MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY LE THI THAO VIEN Synthesis and properties of undoped and transition metal (Mn2+, Cr3+) doped Zn2SiO4 and Zn2SnO4 phosphors DOCTORAL DISSERTATION ON MATERIAL SCIENCES HANOI – 2020 MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY LE THI THAO VIEN Synthesis and properties of undoped and transition metal (Mn2+, Cr3+) doped Zn2SiO4 and Zn2SnO4 phosphors Majors: Material Sciences Code: 9440122 DOCTORAL DISSERTATION ON MATERIAL SCIENCES ADVISORS: 1. PHAM THANH HUY 2. NGUYEN THI KHOI HANOI – 2020 COPYRIGHT DECLARATION This thesis compresses only my research results. It does not contain any previous data submitted by any people or organizations except that have been marked in the references.
Hanoi, 15/9/2020 Advisors PhD. Pham Thanh Huy Le Thi Thao Vien i ACKNOWLEDGEMENTS Although my name is on the cover of this dissertation, many people were of great importance to this research. I want to take a moment to extend my gratitude to the involved. The first, I would like to express my sincerest thanks to my supervisor, Prof.
Pham Thanh Huy, excellence and estimable teacher, for all of his supports. His dedication to science has been encouraging me so much, protected me from the confusion since I started studying and researching at the Advanced Institute for Science Technology (AIST). This dissertation was carried out at AIST, together with several research groups researches. I had garnered variable information from these seminars with free discussions coming from all of our group members.
Possibly just as important as the practical aid was the friendly, cooperative atmosphere at AIST; it made me enjoy virtually every second of working on my dissertation. I wish to thank Associate prof. Dao Xuan Viet; Dr. Nguyen Tu; Dr.
Nguyen Duy Hung, and all of my teammates for their friendships with kind-hearts and unconditional assistance. The last few months weren’t easy, and I want to thank all my dearest friends, who helped me get back on track when I lost my laptop and found many difficulties in life. Without your care, understanding, and motivational speeches, this thesis would no doubt look different and not for the better. Your friendship makes me realize what a lucky person I am.
For the last, more than I can say, I would like to express manifest thanks to my husband and two children for always being by my side, putting their truth in me during my duration at AIST. Lastly, I want to mention my father, mother, my parents-in-law, and two sisters, and thank them for making me the person that I have become. Le Thi Thao Vien ii CONTENTS LIST OF FIGURES. viii LIST OF TABLES.
xiv BRIEF INTRODUCTION. Background of Luminescence. Background of Transition Metal (TM) ions in the crystal field………10 1. The effect of crystal fields on the separation of TM ions…………… 11 1.
Tanabe-Sugano diagrams. Energy levels of Mn2+ ion in a crystal field. Energy levels of Cr3+ ion in a crystal field. Literature review of transition metal (Mn 2+, Cr3+) doped Zn2 SiO4 and Zn2 SnO4 phosphors.
Structure and optical properties of Zn2SiO4: Mn2+…………………. Structure and optical properties of Zn2SnO4, Zn2SnO4:Mn2+ ………………………………………………………………………………………………………………………… 24 1. Phosphor-based LEDs. Phosphor-based LEDs.
LED application in agricultural lighting. Synthesis of Zn 2SiO4, Zn2 SiO4:Mn2+, Zn2 SnO4, Zn2 SnO4 :Mn2+, Zn2 SnO4 :Cr3+, Zn2 SnO4:Cr3+, Al3+. Synthesis of Zn2SiO4. Synthesis of Zn2SiO4: Mn2+.
Synthesis of Zn2SnO4. Synthesis of Zn2SnO4:Mn2+. Synthesis of Zn2SnO4:Cr3+ and Zn2SnO4:Cr3+, Al3+. LED package process.
STRUCTURE AND OPTICAL PROPERTIES OF Zn2SiO4 AND Zn2SiO4:Mn2+ PHOSPHORS. Structure and optical properties of Zn2 SiO4 phosphors. X-ray diffraction of Zn2SiO4. Phosphor morphology of Zn2SiO4.
Vibrational analysis: Raman spectra of Zn2SiO4. Structure and optical properties of Zn 2 SiO4 :Mn2+ phosphors. X-ray diffraction of Zn2SiO4:Mn2+. Phosphor morphology of Zn2SiO4:Mn2+.
Vibrational analysis of Zn2SiO4:Mn2+. Optical properties of Zn2SiO4:Mn2+. Thermoluminescence (TL) properties and Decay time of Mn2+ doped Zn2SiO4. Application of Mn2+ doped Zn2SiO4 on UV LED.
STRUCTURE AND OPTICAL PROPERTIES OF Zn2SnO4 AND Zn2SnO4:Mn2+ PHOSPHORS. Structural and optical properties of Zn 2 SnO4 phosphors. X-ray diffraction of Zn2SnO4. Optical properties of Zn2SnO4.
Structural and optical properties of Zn 2 SnO4:Mn2+. X-ray diffraction of Zn2SnO4:Mn2+. Phosphor morphology of Zn2SnO4:Mn2+. Optical properties of Zn2SnO4:Mn2+.
Decay time of 5%Mn2+ doped Zn2SnO4. Temperature-dependent PL and internal quantum efficiency of Zn2SnO4:5%Mn2+ phosphors. Application of un-doped and Mn2+ doped Zn2SnO4 on LED. OPTICAL PROPERTIES OF Zn2SnO4:Cr3+ AND Zn2SnO4:Cr3+, Al3+ FOR PLANT CULTIVATION LED.
Structural and optical properties of Zn 2 SnO4:Cr3+ phosphors. X-ray diffraction of Zn2SnO4:Cr3+. Phosphor morphology of Zn2SnO4:Cr3+. Optical properties of Zn2SnO4:Cr3+.
Application of the prepared phosphor for fabricating infrared LEDs. Structural and optical properties of Zn 2 SnO4:Cr3+, Al3+ phosphors 106 5. X-ray diffraction and FESEM of Zn2SnO4:Cr3+,Al3+. Crystal field analysis.
The effect of Al3+ on optical properties of ZTO: Cr3+. Application of the prepared phosphor. 117 CONCLUSIONS AND FUTURE WORKS. 125 v LIST OF ACRONYMS Acronyms Full name EDX/EDS: Energy-Dispersive X-ray spectroscopy LED: Light Emitting Diode NIR: Near-infrared PL: Photoluminescence SEM: Scanning Electron Microscope XRD: X-Ray Diffraction FESEM: Field emission scanning electron Microscope PLE: Photoluminescence excitation UV: Ultraviolet HWHM: Half-Width at half-maximum IR: Infra-red TM: Transition Metal EL: Electroluminescence NBOH: Non – bridging oxygen hole centers RGB: Red, Green and Blue FTIR: Fourier – transform infrared spectroscopy HEBM: High – energy planetary ball mill AIST: Advanced Institute for Science and Technology JCPDS: Joint committee on powder diffraction standards FWHM: Full width at half maximum vi Zni: Zinc interstitials Sni: Tin interstitials Oi : Oxygen interstitials Vo : Oxygen vacancy WBG: Wide band gap ZTO: Zinc stannate VZn: Zinc vacancy VSn: Tin vacancy TG-DTA: Thermogravimetry/Different thermal analyzer CRI: Color rendering index CCT: Correlated color temperature BM: Brurstein – Moss WLED White light-emitting diode QE Quantum efficiency AO Atomic orbitals vii LIST OF FIGURES No.
Name Page Shapes of d orbitals and ligand positions ○: Ligands for Figure 1.1 11 octahedral symmetry: Ligands for tetrahedral symmetry The separation of AO d of the transition metal ions in Figure 1.2 12 octagonal symmetry The separation of AO d of the central ion by the crystal Figure 1.3 13 field in different symmetry The separation of energy levels of some transition metal ions due to electrostatic interaction (a) and the energy Figure 1.4 14 level separation of Cr 3+ ions when take into account the spin-orbit interaction L-S (with B = 918 cm -1 ) (b) Figure 1.5 3d level splitting caused by the crystal field 15 Energy level diagram for the d 2 configuration., Ligand Field Figure 1.6 16 Theory and its Applications, Syokabo, Tokyo, 1969 (in Japanese) Energy level diagram for the d3 configuration., Ligand Field Figure 1.7 17 Theory and its Applications, Syokabo, Tokyo, 1969 (in Japanese) Energy level diagram for the d5 configuration., Ligand Field Figure 1.8 17 Theory and its Applications, Syokabo, Tokyo, 1969 (in Japanese) Tanabe–Sugano diagram for the Mn 2+ in Zn 2SiO4 crystal Figure 1.9 19 field Tanabe–Sugano diagram for the Cr 3+ electron Figure 1.10 21 configuration in the octahedral crystal field.7 (a) The number of SiO 4− units that are connected together Figure 1.11 by sharing the oxygen atoms and (b) Structure of the 23 Willemite -Zn2 SiO4 Figure 1.12 Structural models for the cubic spinel -Zn2 SnO4 25 General approaches for achieving white LEDs.13 27 Single-emitting-layer structure. (B) Multi emitting layer viii structure. (E) Down-conversion white LEDs. Three principal white-lighting strategies.14 A three-phosphor strategy with a UV LED and RGB 27 phosphors.
(c) A blue LED with a yellow down- converting phosphor Figure 2.1 Synthesis Zn 2SiO4 powder process 33 Ball-powder – ball collision of powder mixture during Figure 2.2 35 mechanical milling Figure 2.3 Scattering and diffraction. The Bragg’s law 36 FESEM instrument and schematic of a scanning electron Figure 2.5 Raman scattering 38 Figure 2.6 Principle of Fourier-transform spectroscopy 39 The basic design of an instrument for measuring Figure 2.7 40 fluorescence The basic design of an instrument for measuring UV-vis Figure 2.9 The typical of LED package structure 43 The typical of LED package structure (a) and lens- Figure 2.10 44 containing type LED package (b) Figure 2.11 The process of LED package 44 Figure 2.12 The process of die bonding 45 Figure 2.13 The process of Wire bonding 45 Figure 2.14 The process of phosphor -silicon coating 46 Figure 2.15 The process of dispensing 46 Figure 2.16 The process of curing 47 Figure 2.17 The process of testing 47 XRD patterns of ZnO-SiO2 powder with the weight ratio Figure 3.1 50 of 1:2 after high-energy planetary ball milling for 40 hours ix and annealing at different temperatures for 2 hours in air environment. FESEM and EDS images of Zn 2 SiO4 powder with the weight ratio of 1:2 after high-energy planetary ball milling Figure 3.2 for 40 hours (a) and annealing at 500 C (b); 900 C (c); 51 1000 C (d); 1150 C (e); 1250 C (f), 1300 C (g) and 1350 C (h) oC for 2 hours in air environnent Raman spectra of Zn 2SiO4 powder (with the weight ratio of 1:2) after high-energy planetary ball milling for 40 Figure 3.3 hours (a) and Zn 2 SiO4 samples after milling and annealing 52 at 900 C (b), 1250 C (c), and 1350 C (d) for 2 hours in air environment. PL spectra of Zn 2 SiO4 and after annealing at different Figure 3.4 temperatures for 2 hours in air environment (a) and 53 Gaussian Fitted of PL spectrum (b) Diagram of PL mechanism for explanation of PL emission Figure 3.5 54 of Zn2 SiO4 PL spectra of Zn 2 SiO4 with different ratio of ZnO:SiO 2 at Figure 3.5:2 (a); (1:2 (b); (2:1(c) and (2:2(d)) calcinated at 1250 54 C XRD patterns of 5 %wt Mn 2+-doped Zn2 SiO4 powders after ball-milling for 40 hours without and with annealing Figure 3.7 55 at different temperatures in the range of 500 – 1350 C in air XRD patterns of Zn 2SiO4 :x%Mn2+ (x=0-8) samples after Figure 3.8 57 milling followed by the annealing in air at 1250 C.
FESEM images of 5 wt % Mn 2+ doped ZnO/SiO 2 powders after milling for 40 hours (a), the milled sample and annealed at different temperatures for 2 hours in air: 500 Figure 3.9 58 °C (b), 900 °C (c), 1150 °C (d), 1200 °C (e), 1250 °C (f) , 1300 °C (g) and 1350 °C (h) and (i) EDS spectra of sample annealed at 1250 °C FTIR spectra of 5 wt% Mn 2+ doped ZnO/SiO 2 powders after milling for 40 hours (a), the sample after ball-milling Figure 3.10 followed by the annealing at different temperatures for 2 59 hours in air: 500 °C (b), 900 °C (c), 1150 °C (d), 1200 °C (e), 1250 °C (f) , and 1300 °C (g) x Raman spectra of 5 wt% Mn 2+-doped ZnO/SiO 2 powders after milling for 40 hours (a), the samples milled for 40 Figure 3.11 hours followed by annealing at different temperatures of 60 500 °C (b), 900 °C (c), 1150 °C (d), 1200 °C (e), 1250 °C (f) , 1300 °C (g), for 2 hours in air (a) PLE spectra measured at maxima of the emission at 740 nm (curve 1) and 525 nm (curve 2); and (b) Figure 3.12 62 photoluminescence spectrum of Zn2SiO4 sample after milling without doping and doped with 5% Mn PL spectra of 5 %wt Mn 2+ doped ZnO/SiO2 powders after Figure 3.13 milling for 40 hours followed by the annealing at different 62 temperatures in the range of 500-1350 C PL spectra of Zn 2 SiO 4:x%Mn2+ (x=0-8) samples after milling followed by the annealing in air at 1250 C.