Sol-Gel Network (Host)……….…… 33
2-11
Unit Cells of Three Different Phases of TiO2 Nanocrystal………….….... 34
2-12
Partial Energy Levels Diagram of Ho3+ Ion……………………….…...….. 38
2-13
Schemes of Energy Level of Ho3+ Ion……………………...……….....…... 40
2-14
Absorption Spectra of Ho3+ Doped LaF3 and LaVO4 Nanoparticles.......... 41
2-15
Near Infrared Emission Spectra of Ho3+ Doped LaF3 and LaVO4 Nanoparticles …..….…………………….………………………….……. 41
3-1
Flowchart of the Practical Steps Followed in This Study ………..........… 44
3-2
Samples Preparation System…………………………………......……..... 49
3-3
The Reactor Setup…………………………..……………………..…….. 50
3-4
Scheme of Pure TiO2 Sample Preparation by Sol-Gel Method………….…. 52 x
3-5
Scheme of Ho3+ Doped TiO2 Sample Preparation by Sol-Gel Method…….… 54
4-1
Photograph of Pure TiO2 Rod……………………………….……..……….… 58
4-2
Photograph of the 7 wt% Ho3+ Doped TiO2 Rod……………………..……… 58
4-3
Photograph of the Pure and Doped TiO2 Nanopowdered Samples…….…..… 59
4-4
XRD Patterns of Pure TiO2 Nanopowder Calcined at (500C)……………… 60
4-5
XRD Patterns of 1 wt% Ho3+:TiO2 Nanopowder Calcined at (500C)………. 60
4-6
XRD Patterns of 3 wt% Ho3+:TiO2 Nanopowder Calcined at (500C)…….... 61
4-7
XRD Patterns of 5 wt% Ho3+:TiO2 Nanopowder Calcined at (500C)…..…... 61
4-8
XRD Patterns of 7 wt% Ho3+:TiO2 Nanopowder Calcined at (500C)……… 61
4-9
Lattice Constant of TiO2 Nanopowder Calcined at (500C) as a Function of Ho3+ Concentrations………………….....………….……….. 63
4-10
Grain Size of Doped TiO2 Nanopowder Calcined at (500C) as a Function of Ho3+ Concentrations……………………..…………………. 64
4-11
FTIR Transmission Spectra of Pure and Ho3+ Doped TiO2 Nanaopowder.… 66
4-12
Absorption Spectra of Pure TiO2 Gel………………………………………... 71
4-13
Absorption Spectra of Different Concentration of Ho3+ Doped TiO2 Gel…... 71
4-14
Fluorescence Emission Spectra of 3wt% Ho3+ Doped TiO2 Gel Under 450 nm Excitation at Room Temperature………...…………………... 73
4-15
Fluorescence Emission Spectra of 5wt% Ho3+ Doped TiO2 Gel Under 450 nm Excitation at Room Temperature………...………………..….. 73
4-16
Fluorescence Emission Spectra of 7wt% Ho3+ Doped TiO2 Gel Under 450 nm Excitation at Room Temperature………...……………….….. 74 xi
4-17
Fluorescence Emission Spectra of 1 wt% Ho3+ Doped TiO2 Gel Under 644 nm Excitation at Room Temperature ……...……………………. 76
4-18
Fluorescence Emission Spectra of 3 wt% Ho3+ Doped TiO2 Gel Under 644 nm Excitation at Room Temperature ………………..……….… 76
4-19
Fluorescence Emission Spectra of 5 wt% Ho3+ Doped TiO2 Gel Under 644 nm Excitation at Room Temperature ……………….…...……… 77
4-20
Fluorescence Emission Spectra of 7 wt% Ho3+ Doped TiO2 Gel Under 644 nm Excitation at Room Temperature …..……………...……… 77
xii
LIST OF SYMBOLS Symbols a a.u. B
c CaF2 CeO2
Meaning Lattice Constant of the Anatase TiO2 Phase (Å) Arbitrary Unit Full Width at Half Maximum (FWHM) Lattice Constant of the Anatase TiO2 Phase (Å) Cadmium Di-fluoride Cerium Di-Oxide
CnH2n+1
General Formula of Alkyl Group
C2H5OH
Molecular Formula of Ethanol
C12H28O4Ti
d
Molecular Formula of Titanium Tetraisopropoxide Plane Spacing in a Crystal (Å)
Dy3+
Dysprosium Trivalent Ion
Er3+
Erbium Trivalent Ion
EtOH
Ethanol
Eu3+
Europium Trivalent Ion
Fe3+
Iron Trivalent Ion
Gd3+
Gadolinium Trivalent Ion
h (hkl)
Hydrolysis Ratio; Water/Alkoxide Molar Ratio
H3 O+
Hydronium Ion
HCl
Hydrochloric Acid
HNO3 Ho Ho3+ HoCl3.xH2O H2SO4 LaF3 LaVO4 La2O3 Li+ LiYF4 M
Miller Indices
Nitric Acid Holmium Atom Holmium Trivalent Ion Holmium (III) Chloride Hydrate Sulfuric Acid Lanthanum Tri-Fluoride Lanthanum Vanadium Tetra-Oxide Lanthanum Tri-Oxide Lithium Ion Lithium Yttrium Tetra-Fluoride Metal Atom xiii
mol%
Mole Percentages
M-O-M
Metal-Oxygen-Metal Bridge
M(OEt)z
Metal Ethoxide
M-OH
Metal Hydroxide
M (OR)z
Metal Alkoxide
Mw
Molecular Weight of Chemicals (g/ml)
n
Number of Mole of Chemicals(mol)
N
Coordination Number
NaOH
Sodium Hydroxide
Nd3+
Neodymium Trivalent Ion
NH3
Ammonium
NH4OH OHOR pH Pr3+ R R-OH Si(OR)4
Ammonium Hydroxide Hydroxyl Group Alkoxide Group Specification of Acidity or Alkalinityof an Aqueous Solution Praseodymium Trivalent Ion Alkyle Group Alcohol Leaving Group Silicon Alkoxide
Sm3+ t Tb3+
Samarium Trivalent Ion Grain Size (nm) Terbium Trivalent Ion
Ti4+
Titanium Tetravalent Ion
TiCl4
Titanium Tetra Chloride
TiO2
Titanium Dioxide
TiO2-A
Titanium Dioxide with Acid Catalyst
TiO2-B
Titanium Dioxide with Base Catalyst
TiO2-N
Titanium Dioxide without Catalyst (Normal)
Tm3+
Thulium Trivalent Ion
Ti-O-Ho
Titanium-Oxygen-Holmium Bond
Ti(OR)4
Titanium Alkoxide
Ti(OPri)4
Titanium Tetra Isopropoxide xiv
V wt% W Xe Y3+ YAlO3 Yb3+ Y2 O3
Volume of Chemicals (ml) Weight Percentage Weight of Chemicals (g) Xenon Atom Yttrium Trivalent Ion Yttrium Aluminum Tri-Oxide Ytterbium Trivalent Ion Yttrium Tri-Oxide
z
Valence of the Metal Atom
Z
Atomic Number of Element
B
Bragg Angle (Degree)
Wavelength
Density of the Chemicals (g/cm3)
xv
LIST OF ABBREVIATIONS Abbreviations
Meaning
AFM
Atomic Force Microscopy
dmf
Dimethylformami
dmso
Dimethylsulfoxide
DCCA
Drying Chemical Control Addivtives
ESA
Excited State Absorption
FTIR
Fourier Transform Infrared Spectroscopy
HRTEM ICCD IR MID IR
High Resolution Transmission Electron Microscopy International Center for Diffraction Data Infrared Range of Electromagnetic Spectrum Mid Infrared Range of Electromagnetic Spectrum
NIR
Near Infrared Range Electromagnetic Spectrum
REE
Rare Earth Element
SEM
Scanning Electron Microscopy
TTB
Titanium Tetra Butoxide
TIP
Titanium Isopropoxide
TTIP
Titanium Tetra Isopropoxide
UV
Ultraviolet Range of Electromagnetic Spectrum
Vis
Visible Range of Electromagnetic Spectrum
XRD
X-Ray Diffraction
YAG
Yttrium-Aluminium-Garnet
xvi
THESIS ORGANIZATION This thesis is organized as the following: Chapter One Includes general introduction of sol-gel process for nano material preparation, and literature survey related to the preparation of pure and rare earth doped TiO2. Chapter Two Presents theoretical backgrounds about sol-gel method, as well as advantage, limitations, and some application of sol-gel method, also some general properties of TiO2 host and different emissions ability of Ho3+ ions has been explained. Chapter Three Explains experimental study via giving some information about used chemical raw materials, preparation system, also steps of pure and Ho3+ doped TiO2 samples has been clarified. Chapter Four It is the core of the thesis that presents the structural, optical and spectroscopic results of the prepared samples, and discussing them in detail. Chapter Five Contains conclusions and future works.
xvii
Chapter One
Introduction
Chapter One Introduction and Literature Survey
1.1 Introduction Nanocrystalline semiconductors are assumed as cornerstones of nanotechnology. They have a great impact on revolutionizing materials production. Also they possess a significant and pioneer role in industrial and commercial fields which give them the ability to occupy a broad area of research activity in the past decade [1, 2]. Among methods for nanomaterials preparation, the sol-gel technique is assumed as one of the most important selected methods with novel processing strategies, well-defined structures, and different shapes [3, 4]. Simply, it can be defined as a low reaction temperature route, widely used for fabrication of nanoparticles; starting from molecular precursors, an oxide network is obtained via polymerization reaction [5]. The transition from a liquid (solution) into a semi-solid (gel) explains the name of the ''sol-gel process'' [4]. Since the sol-gel chemical reactions occur in solutions, therefore; this method is also named as ''Wet Chemistry'' method [5]. Generally in this method, transition metal alkoxides are used as main reactants, which they have high purity and more reactivity towards water, so they need great care to obtain gels [6]. There are numerous parameters which have an important influence on structural properties of the final products via sol-gel technique, such as: nature of precursors, molar ratios between reactants, amount of used water, type of the catalyst, and reaction temperature [4].
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Chapter One
Introduction
In fact the sol-gel method offers the opportunity to synthesis the optical materials [7], via formation of the transparent host and allowing addition of high dopant concentration to the host. One of the good candidate material for this field that attracted more attention is titanium dioxide (TiO2) which belongs to the family of metal oxides, because it has high transparency in the visible wavelength region, and high refractive index, therefore it has been considered to be a potential host for lanthanide gusts [8, 9 ]. Among chemical elements in the periodic table, groups of rare earth elements or (lanthanide series) are recorded as the most fascinating group of elements; these groups are located at the bottom of the periodic table, one row above actinides [10]. Inside the family of lanthanide ions, triply ionized holmium ion (Ho3+) is the active member, and has a great importance due to its ability to emit various wavelengths, especially in both visible and near infrared (NIR) region of the electromagnetic spectrum, so this make holmium ion doped solid materials behave as an optical material [11]. On the other hand, Ho ions can emit in the mid infrared (MID IR) region of the electromagnetic spectrum range which can be used in the field of surgery and medical applications [12]. Also it can enhance the photocatalytic activity of TiO2 for destruction of organic pollutants in gas or liquid [13, 14]. Due to these important applications of Ho ions, it has being mostly studied among all the other rare earth ions.
(2)
Chapter One
Introduction
1.2 Thesis Objectives The thesis aims to prepare and analyze lasing material through the followings: Accommodating rare-earth active ions (Ho3+ ions) in a (TiO2) host by sol-gel technique for the preparation of laser active medium. Investigating the structure of the synthetic samples. Characterizing the optical and spectroscopic behavior of the prepared doped samples as a function of the dopant concentration ( Ho3+ ions).
1.3 Literature Survey 1.3.1 Pure TiO2 Preparation In (1986) Yoldas [15] studied the hydrolysis of titanium alkoxide, he obtained that titanium alkoxide hydrolyse vigorously with water producing polycondensates whose equivalent oxide content varies from ~ 70% to over 90%. He also studied the effect of catalyst on the morphologies of oxide materials derived from polycondensates. The honeycomb morphology of the final product formed under basic condition while the particulate granular morphology of the products formed under acid condition. The experimental results showed that it is also possible to form clear polymer solutions under excess water hydrolysis with addition of certain acids, and gelling time of the solutions was a function of solution concentration and water/alkoxide ratio. There was a shrunk in the gel which was formed from the clear solutions and the oxide content of the gel increased as they shrunk.
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Chapter One
Introduction
Harris and Byers (1988) [16] studied the effect of the solvent system in the preparation process of colloidal titania by hydrolysis of titanium ethoxide in ethanol, 1-butanol, and tert-butyl alcohol. Electron microscopy showed that spherical titania particles were formed in ethanol and 1-butanol solvents, while agglomerated and irregular shape formed in tert-butyl alcohol. Wang and Ying (1999) [17] studied the sol-gel synthesis of nanostructured TiO2 to examine the processing parameters that control crystallite size and phase. The samples were synthesized with high water:alkoxide ratio, and subjected to hydrothermal treatment at 80-240 °C for 1 day. The titania gel was successfully crystallized to the anatase phase at relatively low temperatures through hydrothermal aging. Nanocrystalline anatase materials with grain sizes of 6, 10, and 28 nm were obtained from hydrothermal treatment at 80, 180, and 240 °C respectively. Titania powders were synthesized via sol-gel method using titanium tetrabutoxide (TTB) as a main precursor by Farias (2002) [18]. The synthesis was performed in water and in solutions of dimethylformamide (dmf), dimethylsulfoxide (dmso). X-Ray Diffraction (XRD) pattern showed that, the samples obtained in (dmf) or (dmso) solutions were crystalline (anatase phase) with some minor amount of brookite phase, while the samples synthesized in water was amorphous. Nanosized TiO2 powders were obtained from titanium tetrachloride (TiCl4) precursor under various pH values by Hu et al. (2003) [19]. The prepared titania existed in the form of nanocrystalline anatase with some brookite, which was evidenced by (XRD) analysis. The average crystallite sizes of the TiO2 particles heat treated at 450 oC for 2 h were in the range of (7- 9) nm.
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Chapter One
Introduction
Santana-Aranda and co-workers (2005) [20] synthesized TiO2 nanopowders by sol-gel method. Different gelling pH were set to the values of 3 (A-acid), 7 (N-normal) and 9 (B-base) by addition of ammonium hydroxide (NH4OH) or hydrochloric acid (HCl) to observe its effect on the properties of the material. Transmission Electron Microscopy (TEM) results showed that (TiO2-A) samples had the smaller particle size and had granule shape, while (TiO2-N) and (TiO2-B) particles were agglomerates of small particles slightly bigger than (TiO2-A) particles. In (2007) Pal et al. [21] prepared nanometer-size spherical titania particles by controlling hydrolysis of glycolated precursors, they studied the effect of annealing on the morphology, size shrinkage, and phase transformation of the nanoparticles by (XRD) pattern, Scanning Electron Microscopy (SEM), Raman spectroscopy, and High Resolution Transmission Electron Microscopy (HRTEM). Results showed that the higher water content and very high concentration of titanium glycolate in acetone produced titania particles of heterogeneous size. The crystallinity of the particles could be improved by annealing at high temperature, which leads the titania nanoparticles to undergo amorphose-anatase-rutile phase transformation. El Mir and co-workers (2008) [22] prepared transparent TiO2 monoliths. The preparation method was based on a sol–gel technique using i
titanium tetraisopropoxide [Ti(OPr )4] as a precursor. By controlling the hydrolysis of the precursor, and rate of drying, transparent TiO2 xerogel monoliths were obtained at room temperature which had an amorphous structure and transparent to wavelength range (400-1400) nm. After heat treatment at 550 oC for 6h, this amorphous phase was transformed into anatase phase.
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Chapter One
Introduction
Pure TiO2 gels at the molar ratio (1: 1: 10: 0.1) of (TTIP: H2O: EtOH: HCl) components prepared by Adnan et.al (2009) [23] using sol-gel method. The structural characterization of the pure TiO2 samples was carried out by (XRD) analysis; its result showed that all of the prepared samples had amorphous structure. After calcinations at 500°C for 1h, the typical peaks of crystalline anatase nanoparticles have been observed. By using Scherer's formula the grain size of the prepared anatase phase was calculated which was equal to 15 nm. TiO2 nanoparticles were prepared via hydrolysis of titanium tetra isopropoxide (TTIP) by Lim et al. (2010) [24]. The influence of pH on the reaction morphology was evaluated depending on the type of the used catalysts such as: acid (HCl) and base (NH4OH). In the case of using base catalyst, the morphology of the TiO2 particles exhibited a powder form, while in the case of using acid catalyst it had a bulk or granular form. Sol-gel method had been used by ˘Cenovar and co-workers (2012) [25], for preparing nanosized TiO2 from (TTIP). The effect of heat treatment at different temperatures on the phase of prepared TiO2 samples were carried out and analyzed by XRD technique. XRD pattern of the sample calcined at 250 o
C showed amorphous structure and transformation to anatase phase were
calcined at 380 oC. While for the sample which heat treated at 550 oC pure anatase phase was obtained. Pattern of the sample treated at 650 oC indicated presence of anatase and rutile phases which transform into pure rutile phase at 800 oC. Results showed that increasing the calcination temperature influenced increasing the size of the crystalline particles from 6nm at 250 oC, to more than 100 nm at 800 oC.
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Chapter One
Introduction
Shahab et. al. (2013) [26] prepared pure TiO2 nanoparticles using TiCl4 precursor. The starting solution was prepared at room temperature, after increasing the viscosity of the prepared sol, it was changed in to gel, after some thermal treatments; the obtained gel changed to a white anatase powder. The composition of TiO2 prepared powder was characterized by Fourier Transform infrared spectroscopy (FTIR), which indicated O-Ti-O bond formation. UV spectra of the prepared sample showed that the peak of TiO2 nanoparticles formed below 325 nm. Agarwala and co-workers (2014) [27] studied the effect of boiling point of solvent on the growth of TiO2 nanoparticles that affected on the particle size. They prepared two types of TiO2 nanoparticles by non-hydrolytic sol-gel method. Ethanol and benzyl alcohol were used as organic solvents. The particles that synthesized with ethanol were heat treated for 1h at 500oC while for 5h at 450oC when synthesized with benzyl alcohol. The average size of the particles which prepared with ethanol was 20-30 nm and for particles synthesized with benzyl alcohol was 40-60 nm.
1.3.2 Rare Earth Doped TiO2 Preparation The photocatalytic activities of the mixtures of TiO2 (P25) with three rare earth oxides were investigated by Lin and Yu (1998) [28]. The effects of the rare earth oxide contents and calcinations temperature on the photocatalytic activities were studied. They obtained that the mixtures of TiO2, with La2O3 (0.5 wt%) or Y2O3 (0.5 wt%) calcined at 650°C or 700 °C exhibit higher photoactivity than pure TiO2 for the oxidation of acetone in air, while the mixtures of TiO2 with CeO2 had lower photoactivity. (XRD) pattern showed that the presence of rare earth oxides inhibited anatase to rutile transformation at elevated temperature. The activity differences were due to
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Chapter One
Introduction
the change in the amount of surface hydroxyl groups resulting from the interaction between the rare earth oxides and TiO2. In (2002) Capobianco et.al [29] prepared Ho3+ doped nanocrystaline Y2O3 as a function of holmium concentration (0.1, 0.5, 1, 2, 5, and 10 mol %). The prepared samples emitted various wavelengths in the visible region, Such as blue in the range (480-500) nm, yellow in the range (530-580) nm, Red in the range (630-680) nm, while NIR emission was observed in the range (735-775) nm, all these emissions were obtained under 457.9 nm excitation. Burns and co-workers (2004) [30] used sol-gel method to prepare undoped and doped titania, they studied the effect of neodymium ions (Nd3+) on both titania lattice and anatase to rutile phase transformation. The anatase lattice was shown to deform predominantly along with the c-axis to accommodate substitutionally-incorporated Nd3+ ions. The maximum in elongation of the c-axis occurred at Nd3+ concentration of 0.1 mol%. This suggested some incorporation of Nd3+ ions on the interstitial sites. On the other hand, anatase-to-rutile phase transformation was retarded due to the presence of dopant ions. The un-doping, single-doping and co-doping TiO2 nanoparticles were prepared by Wen Shi et.al. (2007) [31] via sol–gel method. They obtained that Fe3+ doping broadened the absorption profile, improved photocatalytic activity of TiO2. On the other hand, Ho3+-doping restrained the increase of grain size, leads to crystal expansion and matrix distortion. The photocatalytic activity of TiO2 co-doped with Fe3+ and Ho3+ ions was markedly improved due to the cooperative actions of the two dopants.
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Chapter One
Introduction
Holmium-doped lanthanum aluminate (LaAlO3) powder phosphors prepared by Singh et.al (2008) [32] using the combustion route. Emission spectra of the prepared samples showed emission in the visible range nearly at 543 nm (green), and 644 nm (red) at 453 nm excitation. Ho-doped TiO2 nanoparticles with higher photocatalytic activity prepared by Heshan et al. (2008) [13] via acid-catalyzed sol-gel method. They studied the effect of Ho doping on the crystallite sizes, and crystal pattern via (XRD) analysis. They obtained that XRD pattern of pure and doped TiO2 nanoparticles calcined at 500 oC were similar, in which TiO2 exists as a single anatase phase, whereas both anatase and rutile phase were obtained when calcined at 650oC. Also results indicated that Ho-doping could inhibit phase transformation from anatase to rutile and suppress the growth of the crystallite size. Kallel and co-workers (2009) [33] prepared TiO2 nanoparticles co-doped with Yttrium ions (Y3+) and Lithium ions (Li+) by sol-gel method. After characterizations of the prepared samples, results showed that, due to the difference between the ionic radii of Titanium ions (Ti4+) (0.64Ao) and Y3+ (0.95 Ao), Y3+ did not enter TiO2 crystal lattice to substitute Ti4+ but was adsorbed at the surface of the TiO2 particles, also Li+ was located at the surface of the sample. Luminescence measurement results showed that, Li + induced an important emission peaking at 724 nm. This luminescence emission was more intense when samples were annealed at 800 oC. In (2009) wen-Shi et.al [14] prepared Ho-doped TiO2 nanoparticles by sol-gel method. Experimental results indicated that Ho-doping could increase the surface area of TiO2 nanoparticles, caused an inhibition of the growth of crystalline size and the anatase-to-rutile phase transformation, this may be due to the formation of Ti-O-Ho bonds in the TiO2 structure.
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Chapter One
Introduction
Reszczynska and co-workers (2012) [34] used sol-gel method to prepare Erbium ions (Er3+) and Ytterbium ions (Yb3+) doped TiO2 nanoparticles. They used titanium isopropoxide as the main precursor. After the preparation of samples, they were subjected to many characterizations. Results of the optical study displayed that the absorption spectra of Yb3+ and Er3+ doped TiO2 showed stronger absorption in the (UV-Vis) region than pure TiO2. The photoluminescence spectra of both Er3+-TiO2 and Yb3+-TiO2 samples under excitation at 532 nm were observed at 670 nm for Er3+and at 580 and 640 nm for Yb3+. Pal et al. (2012) [35] prepared TiO2 nanoparticles doped with Europium ions (TiO2: Eu) with different doping concentrations via controlled hydrolysis of (TTB) under appropriate pH and temperature. The structure of the prepared samples were characterized by XRD-technique, results showed that the amorphose nanoparticles could be converted to a pure anatase phase through air annealing at 500°C for 2h. With increasing dopant concentrations, crystal size of titania particles decreased gradually. Results of the optical characterization indicated that under ultraviolet excitation, samples showed the characteristic emission corresponding to the 5D0-7Fj transition of Eu+3 ions. Synthesizing of Yb3+ doped TiO2 nanoparticles via sol-gel technique was done by Hamza and co-workers (2013) [36], to investigate the effect of Yb3+ doping on the optical properties of titania in (MID IR) range. The prepared Yb3+-TiO2 samples had polycrystalline structure in anatase phase. (FTIR) spectra showed that a single transmission peak at wave number around 1145 cm−1 was obtained for pure and doped samples after annealing process. Concentrations of Yb+3 affected on the transmission rate of this peak, and its value rose from 1.82% (for pure TiO2) to 58.1% (for doped with 1.13 wt% Yb+3).
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Chapter One
Introduction
Cao et.al. (2013) [37] prepared Samarium (Sm3+) doped anatase, and rutile monophase TiO2 nanoparticles with various doping concentration (0.5-8 mol%) under different annealing temperature (450-950) °C by using the solgel process. The optical properties of the doped samples showed that when the concentration of Sm3+ ions was 0.5 mol%, the emission intensity was low, due to the number of Sm3+ active ions were little. When Sm3+ ions concentration increased to 1 mol%, the emission intensity was increased. After increasing Sm3+ ions concentration to 2-8 mol%, emission intensity continued to weaken. Exactly for more than 2mol%, concentration quenching was observed. Result of emission spectra showed that Sm3+ doping exhibit strong orange-red emissions at (580, 613, 666, and 730 nm). Nd3+ doped titania were prepared through wet chemical synthesis method by Hamza et al. (2014) [38]. They used (TIP) as a titania precursor. XRD patterns showed that the prepared samples were amorphous. The optical properties of the samples obtained from absorption and emission spectra, they obtained that; the excitation wavelength 795 nm gave a fluorescence peak around 1069 nm, which was close to fluorescence peak of Nd:YAG crystal in NIR region. This suggests that sol-gel technique could be use for the preparation of Nd:TiO2 as the active medium of solid state laser. Keerthana and co-workers (2015) [8] prepared pure and Gadolinium (Gd3+) doped TiO2 nanocrystals by using the sol-gel method using (TIP) as the precursor for the preparation of titania sol. The prepared sol was left to stand for the formation of gel and dried at 100°C for 1h to remove solvents. The dried gel was milled into powder and calcined at 400°C for 3h. (XRD) results of the pure TiO2 confirmed that the particles crystallized purely in anatase phase. From the absorption spectrum of the doped sample, a significant shift of the absorption edge towards the visible region was observed as compared to the pure TiO2. This result indicated that doping had the effect on the optical properties of TiO2. (11)
Chapter Two
Theoretical Background
Chapter Two Theoretical Background 2.1 Introduction The sol-gel method for preparing nano materials has been obtained a pioneer role and receiving the vast opportunity to be more spectacular. In this process, mixtures of liquid solutions are reacted through chemical reactions; leading to polymerization to give the wet gel, then several heat treatments requires for obtaining final dense product [39, 40]. Since metal alkoxide is the best starting precursor (initial raw materials) for preparation of products by sol-gel method [41], therefore study of alkoxide chemistry will be focused on in this chapter, also steps of sol-gel process, these parameters which affect this process, advantages and applications of this valuable method are described. On the other hand, the ability of doping sol-gel derived materials (hosts) with controlled amounts of lasing species for use in solid state lasers are explained.
2.2 Fundamental of the Sol-Gel Process 2.2.1 Definition of Some Terms Collide: is a suspension in which the dispersed phase is so small (~ 1-100 nm) that the gravitational forces are negligible and interactions are dominated by short-range force, such as vander waals attraction and surface charges. The inertia of the dispersed phase is small enough that exhibit Brownian motion, a random wallk driven by momentum imparted by collisions with molecules of the suspending medium [42]. Sol: is a colloidal suspension of solid particles in a liquid [42, 43].
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Chapter Two
Theoretical Background
Gel: A gel is a porous interconnected solid network that expands in a stable fashion throughout a liquid medium and is only limited by the size of the container [39]. Alcogel: is the gel which is formed in an alcoholic media, and its pores are filled with alcohol [44]. Xerogel: is the result of evaporation method for drying of a wet gel, the final volume of the gel is smaller than the volume of the wet gel. Aerogel: is the result of hypercritical drying of a wet gel, there is no change in its volume compare with the volume of the wet gel [45]. Gel point: is the point at which sol (viscous liquid) transforms into gel (solid structure with elastic property) [39].
2.2.2 The Sol-Gel Process The chemical synthesis of materials which have practical importance by sol-gel method has become an area of significant importance in the field of material science. Generally, the common starting precursors for sol-gel process are metal alkoxides, they are members of the family of metalorganic compounds in which organic groups are bound to a metal via oxygen [42, 46, 47], and they are popular precursors because they react readily with water which assumed as a famous property of these alkoxides, therefore; they must be handled with an extensive care in a dry environment (in the absence of moisture) [3, 42]. They have the general formula [42, 48]: M (OR)z Where: M: is the central metal atom.
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Chapter Two
Theoretical Background
R: is the alkyle group, (R=CnH2n+1), n=1, 2, 3,… . For different value of (n), there are different alkyl groups, such as methyl (CH3), ethyl (C2H5), propyl (C3H7), butyl (C4H9), … (CnH2n+1). z: is the valence of the metal atom. Another property of these types of alkoxide precursors is high solubility in organic solvents, and they are easily transformed into chemically reactive forms of hydrated oxides on hydrolysis [42]. The more reactivity of metal alkoxides than silicon alkoxides belong to the lower electronegativity of the metal as compared to the silicon, and the ability of the metal atom to exhibit several coordination states. As a result of the latter property, coordination expansion spontaneously occurs when the metal alkoxide react with water [5, 42]. Titanium alkoxide Ti(OR)4
is a member of the family of metal
alkoxides, which has oligomeric structure than monomer [49]. The oligomerization of metal alkoxides finds its origion in the tendency of metal atom to maximize its coordination number even by bonding nearby alkoxide molecules. This may be achieved by using vacant metal orbitals to accept the oxygen lone pair from alkoxide ligands [50]. As mentioned above, metal alkoxides are generally very reactive species; this may be due to the presence of electronegative alkoxy groups making the metal atom highly prone to nucleophilic attack [49]. In this study, titanium tetraisopropoxide (TTIP) which is a member in the family of transition metal alkoxides was used as a main precursor to synthesis (TiO2) nanocrystal as a host of a solid state laser. Its chemical structure is depicted in the figure (2-1).
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Chapter Two
Theoretical Background
Fig. 2-1: Chemical structure of titanium tetra isopropoxide [51].
2.3 Chemistry of the Sol-Gel Process Unlike the traditional method in which glasses and ceramic materials are obtained at high temperature, the sol-gel route relies upon polymerization reactions in liquid solution at temperature near ambient, typically alkoxide precursor, solvent, water, and catalyst are mixed into solution [52], after a series of hydrolysis and condensation reactions; the sol particles will be formed [42]. As the polymerization reaction proceeds, the viscosity of the solution increases [52] and the sol particles undergoes transition to a ''wet gel'' via gelation [53]. The produced gel is composed of interconnected pores which initially contain alcohol, un reacted precursors, and water. Upon drying the porous gel shrinks as the fluids in the pores are evaporated. Upon further heat treatment (calsination), the porous gel converts to dense products [52]. Whole sol-gel process is demonstrated in figure (2-2).
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Chapter Two
Theoretical Background
Fig. 2-2: An overview of sol-gel process [54].
2.4 Steps of the Sol-Gel Process Formation of the sol occurs via hydrolysis, condensation reactions, in gelation step; transformation of the sol into a wet gel has been occurring. The conversion of the wet gel into dense product requires some thermal treatments. Each step has a great role on the properties of the final product. In this section, each step had been explained with more details. 2.4.1 Hydrolysis and Condensation Mechanism of Metal Alkoxides The initial step of the sol-gel process is the hydrolysis of metal alkoxides M (OR)z upon adding water or water/alcohol solution and the result is the generation of the metal hydroxide (M-OH). The detail of hydrolysis process can be demonstrated in three step mechanisms as shown below [5]:
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Chapter Two
Theoretical Background
….. (2-1) The first step (a) involves a nucleophilic addition of a water molecule to the positively charged metal atom M. The second step is the transition state (b) includes transfer of proton from entering water molecule to the negatively charged oxygen of a nearby adjacent OR group, leading to the intermediate state (c). The third step (d) consists of a departure of the better leaving group ROH which should be the most positively charged species within the intermediate state (c). The whole process (a) to (d) follows a nucleophilic substitution mechanism. As soon as the hydroxo groups are generated in the solution, the condensation process takes place simultaneously and this reaction builds a metal-oxygen-metal bridge (M-O-M). Details of condensation reaction can be represents in terms of these three competitive mechanisms [5]: Alcoxolation: is a reaction by which a bridging oxo group is formed through the elimination of an alcohol molecule. The mechanism is basically the same as for hydrolysis with M replacing H in the entering group:
….. (2-2)
Oxolation: it follows the same mechanism as alcoxolation, but the R group of the leaving species is a proton, as shown below: (21)
Chapter Two
Theoretical Background
….. (2-3) Olation: when the full coordination of the metal atom is not satisfied in the alkoxide (N-Z≠0), the condensation reaction can occur by forming bridging hydroxo groups through the elimination of H2O or ROH molecule, as depicted below:
….. (2-4)
These four reactions (hydrolysis, alcoxolation, oxolation, and olation) involved in the transformation of initial
precursors into an oxide
network [5, 42]. Actually both of hydrolysis and condensation reaction may simultaneously occur, so it is impossible to describe these two processes by separate [50].
2.4.1.1 Sol-Gel Processing Parameters The characteristics of sol-gel products are related to the number of factors that have a significant role on the rate of hydrolysis and condensation reactions, by controlling these factors; it is possible to control the structure and properties of the derived inorganic network [54]. In this sub-section we will discuss the effect of each one of these factors in more details:
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Chapter Two
Theoretical Background
2.4.1.1.1 H2O/Alkoxide Molar Ratio Possibly the most important parameter which has a vast influence on the success of obtaining different structure in polymer system is hydrolysis water concentration [46], which is named as hydrolysis ratio (h) (also named as R-molar ratio), which is assumed as one of the main parameters that can be easily adjusted. It is represents by this formula [5]: h
[H 2 O] [M(OR) z ]
…..(2-5)
The water content in the solution affects critically the rate of hydrolysis relative to condensation [3]. An increase of the value of (h) promote the hydrolysis reaction by increasing the number of sites to be hydrolyzed, and since the water is the by-product of the condensation reaction, so it retards the reaction and causes more complete hydrolysis of monomers before the occurrence of condensation. In such a case the gel time increased and this would be favorable for the formation of less cross-linked product. Conversely, a reduction of (h) value increases the chance of condensation of only partially hydrolyzed molecules, and producing highly cross-linked product [55].
2.4.1.1.2 Role of the Catalyst Another important factor that affects the characteristics and properties of the sols and the produced gel is the catalyst, which adjusts the pH of the water used to perform hydrolysis. Generally, catalyst can be divided into two major categories: acid and base, both of them can influence the hydrolysis and the condensation rates and also the structure of the condensed product [42]. In this sub-section we will discuss both types in details.
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Chapter Two
Theoretical Background
2.4.1.1.2.1 Acid Catalyst Mechanism This type of catalyst serves to protonate negatively charged alkoxide group (OR), enhancing the reaction kinetics by producing better leaving groups and eliminating the requirement for proton transfer within the transition state [42].
….. (2-6) The acidic conditions favor hydrolysis, which means that fully or nearly fully hydrolyzed species are formed before condensation begins. Consequently all (OR) groups can be hydrolyzed as long as enough water is added [5]. The acid catalyst can influence both hydrolysis and condensation rates and the structure of the condensed product [6]. This is because the acid catalyst is especially suitable to promote decoupling between hydrolysis and condensation [56]. High acid concentration severely retard the condensation kinetics, so the more extended and less branched polymer (low cross-link) can be obtained during the use of such kind of catalyst [42]. As depicted in the figure (2-3).
Fig. 2-3: Gel structure of acid catalyzed reaction (linearly cross linked) [57].
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Chapter Two
Theoretical Background
Generally, inorganic acids such as HCl, HNO3, and H2SO4 are used as acid catalysts. Among these, HCl is the most commonly used. This may be due to the lower electronegativity of the chloride anion compared to the others, and bonding of the chloride ion to the Ti atom as a monodentate ligand, while sulfate and nitrate ions can be bonded as bidentate ligands causing a strong interaction between the Ti atom with sulfate and nitrate anions. For this reason, the chloride anion can be removed easily from the metal atom when the hydroxyl ion is attracted to the metal atom. On the other hand, Organic acids cannot be favored as catalyst, since they react easily with metal alkoxides and these are generally bounded to the metal atom as bidentate ligands. In these reactions alkoxide group are easily replaced by carboxylate groups [5, 6, 15].
2.4.1.1.2.2 Base Catalyst Mechanism During the use of the base catalyst, the nucleophilic power of the entering molecules increases, so it is likely that water dissociate to produce nucleophilic hydroxyle anions (OH-) in a rapid first step [58], which displace (OR) groups from the metal alkoxide (M-OR), and forming (M-OH); then the condensation is always activated through the formation of strong nucleophiles (M-O-) by deprotonation of hydroxo species (M-OH) [5, 42]. M OH : B M O BH
….. (2-7)
Where: B=NaOH, NH3, or any other base. Generally, base condition favor condensation reaction, therefore; the condensation begins before hydrolysis is complete and this leads to highly branched polymer (strongly cross linked) as shown in figure (2-4).
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Chapter Two
Theoretical Background
Fig. 2-4: Gel structure of base catalyzed reaction (branched clusters) [57].
2.4.1.1.3 Effect of Solvent It is known that high reactivity of transition metal alkoxides with water is one of the main disadvantages of them. They need handling in a dry atmosphere, otherwise; precipitation is usually observed rather than gelation [5, 42]. Alkoxide reactivity can be easily modified by using the chemical additives to retard the hydrolysis and condensation reaction rates in order to control the condensation pathway of the evolving polymer. Such additives can be solvents, the most often used solvent is alcohol [48, 49]. The solvent also used to prevent liquid-liquid phase separation during the initial stages of the hydrolysis reaction (i.e. prevent the immiscibility). As mentioned above, metal alkoxides are often dissolved in the organic solvent (alcohol) before performing hydrolysis reaction; two different kinds of solvent may be distinguished [50]: Alkoxide dissolved in their parent alcohols, which have the same number of carbon atoms in the alkyl group as in the alkoxy group of the metal alkoxide, for example: ethanol (EtOH) is the most suitable solvent for a metal ethoxide M(OEt)z. Alkoxide dissolved in alcohol with different organic groups.
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Chapter Two
Theoretical Background
In both cases the alcohols are often not chemically inert toward metal alkoxides and may interact with them changing its original properties.
2.4.1.1.4 Temperature of Reaction Generally, the temperature of the reaction has a great influence on the rate of both hydrolysis and condensation reactions; by increasing the temperature both of these two reactions are activated. At high temperature the rate of collision of sol particles increases, higher particles collision rates imply higher rates of bond formations through polycondensation. This shows the direct affect of temperature on the gel formations. Also, high reaction temperature causes shorter gelling time of sol particles and reduces shrinkage of the wet gel during the drying step, and obtaining a densely dry gel [53]. For poorly reactive precursors such as Si(OR)4, the temperature may be increased to activate the sol-gel transition. While for strongly reactive precursors such as transition metal alkoxides, as an example; Ti(OR)4, the temperature must be lowered in order to slow down hydrolysis and condensation process [5].
2.4.2 Gelation After hydrolysis and condensation reactions which lead to formation and growth of the sol particles, gelation is the third steps of the sol-gel process [42]. Gelation is a spectacular event in which the solution suddenly loses its fluidity and takes on the appearance of an elastic solid [59]. This means that a sol can be transformed into gel by going through a point which is called a gel-point. Exactly, It occurs when links are formed between sol particles to form cluster (the sol abruptly changes from a viscous liquid state to a solid phase called the gel) [39], as depicted in figure (2-5).
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Chapter Two
Theoretical Background
Precursor
Sol
Gel
Fig. 2-5: Sol-to-gel conversion at the gel point [39]. (a) Mixing of precursors, ( b) sol formation, (c) gel formation.
At this point, although the mixture has a high viscosity but low elasticity [57]. Continuing of gelation, further cross-linking of the sol particles leading to the increase in the elasticity of the obtained gel, and the final structure of a gel consists of two components system of a semisolid nature rich in liquid [42]. The gelation time is defined as the standing time for which no more fluidity was observed during tilting the solution container. Gelation time depends on the reactivity of the alkoxides; silicon alkoxides are not very reactive in the reactions, its gelation occurs within several days after water have been added; on the other hand, titanium alkoxides are very sensitive to humidity, and they have gel times in seconds or minutes, for this reason they must be handled in a dry atmosphere so as to avoid precipitation.
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Chapter Two
Theoretical Background
2.4.3 Ageing The chemical reactions that cause gelatin do not stop at the gel point, therefore elastic property of the gel will continue to change long time after the gel point [42] which lead to the change in the structure and property of the gel beyond gelation [43] this process is known as ageing and it is commonly a slow process [60]. The strength of the wet gel increases with ageing, which reduces the chance of cracking in the drying step [54]. During ageing step many changes happen in the solid phase of the gel, such as modification in its whole size [59, 60]. Generally these changes can be categories as:
2.4.3.1 Polymerization (Polycondensation) Due to increasing the number of bridging bonds in the reactions, equations ((2-2)-(2-4)), the connectivity of the gel network increases, this lead to increase the elasticity of structure of the gel long after gelation [42].
2.4.3.2 Syneresis The shrinkage of the porous gel body with expulsion of liquid from its pores without any evaporation of the solvent is called syneresis. As the condensation reaction proceed, the increase in bridging bonds causes contraction of the gel network, as it is shown in figure (2-6). The rate of syneresis decreases with time, this could results from increasing the stiffness of the network as more bridging bonds are formed and the solid structure become more tightly packed [59].
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Chapter Two
Theoretical Background
Fig. 2-6: Volume change of the gel during syneresis [39].
2.4.3.3 Coarsening Coarsening is also called ripening; is a process of dissolution and reprecipitation driven by differences in solubility. In this process, when a gel is immersed in a liquid in which it is soluble, material dissolves from the surface of large particles (convex surfaces), and deposits on the initially narrow "necks" (concave surfaces), this joins particles to each other. Then, these necks will grow; and small pores are filled in, resulting in the increase in the average pore size of the gel [59]. The above mentioned process are shown in both figures (2-7) and (2-8).
Fig. 2-7: Growth of neck between particles (shaded region) due to dissolution and reprecipitation [42].
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Chapter Two
Theoretical Background
Fig. 2-8: Increasing the strength and stiffness of the gel [42].
2.4.3.4 Segregation In some cases, ageing leads to the development of inhomogeneity. Where gelation has occurred very quickly (e.g. in base catalyzed conditions) or where several precursors of different miscibility with water have been used, there is a possibility that the porous gel contains isolated regions of un-reacted precursor [59].
2.4.4 Drying After sol formation and converting it into a wet gel via gelation, alcohol and water are no longer needed; so the prepared gel must be dried in order to remove the water and solvents which they are formed as by-products of condensation reactions [3, 53]. There are two possibilities to dry the wet gel. The first one is drying by evaporation which results in the production of xerogel [45]. Before drying of the wet gel, all of its pores are filled with solvent and the liquid/vapor interfaces are not present. As drying proceeds, the gel network becomes more restricted, and the removal of liquid leads to the formation of such interface and development of capillary stress which causes cracking in this type of gel. (11)
Chapter Two
Theoretical Background
On the other hand, gels can be dried more easily at supercritical conditions in an autoclave this method is named as supercritical drying or hypercritical drying [39, 61]. This type of drying is assumed as the second possibility of drying that results in the production of aerogel [45], which it is an effective method that can be used to reduce cracking, because it can eliminates the liquid/vapor interface by heating the gel to a point above the critical temperature of the solvent [59]. The external size of the hypercritically dried gel (aerogel) almost equal to those of the original wet gel, almost no shrinkage occurs [61], this is because no compressive stress is applied to the solid phase during drying [59]. The method of drying is influenced by the intended use of the dried material; if powder is desired, no special care is needed to prevent fragmentation, while; if monolith is desired, special care must be taken to ensure complete removal of organic groups during drying. During the initial stages of drying, the volume change of the gel is equal to the volume of the evaporated liquid [3]. The familiar tendency of gels to crack during drying results from the high capillary stresses in a small pore, and the resistance to fluid flow in these small pores could fracture the wall separating it from neighboring pores [59]. To favor obtaining of monolithic pieces of dried gel, some drying control chemical additives (DCCA) have been used, which can really acts as a structure modifier [62]. These additives can decrease the capillary forces during the drying step of the sol-gel process [63], and the result is the reduction of micro-fracturing and decreasing the risk of cracking of the gel network.
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Chapter Two
Theoretical Background
2.4.5 Densification After drying, the last step of preparation of product by the sol-gel process is densification (also refers as calcination or sintering) in which the high temperature is required for the elimination of the pores of the dried gel, finally a pore free dens material will be obtained [43, 44], as it shown in figure (2-9). Typically, the structure of the gel which is obtained after drying is amorphous, but calcinations induce crystallization [60, 64].
Fig. 2-9: Obtaining a dense solid product after densification [65]. (A) sol, (B) wet gel, (C) dried gel, (D) final dense product.
Almost all the problems that arise during the densification step are closely related to the pore size of the gel; gels contain only small pores tend to fracture when heated to a high temperature, while these gels have a large pores can be sintered without such problem. In order to obtain fracture-free monolithic product from gels of relatively small pore it is necessary to take special care in the temperature ranges this means that heating of the gel at very slow rate to avoid fracture [53].
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Chapter Two
Theoretical Background
2.5 Advantages of the Sol-Gel process The sol-gel process has many notable advantages that make it a good candidate method for synthetic of material, some of these advantages are: High degree of homogeneity is readily attained on a molecular scale during mixing of liquid precursors [43, 44, 66]. Better purity of the final products due to purity of the initial raw materials [40]. Higher uniformity of doping ions distribution exists and higher doping concentration becomes possible. Highly dense products can be obtained at higher annealing temperatures [43]. Optically transparent products can be obtained via this novel method, [54]. Obtaining chemical composition of crystalline and non crystalline products, such as TiO2 and SiO2 respectively [40]. Glasses can be prepared at lower temperature comparing with the traditional method which requires high temperature [44]. Not only massive pieces, it can be casted as monoliths, coated as thin films on slides, and crush into powder [44, 54].
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Chapter Two
Theoretical Background
2.6 Limitations of the Sol-Gel Process Besides the above advantages, there are limitations that limit the activity of sol-gel process during material preparation, such as: This process is time consuming (long processing time). The raw materials which are used during the sample preparation by this method are often expensive [40, 42, 57]. Difficulties arise during working with metal alkoxides because they are very reactive toward water in the hydrolysis step, and the rate of their reactions are too fast, most of the time precipitates will be formed rather than clear sol and this leads to the loss of morphological and also structural control over the final oxide material [46]. During drying step, shrinkage of the wet gel is observed [40, 42, 57]. During densification step, it is difficult to completely remove the residual hydroxyls from the sol-gel product. To get rid of these organic groups sample has to be annealed above 1000 oC, and this may produce undesirable side effects [43]. Difficulties in the synthesis of monoliths due to cracking [4]. The sol-gel synthesis of ceramics will never be able to compete for the mass production of some large scale materials such as window glass for which the conventional processes can rely on much cheaper raw materials [39]. Health hazards of organic solutions which used for preparation of samples [40].
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Chapter Two
Theoretical Background
2.7 Applications of the Sol-Gel Process Despite the above limitations, the sol-gel method has a good ability to synthesis of materials with different structure and favorable properties that can be used in different applications [49, 54], such as: Sol-gel method provides an alternative route for the production of ceramics and glasses [57]. Sol-gel process offers new approaches to synthesis of fine powders [67]. The ability of the sol-gel process to form extremely pure metal oxides leads to their use for the production of optical materials such as lenses [68]. Films and coatings represent the earliest use of sol-gel processing [67]. One of the most important applications of the sol-gel method is in the field of production of porous materials which they have been used as filters on a sub-micrometer scale with applications in waste water treatment [69]. The addition of optically active ions as a gust (rare earth ions) into the porous material which they are synthesized via sol-gel method leading to fabricate solid state laser [70].
2.8 Sol-Gel Processed Laser The sol-gel method has been used extensively to obtain novel optical materials with luminescent properties which attracted renewed interest due to their advantages. These valuable materials are suitable for the development of solid-state photonic devices basing on incorporating of lanthanide (as a dopant) into crystal or vitreous host, as shown in figure (2-10). These systems can be easily prepared in different shapes and sizes with uniform distribution and different concentrations of rare earth ions. The most remarkable feature of
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Chapter Two
Theoretical Background
the rare earth ions in solid state host is the sharpness of their absorption and emission spectral lines, and they assumed as a good light emitters in the spectral region covering visible, near infrared (NIR), and infrared (IR) up to 3μm regions [71].
Fig. 2-10: Entrapment of dopant (guest) into a sol-gel network (host) [57].
2.8.1 TiO2 Laser Host 2.8.1.1 Structure of TiO2 In recent years, intense focusing on the preparation of metal oxide nano crystals has been increased, owing to their markedly different physical and chemical properties with respect to bulk materials. One of the most interesting nanomaterial is titanium dioxide (TiO2), commercially called ''titania'' ; it belongs to the family of transition metal oxides, it has fascinating properties and various applications which had being researched actively and widely in different studies [72, 73]. In general, TiO2 structure exists in both amorphous and crystalline forms, its main crystalline phases are: anatase, rutile and brookite [21]. The anatase phase of TiO2 is a metastable phase, and converts to stable rutile phase during annealing, at the temperature of 600-700 oC. Some researchers have also found the rutile structure at 500 oC, and some have found it at annealing temperature of more than 800 oC. It is also known that the transformation characteristics from anatase to rutile phase strongly depend on
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Chapter Two
Theoretical Background
thermal treatment and impurity effect. Marked increase in particle size was noticed in the 600-1000 oC region, generally the crystallite size increases rapidly after 600°C [74]. Both anatase and rutile phase of titania have tetragonal structure, while; brookite phase has orthorhombic structure, as shown in figure (2-11).
Anatase
Rutile
Brookite
Ti
Ti
O
O
Fig. 2-11: Unit cells of three different phases of TiO2 nanocrystal [75].
2.8.1.2 Properties of TiO2 Generally, titanium dioxide has numerous properties which attracted a vast attention, and make it to be widely studied, such as [27, 37, 76]: Optical property: one of the recognizable properties of TiO2 is transparent in the visible and infrared region while it absorb in the ultraviolet region. So it is a prominent candidate as host material of rare earth ions for preparing the active medium of a solid state laser.
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Chapter Two
Theoretical Background
Electrical property: due to its high dielectric constant, it can be used as a dielectric material in electronic application. Mechanical property: it posses hardness, low density and high durability. Chemical property: it has high chemical stability and good resistance to chemical erosion. Other properties: it is identifiable by non-toxicity and safety toward humans and the environment, cheapness, easily synthesized and handled.
2.8.1.3 Applications of TiO2 TiO2 nanomaterials are known for their numerous and diverse applications, since it has the above mentioned properties, demands on manufacturing this notable oxide has increased for using it in different applications, including: TiO2 has a high refractive index (a measure of the ability to bend light), so it used as a white pigment to provide whiteness and opacity in the products such as: paint, papers, ointments and tooth paste [21]. TiO2 nanomaterials have high absorption in the UV region, so it is suitable to use in the UV protection applications and cosmetic products [77, 78]. TiO2 has high resistance towards acid and alkali makes it suitable in medical applications for artificial bone or tooth fabrication [64]. Due to its high dielectric constant, TiO2 thin films have been widely investigated for applications in micro-electronic devices [79]. TiO2 is extensively used for the purpose of protective coatings [77]. Since TiO2 posses good optical properties which mentioned above, so it is suitable to use in the optical devices [35]. (11)
Chapter Two
Theoretical Background
2.8.2 Dopant Ions 2.8.2.1 Rare Earth Ions Lanthanide group consists of 15 elements which have atomic number ranging from 57 to 71, starting with lanthanum (La), and ending with lutetium (Lu), with the inclusion of scandium (Sc) and yttrium (Y) which belongs to the same group, whole of these 17 elements are referred to as the rare earth elements (RE) [10], the electronic configuration of these elements and their trivalent ions are shown in table (2-1). Table 2-1: Electronic configuration of rare earth elements and their trivalent ions [10].
The trivalent ions of the lanthanide series are characterized by a gradual filling of the 4f orbitals, from 4f0 (for La3+) to 4f14 (for Lu3+). Since the 4f shell is unfilled with the required number of electrons, some of the 4f-states are still empty and the transitions of the 4f electrons to the empty states can
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Chapter Two
Theoretical Background
occur as a result of light absorption. Lanthanide ions can emit light with different colors; as an example, Eu3+ emits red light, Tb3+ green light, Sm3+ orange light, and Tm3+ blue light, in the visible spectral range. On the other hand Yb3+, Nd3+, and Er3+, Pr3+, Sm3+, Dy3+, Ho3+, and Tm3+ are known for their near-infrared luminescence [71].
2.8.2.2 The Trivalent Holmium Ions (Ho3+ Ions) Holmium (Ho) is the eleventh element in the family of the lanthanide group; some properties of it are listed in table (2-2).
Table 2-2: General properties of holmium atom [80]. Symbol
Ho
Atomic number
67
Atomic weight
164.93
Standard state
Solid at 25 ºC
Group name
Lanthanoide
Block in periodic table
f-block
Color
Silvery white
Melting point
1472 ° C
Boiling point
2695 °C
Electron configuration
[Xe]4f116s2
Oxidation state
3+
The trivalent ion (Ho3+), is a common ion of Ho atom with the electronic configuration [Xe] 4f10. In general, the 4f shell is filled with 14 electrons. 4f shell of Ho3+ ion contains only 10 electrons, so it remains unfilled, this means that the electrons in the 4f shell are optically active and perform transitions between its energy levels as a result of light absorption, its (11)
Chapter Two
Theoretical Background
partial energy levels diagram depicted in figure (2-12). Due to its favorable energy level structure, it is one of the most attractive candidates for dopant into a host material among rare earth ions. It shows strong emission at various wavelengths including the visible and near infrared region. Unfortunately, the choice of host lattices for this ion is limited. This is due to the fact that close spacing of the energy levels in Ho3+, this ion is prone for strong multiphonon decay. Therefore Laser operation was mostly realized by employing low phonon host crystals.
Fig. (2-12): Partial energy levels diagram of Ho3+ ion [81].
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Chapter Two
Theoretical Background
2.8.2.2.1 Visible Emission of Ho3+ Ions In this sub-section, the ability of Ho3+ ions in different hosts for emission in the visible spectral range will be explained basing on the previous studies. According to the study of Fabian Reichert (2013) [82], Ho 3+ doped into a crystalline host of fluoride material occurs trivalent with the electronic configuration [Xe] 4f11. The 4f11 configuration consists of 41 manifolds with 5
I8 as the ground state, 5I6 and 5I7 as the long-lived metastable state, 5S2 as the
upper laser level, and 5F3 as the pumping level. Under two different excitations of 450 nm and 480 nm, strong absorption bands corresponding to these two transitions (5I8→5F1, 5G6), (5I8→5F3) respectively observed. Since the distance between the upper laser level 5S2 manifold and the pump level 5F3 is approximately 1900 cm-1, sufficiently high phonon energies can cause a fast non-radiative decay, resulting an efficient population process for the 5S2 manifold. The energetic distance towards the 5F5 multiplet, which is the next energetically lower level, is approximately 3000 cm -1, the phonon spectrum of the host systems has to be taken into account to prevent a pronounced non-radiative decays, from the 5S2 manifold, lasing emission obtained via these two transitions: 5S2→5I8 in the green region through CaF2 host at a temperature of 77 K and 5S2→5I7 in the deep red region through LiYF4 at 90 K and YAlO3 at room temperature, as shown in the figure (2-13).
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Chapter Two
Theoretical Background
6
Fig. 2-13: Schemes of energy level of Ho3+ ion [82]. radiative transition represented by colored arrows, and non-radiative transition represents by black arrows.
2.8.2.2.2 Near-Infrared Emission of Ho3+ Ions As mentioned before, Ho3+ ion is known for its ability to emit in the near infrared (NIR) spectral region in the host materials. Generally, this long wavelength laser has valuable application in surgical field, as eye safe laser. According to the study of Stouwdam J. (2004) [11], when Ho3+ ions doped with the two different hosts LaF3 and LaVO4. Under excitation of 450 nm, emission could be detected at 966 and 1460 nm from 5F5→5I7 and 5F5→5I6 transitions respectively. The absorption and emission spectra are shown in figure (2-14) and (2-15) respectively.
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Chapter Two
Theoretical Background
From figure (2-15), it is clear that; the emission of Ho3+:LaVO4 system was weaker than Ho3+: LaF3 system, which could be a result of the higher phonon energies of the LaVO4 host material which behaves as a factor for quenching of its emission.
Fig. 2-14: Absorption spectra of Ho3+ doped LaF3 and LaVO4 nanoparticles [11].
Fig. 2-15: Near infrared emission spectra of Ho3+ doped LaF3 and LaVO4 nanoparticles [11].
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Chapter Two
Theoretical Background
2.8.2.2.3 Up Conversion Emission of Ho3+ Ions It is known that certain glasses and crystals that contain trivalent lanthanide (Ln3+) ions such as Ho3+ can convert infrared radiation to either visible or ultraviolet light through a process called upconversion. The process involves exciting lower lying energy levels with low energy radiation (such as red, or (NIR) radiation), resulting in emission at shorter wavelengths (in the visible or near UV range) from higher electronic levels. The absorption of at least two photons is required to provide sufficient energy for upconverted emission to occur. Trivalent holmium ion (Ho3+) is a good candidate for upconversion processes because it has many long-lived metastable levels such as (5I6 and 5I7) from which excited state absorption (ESA) can take place. There are also several high-lying levels such as (5G4, 3K7) and [(5F3), (5F4, 5S2)] that can give rise to transitions at various wavelengths in the UV and visible regions [83,84]. 2.8.2.2.4 Resonance Fluorescence Process of Ho3+ Ions It is a special case of fluorescence emission process in which absorption and emission process occurs between same two levels in an atom or ion, which causes overlapping between the absorption and emission spectra, therefore no emission be observed.
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Chapter Three
Experimental Setup and Sample Preparation
Chapter Three Experimental Setup and Sample Preparation
3.1 Introduction This chapter explains the overall experimental details that are essential for gathering the data to carry out this study. In general each experimental study can be divided into two stages; the first stage is the selection of the chemical raw materials, calculating their required amounts, and mixing them to provide starting material which is ready for initiating the preparation of the sample. Surely, the selection of a good method for sample preparation is an important step in experimental study. In this work, sol-gel method had been used for synthesizing of pure and Ho3+ doped TiO2 nanopowder and rod. As the name implies, sol-gel process involves transition from liquid phase (sol) into solid phase (gel) by a number of chemical reactions not far above room temperature. The processing steps of synthetic method have a significant role in determining the quality of the final product. Characterization of the prepared sample, in order to obtain information about it, and knowing its behavior can be assumed as the second stage of the experimental study. Generally; these characterizations become a fingerprint of the synthetic sample. In the present study, the following techniques which depicted in table (3-1) are used for analyzing the prepared samples.
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Chapter Three
Experimental Setup and Sample Preparation
Table 3-1: Analyzing instruments for characterizing the synthetic samples. Used Device 1-X-ray diffractometer
Purpose of use
Notes
For studying the structure of
SHIMADZU, JAPAN, XRD-6000
the prepared samples
With cukradiation ( 1.54060 Å)
(XRD) 2- Fourier Transform
For studying the composition
Infrared spectrometer
and chemical bonding of the
(FTIR)
prepared samples
3-UV/Visible
For measuring the absorbance
spectrophotometer
spectra of the prepared samples
4-Spectrofluorophotometer
Thermo fisher- Nicolet- IS-10
Shimadzu-1800-Spectrophotometer
For measuring the fluorescence
Shimadzu-Spectrofluorophotometer
spectra of the prepared samples
RF-1501
The practical steps of this study can be summarized as:
Sample preparation
Optical characterization Calcination of samples
Absorbance characteristics Fluorescence emission characteristic
Structural characterization
XRD- technique FTIR- technique Fig. 3-1: Flowchart of the practical steps followed in this study.
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Chapter Three
Experimental Setup and Sample Preparation
3.2 The Chemical Materials 3.2.1 Sol-Gel Precursor The main precursor (starting precursor) for the preparation of pure and Ho3+ doped TiO2 samples is the titanium tetra iso-propoxide [Ti(OPri)4]. 3.2.2 Solvent Ethanol (EtOH) of spectroscopic standard had been used for diluting Ti(OPri)4. 3.2.3 Other chemical material 3.2.3.1 Deionized Water It was used for hydrolyzing of Ti(OPri)4 during hydrolysis reaction. 3.2.3.2 Hydrochloric Acid (HCl ) It was used as a catalyst for hydrolysis reaction; also it behaved as a deflocculating agent in the reactions. General properties of the above mentioned chemicals are shown in table (3-2). 3.2.4 Active Rare Earth Ions Holmium ion (Ho3+) in the form of holmium (III) chloride hydrate was used as doping ions to prepare Ho3+ doped TiO2 samples. Some properties of the used holmium ions listed in table (3-3).
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Chapter Three
Experimental Setup and Sample Preparation
Table (3-2): General properties of the used chemical raw materials.
Raw Materials
Molecular Formula
Molecular Weight
Titanium TetraIsopropoxide
C12H28O4Ti
Ethanol
C2H5OH
Molecular Structure
Density
Purity
State
284.26 g/mol
0.96 g/cm3
Purm (≥98%)
LightYellow liquid
Fluka
46.07 g/mol
0.785 g/cm3
99.9%
Liquid
Scharlau
Liquid
H.KERN DL GmbH
Liquid
Merck
Deionized Water
H2O
18 g/mol
1 g/cm3
high degree of purity (empty of additional ions)
Hydrochloric Acid
HCl
36.46 g/mol
1.19 g/cm3
37%
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Supplier
Chapter Three
Experimental Setup and Sample Preparation
Table (3-3): General properties of Ho3+ ions. HoCl3.xH2O
Molecular Formula
Molecular Weight
271.29 g/mol (anhydrous)
Appearance
Crystalline chunks
Color
Light Pink
Supplier
IRAQ Biotech
3.3 The Glassware Apparatus During the preparation of samples, these apparatuses were used to measure the volume of the required raw materials for sol preparation. Beakers Round flask bottom Pipettes Burette After using above glassware during sample preparation, it was necessary to wash them by sulphuric acid (H2SO4) for eliminating any residual precipitation resulting from the expose of (TTIP) to air.
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Chapter Three
Experimental Setup and Sample Preparation
3.4 Other Used Instruments Sensitive balance: used for weighting of holmium chloride. Heating unit: used for evaporation of solvents in the composition of the prepared sol. Programmable Muffle furnace: used for densification of the prepared samples.
3.5 The Preparation System In order to prepare pure and Ho3+ doped TiO2 samples, the preparation system had been built for such purpose in department of physics/college of education/university of Sulaimani, as it shown in figure (3-2). The preparation system consists of:
3.5.1 The Heater/Chiller Unit In general, this unit consists of four main parts: Heater Chiller Thermostat Water pumps
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Chapter Three
Experimental Setup and Sample Preparation
3.5.2 The Reactor Setup This unit consists of the following parts, as shown in figure (3-3). Water Jacket Reaction Chamber (round flask bottom) Burette and its holder The magnetic stirrer: which was used for stirring the contents (precursors) inside the round flask bottom. 3.5.3 The Hood It was used to draw out the residual gases that were produced from the chemical reactions.
Heater/chiller Unit
Water pumps
Thermostat
Fig. 3-2: Samples preparation system. (38)
Chapter Three
Experimental Setup and Sample Preparation
Burette
Reaction chamber (Round flask bottom) Water Jacket
Magnetic stirrer
Fig. 3-3: The reactor setup.
3.6 Raw Materials Volume Calculation Before mixing all the precursors for preparing TiO2 sol which then becomes TiO2 gel, the required volume of them must be measured as a starting step.
Number of moles of chemical materials can be measured through this
equation:
n W M
.....(3 1)
w
Where: n: is the number of moles (mol). W: is the weight of chemicals (g). Mw: is the molecular weight of chemicals (g/mol). (45)
Chapter Three
Experimental Setup and Sample Preparation
Equation (3-2) can be used for calculating of the corresponding volumes of these weights.
…… (3-2)
Where: V: is the required volume (ml). : is the density of the chemicals (g/cm3).
3.7 Sample Preparation 3.7.1 Preparation of Pure TiO2 Sol As discussed before, steps of sample preparation have a great role in selecting the quality of the final product. In this work, sol-gel method has been successfully used to prepare clear solution without coagulation. Here, we must prepare two solutions which we named them as solutions (A and B). Steps of preparation of both of them include: Preparation of solution (A): half of the prescribed amount of anhydrous ethanol (C2H6O) was used for dilution of titanium tetra-iso-propoxide (TTIP) in a glass beaker, then this mixture was transferred to round flask bottom. Preparation of solution (B): the addition of the specified amount of deionized water and hydrolcloric acid (HCl) to another half of the ethanol in a glass beaker, this mixture was transferred to a burette.
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Chapter Three
Experimental Setup and Sample Preparation
After the preparation of both solutions, solution (B) was added drop by drop (to prevent turbidity) to solution (A) under continued stirring. These steps were carried out in a cooler water jacket for cooling the final solution by water at temperature approximately (19-24) C. The molar ratio of the used chemical materials TTIP: H2O: EtOH: HCl was 1: 1: 10: 0.1 [85]. The whole process is summarized in figure (3-4).
Fig. 3-4: Scheme of pure TiO2 sample preparation by sol-gel method. (45)
Chapter Three
Experimental Setup and Sample Preparation
3.7.2 Preparation of Ho3+ Doped TiO2 Sol Holmium ions (Ho3+) in the form of holmium chloride with a crystalline chunk had been used as a doping ion precursor. The procedure of the doped TiO2 sol preparation is similar to the procedure of the preparation of pure TiO2 sol as mentioned in the previous section, but there was a small difference in division of ethanol (EtOH) in this form: The first half of the ethanol was divided in to two parts, the first part was used for dilution of (TTIP), and this solution was named as solution (A1). The second half was mixed with the dopant precursor (1, 3, 5, and 7 wt%), this solution was named as solution (A2). Then, the solution (A2) was added to solution (A1) which was led to form a yellowish solution named as solution (A). On the other side, the specified amount of deionized water and hydrochloric acid (HCl) was added to the second half of ethanol (EtOH) which was named as solution (B). Then solution (B) was added drop by drop to solution (A) under continuous stirring. The final solution represented Ho3+ doped TiO2 solution. The whole process is summarized in the figure (3-5).
(44)
Chapter Three
Experimental Setup and Sample Preparation
Fig. 3-5: Scheme of Ho3+ doped TiO2 sample preparation by sol-gel method.
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Chapter Three
Experimental Setup and Sample Preparation
3.8 Heating the TiO2 Sol After the preparation of the pure and Ho3+ doped TiO2 sol, it was introduced into a heating unit at temperature of 60 oC for 1 h for starting evaporation of solvents which presence in the composition of the titania sol.
3.9 High Temperature Treatment of the Wet Gel After heating the undoped and doped TiO2 sol, it was necessary to leave them inside a container until it was transferred into a viscoelastic body, called ''wet porous gel''; then this wet body was calcined at 500 C for 1 h in a furnace for closing its pores and densifing it. The result of this calcination step was obtaining a powder. The pure and doped powder samples were subjected to a number of techniques such as (XRD), and (FTIR) for characterizing them.
3.10 Structural Characterization Calculation of the Prepared Sol-Gel Samples The effect of Ho3+ ions addition on the TiO2 lattice can be observed via calculating of lattice constant of the doped samples with respect to the pure sample. During the calcination step of the gel, it was converted from amorphous phase to crystalline anatase phase, this phase has a tetragonal structure with the lattice parameters 'a' and 'c' which was determined by choosing two appropriate (hkl) reflections of (101) and (200), via the following equations [86]:
1 h 2 k 2 l2 2 2 d2 a c
….. (3-3)
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Chapter Three
Experimental Setup and Sample Preparation
Where: d: is a plane-spacing in a crystal, and its value can be measured from the 2-angle by Bragg's law [86]: ….. (3-4)
λ =2dsin θ d
λ 2 sinθ
….. (3-5)
: is the wavelength of x-ray which equal to (1.54060 Å). Combining equations (3-3) and (3-5), we obtain:
sin 2θ
λ 2 h 2 k 2 l2 ( 2) 4 a2 c
.....(3 - 6)
On the other hand, the grain sizes (t) of pure and doped TiO2 nanopowder were estimated by using Scherer's formula, equation (3-7) [86]:
t
0.9 λ B cos(θ B )
….. (3-7)
Where: B: is the Full Width at Half Maximum (FWHM) of the peak, which equal to (1-2) (in radian). B: is the Bragg's angle (in degree) 1 radian=57.29578.
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Chapter Four
Results and Discussion
Chapter Four Results and Discussion
4.1 Introduction The exploration of a new material through any experimental study requires a number of sequential steps for the preparation of sample by suitable method and testing it via different techniques in order to characterize it and obtaining its properties. In this chapter, we will present the best results which were obtained from the structural and optical characterizations of the prepared samples throughout this study and discussing them in detail. The investigation of results which obtained from testing techniques is an important point in deciding the quality of the synthetic product and succession of the preparation method that used in this study.
4.2 Appearance of the Prepared Alkoxide Solution and Samples After mixing the initial raw materials and occurring a series of hydrolysis and condensation reactions, a clear yellowish pure and doped sol was obtained. The formation of sol is a starting point of sol-gel process which leads to conversion into a gel at the gel point, then obtaining a final product after some heating steps. In this study, (TTIP: H2O: EtOH: HCl) chemicals were mixed with this molar ratio (1: 1: 10: 0.1) [85], for preparing TiO2 samples as a host, as discussed in 3.7.1 and 3.7.2., with different concentrations of the gust ions ( Ho3+ ions) such as (1, 3, 5, and 7) wt%.
)79)
Chapter Four
Results and Discussion
The prepared pure and Ho3+ doped sol had been kept inside the tube with covering it for a long time (approximately two month) to avoid exposing to air, this led to obtaining a transparent pure and doped rod (small bulk), as shown in figures (4-1) and (4-2).
Fig. 4-1: Photograph of pure TiO2 rod.
Fig. 4-2: Photograph of 7 wt% Ho3+ doped TiO2 rod.
)7:)
Chapter Four
Results and Discussion
4.3 Characterization of Samples 4.3.1 Structural Characterization of Pure and Ho3+ Doped Titania samples 4.3.1.1 X-Ray Diffraction Analysis (XRD) X-Ray diffraction (XRD) is a technique used for identification of the crystal structure, grain size, and lattice parameters of the prepared samples. All pure and doped samples with different concentration of Ho3+ ions calcined at 500 oC for (1h) before analyzing, as shown in figure (4-3).
Fig. 4-3: Photograph of the pure and doped TiO2 nanopowdered samples.
Results showed that both pure and doped TiO2 nanopowder had crystalline anatase structure corresponding to (101), (004), (200), (105), (211), (204), (116), (220), and (215) diffraction peaks respectively, referring to standard (ICDD:N 1997 JCPDS-International Center for Diffraction Data; PCPDFWIN V.1.3). Figures [(4-4)-(4-8)] show these results. No peak of rutile phase can be detected, this is clearly depicted that anatase was the main crystalline phase of pure and doped TiO2 nanopowder, the results were in a good agreement with [8, 13, 87]. The intense sharp peaks indicated that the crystalline phase of anatase TiO2 was successfully formed [2]. )7;)
Chapter Four
Results and Discussion
It can be noted that; there is no appreciable difference in the obtained spectra of our samples compared with those reported previously, and this indicates to the success of sample preparation process via controlling all experimental parameters.
400 (101)
350
250
(215)
(220)
(116)
100
(204)
(105)
150
(211)
(200)
200 (004)
Intensity (a.u)
300
50 0 0
10
20
30
40
50
60
70
80
90
2qo
Fig. 4-4: XRD patterns of pure TiO2 nanopowder calcined at (500C).
400 350 Intensity (a.u)
300 250 200 150 100 50 0 0
10
20
30
40
50
60
70
80
90
2qo
Fig. 4-5: XRD patterns of 1 wt% Ho3+:TiO2 nanopowder calcined at (500C).
)86)
Chapter Four
Results and Discussion
400 (101)
350 250 200 150
(220)
Intensity (a.u)
300
100 50 0 0
10
20
30
40
50
60
70
80
90
2qo
Fig. 4-6: XRD patterns of 3 wt% Ho3+:TiO2 nanopowder calcined at (500C).
400 (101)
350 250 200 150
(116)
(211)
Intensity (a.u)
300
100
50 0 0
10
20
30
40
50
60
70
80
90
2qo
Fig. 4-7: XRD patterns of 5 wt% Ho3+:TiO2 nanopowder calcined at (500C).
400 350 250 200 150
(116)
(211)
Intensity (a.u)
300
100 50 0 0
10
20
30
40
50
60
70
80
90
2qo
Fig. 4-8: XRD patterns of 7 wt% Ho3+:TiO2 nanopowder calcined at (500C). )86)
Chapter Four
Results and Discussion
The reason for disappearing rutile phase in prepared samples belong to two factors: the first is Ho3+ doping effectively had inhibitory effect on the transformation from anatase to rutile phase, the inhibition of the phase transition might be ascribed to the stabilization of anatase phase by the surrounding rare earth ions (Ho3+ ions) through producing Ti-O-Ho interaction. The second is the calcination temperature which was (500 oC) in this study that was not enough for the phase transformation from anatase to rutile, since the anatase start to convert to rutile above the temperature of 500 o
C [13]. From figures of the doped samples, it could be seen that no
characteristic peaks of Ho3+ ions was found in the XRD patterns, this may be due to the dopant concentration which was relatively low for XRD to reveal, this shows the incorporation of Ho3+ ions into TiO2 crystal structure without formation of the secondary phase, despite the difference of the ionic radii of both Ti4+ and Ho3+ ions (0.605 Ao and 0.901 Ao) respectively [13, 30, 88], these results were in agreement with Hong et.al [88], on the other hand; most of the Ho3+ ions were expected to locate in the grain boundary or more porous region in TiO2 structure [13]. The tetragonal bravais lattice type of the polycrystalline anatase TiO2 powder was verified by lattice constant calculation from diffraction peaks in figures [(4-4)-(4-8)]. Based on the planes of the anatase phase (101) and (200), the lattice constants 'a' and 'c' of the titania host can be calculated via equation (3-6). After determination both 'a' and 'c' for pure and all doped samples, it was obtained that; the dopant ions cause lattice distortion of the host. By increasing the concentration of the doping ions the values of 'a' was approximately constant, while there was a random change in the value of 'c' as shown in table (4-1).
)86)
Chapter Four
Results and Discussion
Changing the value of 'c' belongs to the fact that although there is a mismatching between the ionic radii of both Ti4+ and Ho3+ ions (As mentioned above), certain Ti ions were replaced by Ho ions in the TiO2 lattice (substitutionally) and forming Ti-O-Ho bond, which resulted in distortion and expansion of the crystal lattice [89], as shown in figure (4-9). 12 10 Lattice constant (Ao)
c 8 6
a
4 2 0 0
1
2
3
4
5
6
7
8
Ho3+ concentration (wt% in TiO2 )
Fig. 4-9: Lattice constant of TiO2 nanopowder calcined at (500C) as a function of Ho3+ concentration.
The grain size (t) of both pure and doped TiO2 nanopowder estimated from (101) plane of anatase phase by using Scherrer's formula equation (3-7), are listed in the table (4-1) and shown in figure (4-10). The random change in grain size of the doped nanopowder during the increase of the dopant concentrations into a host with respect to the pure nanopowder as a reference, can be explained as: The calculated grain size (t) of the pure nanopowder was 14.3 nm which was increased to14.9 nm for 1 wt% Ho3+ doped nanopowder, this may be attributed to this small amount of the dopant ions which was not entered the structure of TiO2 lattice and located on its surface which leads to the crystal growth and increasing its grain size. When the concentration of the )86)
Chapter Four
Results and Discussion
dopant ions increased to 3 wt%, the grain size of TiO2 was reduced to 13.3 nm, this may be due to the fact that some amount of the dopant ions entered the structure of TiO2 substitutionally and forming Ti-O-Ho bonds which inhibit the growth of the TiO2. By increasing the concentration of the dopant into 5 wt%, more amounts of the dopant ions entered the TiO2 crystalloid and forming more Ti-O-Ho bonds which retarded contacting of particles, led to the increase of the inhibition in the growth of the grain size into 11.6 nm. Finally, the maximum concentration of the dopant ions 7 wt% caused clustering of part of dopant ions in the pores of titania, and the other part of the dopant may enter the TiO2 crystalloid substitutionally. While some amount of them may locate on the surface of TiO2 which enhance the increasing of the particle size to 12 nm comparing with 5 wt%.
20 18 16 Grain size (nm)
14 12 10 8 6 4 2 0 0
1
2
3
4
5
6
7
8
Ho3+ concentration (wt% in TiO2 )
Fig. 4-10: Grain size of doped TiO2 nanopowder calcined at (500C) as a function of Ho3+ ion concentration.
)86)
Chapter Four
Results and Discussion
Table 4-1: Grain size and lattice constants of pure and doped TiO2 nanopowder with different concentration of Ho3+ ions. Ho3+ ions concentration ( wt %)
a (Ao)
c (Ao)
Grain size (t)(nm)
0
3.784
9.437
14.302
1
3.791
9.594
14.929
3
3.784
9.353
13.393
5
3.788
9.539
11.664
7
3.795
9.488
12.004
4.3.1.2 Fourier Transform Infrared Spectroscopy (FTIR) Analysis Infrared spectroscopy is the study of the interaction of infrared (IR) radiation with matter. When IR radiation interacts with the prepared sample, some of it absorbed by the sample and some of it is passed through (transmitted). The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample. Like a fingerprint no two unique molecular structures produce the same infrared spectrum, so it can be use to determine the consistency of a sample. After performing thermal treatment for the prepared pure and doped titania samples at 500 oC for 1 h, they became a powder as shown in figure (4-3). Finally, they were introduced into FTIR device for analyzing their composition. The FTIR spectra of both pure and doped powder are depicted in figure (4-11).
)87)
Chapter Four
Results and Discussion
2881.67
7wt%
2879.27
5wt%
2876.34
3wt%
3002.12
1wt%
2900.31
3646.89
Pure
Fig. 4-11: FTIR spectra of pure and Ho3+ doped TiO2 nanopowder.
Different IR bands were observed for pure TiO2 nanopowder as shown in figure (4-11), represent an existence of different functional groups, can be explained as below: The band observed at 657.44cm-1 was corresponded to Ti-O bonds, and bands located at 1066.13 cm-1 was attributed to Ti-O-Ti linkage in TiO2 nanopowder, this was in agreement with [90], the existence of these bonds in the titania network indicate that condensation reaction successfully completed.
)88)
Chapter Four
Results and Discussion
A small band with very low intensity appeared at about 1651.87 cm−1 which was assigned to H-O-H bending vibrations of physically adsorbed water, while the band peaking at 3646.89 cm-1 belongs to stretching vibrations of OH– group located on the surface of titania [89]. The presence of carbon was impossible to avoid completely since the samples were prepared in organic media, therefore two bands with too low intensities centered at 1715.65 cm-1, and 2350.74 cm-1 were due to C=O and vibration respectively, which indicated the formation of carbonate species through the decomposition of organic compound [87, 91]. On the other hand, very small band found approximately at 2900.3cm-1 represented C-H vibration of alcohol [90, 92], the weakness of intensity of these bands showed that the alcohol molecules were well evaporated during calcinations step at 500oC. In order to understand the role of the dopant ions in the titania network, a comparison between doped samples spectra with respect to pure sample spectrum must be done, as shown in figure (4-11). Bands observed in the spectra of the doped samples are similar to these bands that observed in the spectrum of the pure sample with notable differences in their intensity; these differences are due to the existence of the dopant ion as explained bellow: In the finger print region of the Ho-doped samples, the characteristic bands which belongs to titania become slightly sharpened, which may be on account of the formation of Ti-O-Ho bonds [93]. Unlike the XRD spectra of the doped samples, in the FTIR spectra of the doped samples some bands observed related to the presence of Ho3+ ions with different concentrations, two bands with very low intensity located at (1338, and 1339) cm-1 in the FTIR spectra of both (3, and 5) wt% doped samples which represented the presence of Ho3+ ions in the structure of TiO2 )89)
Chapter Four
Results and Discussion
nanopowder, and approximately high intense band appeared in the same location of the spectrum 7 wt% doped titania sample while this band is not appear in 1 wt% doped titania spectrum, relating to low concentration of the dopant ion which is not enough to be detected by used FTIR device [94] . Weak bending vibration bands of H-O-H of physically adsorbed water in all doped samples locating at 1652cm-1, and 1653 cm-1, while low intensity bands which represent stretching vibration of OH– group located on the surface of titania in (1, and 3) wt% doped samples and approximately strong bands for both (5 and 7) wt% doped samples were observed approximately at 3648 cm-1 comparing to the pure sample, this indicated that Ho3+doped TiO2 had a higher ability of absorbing water than pure TiO2, which resulted in more hydroxyl on the surface of Ho3+doped TiO2 samples[13]. These two bands that represent C=O and
vibration of carbonate
species which formed through the decomposition of organic compound were observed at 1716 cm-1 and 2358 cm-1 respectively for all doped samples, also bands represented C-H vibration of alcohol located at (2881-3002) cm-1 in the spectra of all doped samples have higher intensity comparing with the pure sample, this may due to locating part of the dopant ions on the surface of titania, or clustering it in the pores of titania which inhibit completely release of organic residue during calcination step. The whole above mentioned ranges are depicted in the table (4-2).
)8:)
Chapter Four
Results and Discussion
Table 4-2: Infrared bands position of pure and Ho3+doped titania nanopowder with different concentration of the Ho3+ dopant ions.
IR band position (cm-1)
Samples
Ti-O
Ti-O-Ti
vibration
Vibration
Pure TiO2
1 wt% Ho3+ TiO2
3+
Ho ions vibration
1066.13
667.84
893.95
751.11
1078.46
O-H stretching
C-H vibration of alcohol
C=O vibration of alcohol
vibration of alcohol
1715.65
2350.74
2900.31
1716.32
2358.76
3002.12
1716.82
2359.12
1716.74
2358.88
2879.27
1716.71
2358.23
2881.67
1651.87/
---657.44
H-O-H bending /
3646.89
1652.69/
----
3648.15
1170.58
3 wt% Ho3+ TiO2
667.81
894.52
752.31
1057.39
1653.03/ 1338.93 3648.43
2876.34
1189.30 5 wt% 3+
Ho
TiO2
7 wt% Ho3+ TiO2
668.26
894.61
754.25
1045.12
668.33 756.06
1652.96/ 1339.05 3648.26
894.75 1089.13
1652.97/ 1339.27 3648.39
1186.04
)8;)
Chapter Four
Results and Discussion
4.3.2 Optical and Spectroscopic Characterization of Pure and Ho3+ Doped Titania Samples The optical properties of RE ions arise mainly from the transitions between the different 4f
n
energy states, where (n) denotes the number of
electrons on the 4f subshell. The rare earth ion in the ground state may be excited to a higher energy state if it absorbs light having energy equivalent to the energy difference between the ground state and that particular excited state. Moreover, there is a possibility that the ion in the excited state may relax back to the lower energy levels via emission with energy equivalent to the energy difference between the two levels. In this study, pure and different concentrations of Ho3+ doped TiO2 gel had been prepared; their optical and spectroscopic characteristics were obtained via absorption and fluorescence emission spectra.
4.3.2.1 Absorption Spectra In order to show the absorption property of pure and Ho 3+ doped TiO2 gel, absorption measurement were carried out at room temperature, using (UV/Vis spectrophotometer). The obtained absorption spectra is illustrated in figures (4-12) and (4-13).
)96)
Chapter Four
Results and Discussion
2 1.8 1.6
Absorbance (a. u.)
1.4 1.2 1 0.8 0.6 0.4 0.2 0 400
450
500
550
600
650
700
750
800
wavelength (nm)
Fig. 4-12: Absorption spectra of pure TiO2 gel. 1 1 wt% Ho3+
0.9
3 wt% Ho3+
0.8
5 wt% Ho3+
Absorbance(a.u.)
0.7
7 wt% Ho3+
0.6 0.5 0.4 0.3 0.2 0.1 0 400
450
500
550
600
650
700
750
800
Wavelength (nm)
Fig. 4-13: Absorption spectra of different concentration of Ho3+ doped TiO2 gel.
By observing the resulted spectrum of the pure sample in figure (4-12); there is no any peak, this indicates that the pure TiO2 does not absorb in the visible region. While three obvious absorption bands can be observed in the spectra of (3, 5, and 7) wt% Ho3+doped samples, peaking at (450, 539, and 644) nm corresponding to (5I8→5F1,5G6), (5I8→5F4,5S2) and (5I8→5F5) transitions respectively, as shown in figure (4-13). But for 1 wt% Ho3+ doped sample, there was no any absorption peak at both (450 and 539) nm excitation )96)
Chapter Four
Results and Discussion
wavelengths. This shows that, these excitation wavelengths may not excite this small amount of the Ho3+ ions well, therefore; it does not have any emission. The absorption spectra of the prepared samples are in agreement with the resulted absorption spectra of [82, 95]. Also, from figure (4-13), it is clear that; by increasing the concentration of Ho 3+ ions, the intensity of the bands has been increased; this may belong to the contribution of more amounts of Ho3+ ions in the absorption process of excitation wavelength.
4.3.2.2 Fluorescence Emission Spectra In order to represent fluorescence emission ability of Ho3+ doped TiO2
samples,
fluorescence
measurement
were
carried
out
using
Spectrofluorophotometer, and Xenon lamp (Xe-150 Watt) for excitation process. Three different excitation wavelengths was used according to absorption spectra which they were (450, 539, and 644) nm. In the case of excitation wavelength peaking at 450 nm, different emission bands could be observed for different concentrations of Ho 3+ ions doped TiO2 sol-gel prepared host. These bands were locating at (524, 508, and 529) nm for (3, 5, and 7) wt% dopant concentrations corresponding to (5F4, 5S2→5I8), (5F3→5I8), and (5F4,5S2→5I8) respectively as depicted in figures (4-14), (4-15) and (4-16), these results are in agreement with [29, 83]. On the other hand, these results agreed with our FTIR results, in which the small amount of 1 wt% Ho3+ ions was not appeared in the FTIR spectra, belonging to the lack in the amount of Ho3+ ions which may not be detected by the testing device (as mentioned before). Resulted spectra indicate that, prepared Ho3+doped TiO2 samples via sol-gel method can be used as a laser active medium.
)96)
Chapter Four
Results and Discussion 1000 900
Intensity (a. u.)
800 700 600 500
400 300 200 100 0 350
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 4-14: Fluorescence emission spectra of 3 wt% Ho3+ doped TiO2 gel under 450 nm excitation at room temperature.
1000 900 Intensity (a. u.)
800 700 600 500 400 300 200 100 0 350
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 4-15: Fluorescence emission spectra of 5 wt% Ho3+ doped TiO2 gel under 450 nm excitation at room temperature.
)96)
Chapter Four
Results and Discussion
1000 900
Intensity (a. u.)
800 700 600 500 400
300 200 100 0 350
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 4-16: Fluorescence emission spectra of 7 wt% Ho3+ doped TiO2 gel under 450 nm excitation at room temperature.
From the above spectra, it is clear that; by increasing the Ho3+ concentrations, there is an obvious systematic decreasing in the intensity of these emission bands, this may be related to the location of the dopant ions in the titania host. At 5 wt% dopant concentration, the intensity of emission band is weaker than the intensity of 3 wt% dopant concentration; this could be explained as follows: At 3 wt% concentration, part of the dopant ions substitutionally were entered the structure of the TiO2 host via substituting with Ti4+ ions, the other part were entered the pores of titania host, by increasing Ho3+concentration into 5 wt% , the part of ions which were entered the titania pores had been increased, since the water, residual organics of alcohol, and some unhydrolyzed species were located inside these pores, they might have a significant role in decreasing the intensity of emission transition that was occured between the energy level of the dopant ions. Finally, when the amount of the dopant ions reached 7 wt%, a notable decrease in the intensity of its emission peak could be observed comparing with 3 wt% dopant concentration, this might be due to appearing of clustering effect in which the average distance between the dopant ions were decreased, led to aggregation )96)
Chapter Four
Results and Discussion
of these ions together, so the number of emitting centers were decreased, and caused decreasing the intensity of emission and quenching it [88]. For the second pumping wavelength 539 nm, there was no any resulted emission, this may be because of these reasons: (i) either this pumping wavelength does not excite all Ho3+ ions into upper levels, this means that enough population inversion could not be obtained which it is a required condition for emission. (ii) Or may belong to overcoming a non-radiative decay over a radiative decay [96, 97]. (iii) Finally may due to resonance fluorescence process. The third pumping wavelength 644 nm led to obtaining different emissions as demonstrated bellow: At 1 wt% dopant concentration two emission peaks centered at (389 and 595) nm had been observed, as depicted in figure (4-17). For 3 wt% dopant concentration emission bands had been obtained peaking at (384, 489, and 603) nm, as shown in figure (4-18). While 5 wt% Ho3+ ions were emitted (380, 500, 611) nm, as appeared in figure (4-19). Finally, at 7 wt% Ho3+ concentration two peaks were centered at (373 and 491) had been observed, as depicted in figure (4-20). These results may be due to upconversion transitions which were in agreement with [83, 84, 98].
)97)
Chapter Four
Results and Discussion
1000 900 800 Intensity (a. u.)
700 600 500 400 300 200 100
0 350
400
450
500
550
600
650
700
750
800
850
900
Wavelength (nm)
Fig.4-17: Fluorescence emission spectra of 1 wt% Ho3+ doped TiO2 gel under 644 nm excitation at room temperature.
1000 900 800
Intensity (a. u.)
700 600 500 400
300 200 100 0 350
400
450
500
550
600
650
700
750
800
850
900
Wavelength (nm )
Fig.4-18: Fluorescence emission spectra of 3 wt% Ho3+ doped TiO2 gel under 644 nm excitation at room temperature.
)98)
Chapter Four
Results and Discussion
1000 900 800
Intensity (a. u.)
700
600 500 400 300 200 100 0 350
400
450
500
550
600
650
700
750
800
850
900
Wavelength (nm)
Fig.4-19: Fluorescence emission spectra of 5 wt% Ho3+ doped TiO2 gel under 644 nm excitation at room temperature.
1000 900 800 700
Intensity (a. u.)
600 500 400 300 200 100 0 350
400
450
500
550
600
650
700
750
800
850
900
Wavelength (nm)
Fig.4-20: Fluorescence emission spectra of 7 wt% Ho3+doped TiO2 gel under 644 nm excitation at room temperature.
)99)
Chapter Five
Conclusions and Future work
Chapter Five Conclusions and Future Work
5.1 Conclusions In this study, pure and Ho3+-doped titania samples had been prepared. Via different techniques the structural and optical properties of the prepared samples had been obtained. All resulted data throughout this research may become a comparison for the future studies. In this section, referring to the precedent results some notable conclusions can be drawn: 1. Apperance of the prepared alkoxide solution and samples: Pure and Ho3+ doped TiO2 sol containing HCl as a catalyst and low water content remain clear and transparent during and after hydrolysis and polycondensation reactions. The viscosity of these sols increases with time before gelling, then solidified into bulk elastic gels, and finally broken into numerous small particles on expose to air. Keeping pure and Ho3+ doped TiO2 sol inside the closed tube without exposing it to air, leads to obtain the transparent rod. 2. X-ray diffraction analysis exhibit several results, including: The prepared pure and doped TiO2 nanopowder has anatase phase after calcined at 500 C for 1h, without appearing any rutile phase. This is confirmed by the presence of these diffraction peaks (101), (004), (200), (105), (211), (204), (116), (220), and (215), which is related to the anatase phase.
(87)
Chapter Five
Conclusions and Future work
The anatase lattice is shown to deform predominantly along the c-axis due to substitutionally-incorporated Ho3+ ions. The random change in the grain size of the doped titania is obtained comparing with the pure titania, due to locating the Ho 3+ ions in different locations of titania host such as: on its surface, inside its pores, while part of the dopant ions enter the TiO2 lattice by replacing substitutionally with its Ti4+ ions. 3. From FTIR spectra, these results are obtained: The chemical structure of the titania nanopowder are studied using FTIR technique, the obtained spectra shows several vibration modes of TiO 2 such as Ti-O and Ti-O-Ti in the finger print region, the existence of these bonds in the titania network is indicating that the cross-linkage between titania particles are well formed; this indicate the fact that the condensation reaction successfully completed. The infrared spectra of the doped samples show the presence of some organic groups after calcination, this is due to the existence of the dopant which inhibits complete releasing of these organics during calcination step. 4. From optical and spectroscopic characterization, these results are obtained: Pure TiO2 sample is not absorbed in the visible region. For (3, 5, and 7) wt% Ho3+ doped samples have three absorption bands which are observed at (450, 539, 644) nm due to (5I8→5F1,5G6), (5I8→5F4,5S2) and (5I8→5F5) transitions respectively, while 1 wt% Ho3+ doped sample has only one absorption peak at 644 nm, without any absorption peak at both (450 and 539) nm. This shows that, these pumping wavelengths may not excite this small amount of the Ho3+ ions well for achieving population inversion, therefore; it does not have any emission. (87)
Chapter Five
Conclusions and Future work
Upon 450 nm excitation, all the doped samples have emission in the visible wavelength region due to (5F4, 5S2→5I8), and (5F3→5I8) transitions, except for 1 wt% doped samples (as mentioned above). There is not emission for 539 nm pumping wavelength, this belongs to : either this pumping wavelength does not excite all Ho3+ ions into upper levels, so population inversion could not be achieved which it is a required condition for emission, or due to overcoming a non- radiative decay over a radiative decay, or because of resonance fluorescence process. Under 644 nm, different emissions has been observed in both UV/Vis region which may due to upconversion transitions. The resulted emission spectra of the doped samples suggest that Ho 3+doped TiO2 host prepared via sol-gel method is a good candidate for selecting as a laser active medium.
5.2 Future work Using Judd-Ofelt theory for obtaining emission intensity parameters between the energy levels of Ho3+ ions after excitation process. Study the effect of calcination temperatures above (500C) on the anatase to rutile phases transformation for pure and of Ho3+ doped TiO2 gel. Study the effect of variation of these parameters that affect on the path of sol-gel reaction such as pH, water molar ratio, alkoxide molar ratio, and the solvents, which in turn affect the structure of a final product and its luminescence property. Study the mechanical properties of pure and Ho3+ doped TiO2 samples.
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Chapter Five
Conclusions and Future work
Using more analysis techniques for analyzing samples such as: Atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman technique. Study the effect of higher dopant concentration on the emission process. Study the non-linear optical properties of Ho3+ doped TiO2 samples by Z-Scan system.
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المستخلص ذى فٗ ْزا انثحس ,إعرعًال غشٚمح (عٕل-جم) نرحعٛش عُٛاخ شُائٗ أٔكغٛذ ذٛرإَٛو ()TiO2 انُمٛح ٔانًشٕتح ترشاكٛض يخرهفح (1, 3, 5, 7 (wt%أل ٌٕٚانٕٓنٕيٕٛو انصالشٗ Ho3+كًادج صهثح نٛضسٚح ٔتأفعم ذشكٛض يٕالسٖ ( )1: 1: 10: 0.1نهًٕاد األٔنٛح ] .[TTIP: H2O: EtOH: HClذى ذحهٛم انعُٛاخ انًحعشج تإعرعًال ذمُٛاخ يخرهفح ذعًُد ذمُٛح حٕٛد األشعح انغُٛٛح (,)XRD يطٛافٛح األشعح ذحد انحًشاء ( ,(FTIRيطٛافٛح األيرصاص (,(UV/Vis Spectrophotometer ٔ يطٛافٛح انفهٕسج (.(Spectrofluorophotometer اظٓشخ َرائج ذمُٛح حٕٛد األشعح انغُٛٛح ( )XRDنًغاحٛك TiO2انُإَٚح انرشكٛة انُمٛح ٔانًشٕتح تأ Ho3+ ٌٕٚتأَٓا ذًرهك انرشكٛة انًرعذد انرثهٕس نًادج ٔ TiO2تطٕس األَاذٛظ عُذ حشلٓا تذسجح ( )500oCنًذج عاعح ٔاحذج ,ذًصهد تمًى االَعكاط (,(211( ,(105( ,(200) ,(004( ,)101 ( .(215( ٔ ,(220( ,(116( ,(204تُٛد انُرائج اٚعا ً عذو ٔجٕد لًى اَعكاط ذُغة انٗ أHo3+ٌٕٚ داخم انرشكٛة انثهٕس٘ نهعُٛاخ انًشٕتح ,لذ ُٚعضٖ انغثة ف ٙرنك انٗ ذشكٛض أ ٌٕٚانًعاف انز٘ ٚكٌٕ ألم يٍ حذٔد انكشف نجٓاص ( )XRDانًغرعًم .ذى حغاب شٕاتد انشثٛكح انشتاعٛح نطٕس االَاذٛظ انًرًصهح تانًعهًاخ ' ،'c' ٔ 'aنصُائ ٙأكغٛذ انرٛرإَٛو )ٔ (TiO2تاعرعًال يٕلع لًر (2) ٙاالَعكاط ) ،(200) ٔ (101فٕجذ شثٕخ لًٛح ' ٔ 'aذغٛشاً عشٕائٛا ً نمًٛح ' 'cتضٚادج َغة انرشٕٚةٔ .لذ أُعض٘ رنك انٗ اعرثذال تعط يٕالع إَٔٚاخ انرٛرإَٛو انشتاعٛح Ti4+تإَٔٚاخ انٕٓنٕيٕٛو انصالشٛح Ho3+داخم انرشكٛة انثهٕس٘ نهـ .TiO2ذى ذحذٚذ عشض يُرصف شذج لًح االَعكاط ) (FWHMنطٕس االَاذٛظ ( )101انر ٙاعرُعً ْ هد نحغاب انحجى انحثٛث ٙنهرشكٛة انثهٕس٘ نًغاحٛك TiO2انُمٛح ٔانًشٕتح, فاظٓشخ ذغٛشاً عشٕائٛا ً ف ٙلٛى انحجى انحثٛث ٙتضٚادج َغة انرشٕٚة ٔ أُعزي رنهك انٗ َفظ انغثة اعالِ. ْ عرعًهد يطٛافٛح األشعح ذحد انحًشاء ( (FTIRنًعشفح ذشكٛة انعُٛاخ انًحعشج ٔاظٓشخ أ األغٛاف انُاذجح ٔجٕد أاصش انرٛراَٛا ( )Ti-O) ٔ (Ti-O-Tiف ٙعُٛاخ TiO2انُمٛح ٔانًشٕتح .كًا اظٓشخ اغٛاف انعُٛاخ انًشٕتح ٔجٕد حضيح ايرصاص عُذ انعذد انًٕج(1338, 1339) cm-1 ٙ ذُرً ٙانٗ أٔ HO3+ ٌٕٚنهرشاكٛض ,(3, 5, 7( wt%تًُٛا ال ذٕجذ حضيح ايرصاص يهحٕظح عُذ انرشكٛض 1 wt%نأل Ho3+ ٌٕٚانر ٙذكٌٕ غٛش كاف ّٛنحذٔد انكشف نجٓاص .FTIR ُأجريت يحأالخ ذجشٚثٛح عذٚذج نمٛاط غٛف اإلَثعاز (انفهٕسج) نهعُٛاخ انًحعشجٔ ,اظٓشخ َرائج أغٛاف األيرصاص ٔاَثعاز انفهٕسج انًغجهح عذو ٔجٕد أ٘ لًح ف ٙغٛف األيرصاص نعُٛح
TiO2انُمٛح ظًٍ انًذٖ )400-800( nmيًا ٚذل عهٗ آَا ال ذًرهك أ٘ ايرصاص ظًٍ انًذٖ انًشئ .ٙتًُٛا اظٓشخ انُرائج ٔجٕد حضو ايرصاص يهحٕظح عُذ )450, 539, 644 ( nmنهعُٛاخ انًشٕتح تأ Ho3+ٌٕٚنهرشاكٛض ٔ (3,5,7( wt%انر ٙذعضٖ انٗ األَرماالخ ),(5I8→5F5 )) 5I8→5F1,5G6(,(5I8→5S2,5F4عهٗ انررانٔ ,ٙعذو ٔجٕد حضو ايرصاص عُذ (450, 539) nm نهرشكٛض )ُ ٔ ،(1 wt%أعزي رنك انٗ ذشكٛض إَٔٚاخ Ho3+انمهٛم غٛش انكاف ٙنرٓٛٛجٓا عُذ انطٕنٍٛ انًٕج ٍٛٛاعالِ. اظٓشخ انُرائج اَثعاز انفهٕسج انًغجهح ٔجٕد اغٛاف يخرهفح نطٕل انرٓٛج 450 nmنهعُٛاخ انًشٕتح ذمع ظًٍ انًذٖ انًشئٔ ٙانر ٙذماتم األَرماالخ ) ,(5F4, 5S2→5I8), (5F3→5I8تًُٛا نى ُٚعط ٙغٕل ذٓٛج 539 nmأ٘ غٛف اَثعاز ٔ لذ أعض٘ عثة ف ٙرنك انٗ عًهٛح انفهٕسج انشَُٛٛح. أيا عُذ غٕل انرٓٛج ,644 nmظٓشخ لًى اَثعاز يخرهفح ظًٍ انًذٖ انًشئٔ ٙفٕق انثُفغج ٙانرٙ لذ ذعضٖ انٗ اَثعاز يحٕنّ انٗ اعهٗ (. (Upconversionإذعح يٍ فحٕصاخ إَثعاز انفهٕسج إيكاَٛح ذحعٛش عُٛاخ ُ TiO2يشٕتح تأ Ho3+ ٌٕٚكٕعػ نٛضسٖ فعال.
تحضٌر و تحلٌل الوسط اللٌزري الفعال Ho3+:TiO2 باستعمال تقنٌة سول -جل
رسالة مقدمة الى مجلس كلٌة التربٌة فً جامعة السلٌمانٌة كجزء من متطلبات نٌل شهادة ماجستٌر فً علوم الفٌزٌاء ( لٌزر)
من قبل
طةشاو كنال عارف بكالورٌوس فى الفٌزٌاء ( ,)2011جامعة السلٌمانٌة باشراف
د.ماجدة علي امني الزنطنة أستاذ مساعد
طوالَن
ايار
2717
2017
ثوختة
لةم تويَريهةوةيةدا زِيَطةى (ضوَلَ-جيَلَ) بةكارهيَهزا بوَ ئامادةكسدنى دوانوَكضيدى تيتانيوَم )(TiO2ى بىَ خةوش و خمَتةداز بة ئايونةكانى هاوهيَشى صيانى هوَلَميوَم ) (Ho3+وةكو مادةى زِةقى لةيصةزى لةطةلَ خةضتى جياواشى (1, 3, 5, and 7) wt%ى ئايوَنةكانى ) (Ho3+و باشرتيو زِيَرةى موَالزى ) (1: 1: 10: 0.1بوَيةزيةكة لة ) (TTIP: H2O: EtOH: HClكة مادةى صةرةتايني. كوَمةَليَك تةكهيكى جياواس بةكارهيَهزا بوَ شيتةلَكارى منوونة ئامادةكساوةكاى وةكو:
الدانى تيشكة ئيَكضى ) ,(XRDثيَوانى شةبةنطى تيشكى ذيَس ضووز ) ,(FTIRشةبةنط ثيَوى يةلَنريو لةناوضةى ضةزوو بهةوشةيى و زِووناكى بيهزاودا ( (UV/Vis spectrophotometer شةبةنط ثيَوى دةزضووى ).(Spectrofluorophotometer ئةجنامةكانى تةكهيكى الدانى تيشكة ئيَكضى ) (XRDيازِاوةى ( )TiO2ى ب َى خةوش و خمَتةداز بة ئايوَنةكانى(( (Ho3+دواى طةزم كسدنياى لة ثمةى طةزمى بةزشى 500 Cبوَ ماوةى كاتذميَزيَك) ئةوة دةزدةخات كة ثيَكهاتةى كسيطتالَى (ئةنةتيَط) ياى يةية نويَهساوة بة لوتكةكانى الداى ( .(215( ,(220( ,(116( ,(204( ,(211( ,(105( ,(200) ,(004( ,)101ييض لوتكةيةك دةزنةكةوتوة كة تايبةت بيَت بة ئايوَنةكانى ( (Ho3+لةناو ثيَكهاتةى منوونة خمَتةدازةكاى ,يوَكازى ئةمةش دةطةزِيَتةوة بوَكةمى خةضتى خمَتة تيَكزاوةكة كة كةمرتة لة مةوداى هةصتبيَكزدنى ئاميَزى ) (XRDى بةكازياتوو .نةط َوزِةكانى ثيَكهاتةى توَزِةكى زِةوطةى (ئةنةتيَط) ( )TiO2ى دوَشزاوةتةوة بة بةكازييَهانى شويَهى لوتكةكانى ) (2ى ) (101و ) (200ى زِةوطةى ئةنةتيَط كةنويَهساوة بة ' 'aو ' .'cئةجنامةكاى ئاماذة دةكةى ب َو جيَطريى نسخى ' 'aو طوَزِانى يةزِةمةكى نسخى ' 'cبةشياد بونى خةضتى خمَتةكة .يوَى ئةمةش دةطةزِيَتةوة بوَ جيَطزتهةوةى شويَهى يةندىَ لة ئايوَنةكانى هاوهيَشى ضوازى تيتانيوَم ( (Ti4+بة ئايوَنةكانى هاوهيَشى صيانى هوَلَميوَم ( (Ho3+لة ثيَكهاتةى كسيطتالَى ( )TiO2دا .بة ثشت بةضنت بة ثانى تةواو لة شوَزتسيو نيوةدا ) (FWHMبوَ لوتكةى ( )101ى زِةوطةى ئةنةتيَط قةبازةى كسيطتالَى
يازِاوةى ( )TiO2بىَ خةوش و خمَتةداز دوَشزاوةتةوة ,طوَزِانى يةزِةمةكى لة نزخةكانيدا دةزكةوتووة بةشياد بونى خةضتى خمَتةكة كة ئةطةزِيَتةوة بوَ يةماى ئةو يوَكازةى لةضةزةوة باضكسا.
تةكهيكى ثيَوانى شةبةنطى تيشكى ذيَس ضووز ) (FTIRبةكازييَهسا بوَ سانيهى ثيَكهاتةى منوونة ئامادةكساوةكاى ,شةبةنطة بةدةضتًاتووةكاى بوونى بةندةكانى تيتانيا ) (Ti-O-Tiو ) ) Ti-Oدةزدةخةى لة منوونة بىَ خةوش و خمَتةدازةكانى ( )TiO2دا .يةزوةيا شةبةنطى منوونة خمَتةدازةكاى بوونى ضةند طوزشةيةك لةدةوزى ذمازة شةثوَىل )(1338, 1339
cm-1دةزدةخةى كة دةطةزِيَتةوة بوَ ئايوَنةكانى ( )Ho3+لة خةضتى (3, 5, 7( wt%دا. لةكاتيَكدا ييض طوزشةيةك بةدى نةكسا لة خةضتى 1 wt%ئايوَنةكانى ( , )Ho3+كة ئةم بسِة لةمةوداى هةصتثيَكزدنى ئاميَسى ( (FTIRدا نى ية. كوَمةلَيَك يةولَى كسدازى ئةجنام دزا بوَ ثيَوانى شةبةنطى بسيطكانةوةى منوونة ئامادةكساوةكاى .ئةجنامةكانى شةبةنطى يةلَنريهى منوونةى ( )TiO2بىَ خةوش ئةوة دةزدةخات كة هيض لوتكةيةكى نى ية لة مةوداى شةبةنطى .)400-800( nmئةمةش ئاماذةية بوَ ئةوةى كة ( )TiO2بىَ خةوش تواناى يةلَنريهى نى ية لة ناوضةى زِووناكى بيهزاودا .لةكاتيَكدا ضىَ طوزشةى يةلَنريو بةدى كسا لة شةبةنطى منوونة خمَتةدازةكاى بةتةواوى لة )450, 539, 644 ( nmدا بوَ خةضتى (3, 5, 7( wt%ى ئايوَنةكانى ( )Ho3+كة بةزامبةزة بة طواضتهةوةكانى),(5I8→5F5 ) .(5I8→5F1,5G6( ,(5I8→5S2,5F4لة خةضتى 1 wt%ى خمَتةكةدا هيض طوزشةيةكى يةلَنريو نى ية لة (450, 539) nmيوَى ئةمةش دةطةزِيَتةوة بوَ نةووزوذاندنى ئةو بسِة كةمةى ئايوَنةكانى ( )Ho3+بةزةو ئاضتةكانى ضةزووتس .لةكاتى ووشةثيَداى بة منوونة خمَتةدازةكاى بة دزيَرة شةثوَىل 450 nmكوَمةلَيك شةبةنطى جياواشى بسيطكانةوةى دةزضووى لة لة ناوضةى زِووناكى بيهزاودا بةدى كسا كة بةزامبةزة بوَ طواضتهةوةكانى ).(5F4, 5S2→5I8), (5F3→5I8 لة كاتيَكدا بوَ ووشة ثيَدانى 539 nmييض جوَزة شةبةنطيَكى دةزضووى بةدى نةكسا بةيوَى زِوودانى كسدازى شزنطانةوةى بسيطكانةوة .لةكاتى ووشة ثيَدانى 644 nmضةند لوتكةيةكى جياواش بةدى كسا لة ناوضةى ضةزو بهةوشةيى و زِووناكى بيهزاودا كة لةوانةية بةيؤى كسدازى ( )upconversionثةيدابووبيَت .ئةجنامةكانى شةبةنطى بسيطكانةوةى دةزضوونى منوونةى ( )TiO2ى خمَتةداز بة ئايوَنةكانى ( )Ho3+ئاماذةيةكى طوجناو و لةباز دةدةى بة ئازِاضتةى ئامادةكسدنى ناوةندى ضاالكى لةيصةز.
ئاوادةكردن و شيتةلَكارى ناوةندى ضاالكى لةيسةر Ho3+:TiO2 بة بةكارهيَنانى تةكنيكى شوَهَ-جيَنَ ناوةيةكة ثيَصكةش كراوة بة ئةجنووةنى كؤليَجى ثةروةردة لة زانكؤى شميَىانى وةك بةشيَك لة ثيَداويصتيةكانى بةدةشتويَنانى برِواناوةى واشتةر لة زانصتى فيسيا (لةيسةر)
لةاليةن طةشاو كىاه عارف بةكالؤريؤس لة فيسيا( ,)3122زانكؤى شميَىانى بةشةرثةرشتى د.واجدة عمي اوني زةنطةنة ثرِوَفيصوَرى ياريدةدةر
طوالَن
ئايار
2717
2017
