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AN ABSTRACT OF THE THESIS OF Dong Li for the degree of Doctor of Philosophy in Chemistry presented on April 6, 1999. Title: Phos hor Develo ment: S nthesis Characterization and Chromatic Control Redacted for privacy Abstract approved: / Douglas A. Keszler Selected phosphors of importance for continued development of flat-panel electroluminescent displays (ELDs) and field-emission displays (FEDs) have been synthesized andstudied. By using ceramic-processingmethods,solid-solution techniques, and codopants, the luminous efficiencies and chromaticities of several phosphors have been greatly improved.On the basis of these results, a trichromatic phosphor system has been proposed for upgrading ELD performance from monochrome to full-color capabilities. The maximum emission wavelength of Y2Si05:Ce3+ has been shifted by adding Sc to form the solid solution Y2..ScSiOs (0x 5_ 0.75.) Structures in thesolid-solution series were refined by the Rietveld method. The shift of the emission bandis associated with the distribution of Sc on the two crystallographic types of Y sites and the nephelauxetic effect. Eu2+-doped Mgi.CaxS luminescent powders were prepared by flowing H2S(g) over nanoparticulate Mgi_xCax0 that was prepared by the combustion method. The resulting materials were characterized by X-ray diffraction, scanning electron microscopy, and luminescence spectroscopy.The phosphor powder is characterized by faceted grains with a median particle size near 2p.m and a high cathodoluminescent efficiency: 8.07 lm/w at 2000V. GdNb04:Bi and YNbO4:Bi phosphors have been prepared by the sol-gel method. Compared to Y2SiO5:Ce, GdNbO4:Bi has a similar luminous efficiency, while YNbO4: Bi exhibits a higher efficiency. The relatively high efficiencies of these niobates are partly associated with their long wavelength emission tails. Photoluminescence emission and excitation spectra, decay curves, and thermal quenching have been measured for SrS:Cu phosphors coactivated with different 1+ and 3+ ions. The shapes and positions of peaks in the emission spectra depend solely on the local surroundings of the Cu atoms.The luminescence mechanism is explained by considering the nature of the isolated Cu coordination environments that result from the method of charge compensation. (Zn, Ga)S:Mn solid-solution phosphors were synthesized by using high-temperature solid-state reactions.The emission colors range from yellow to deep red. Explicit chromaticcontrolcanbeachievedbyadjustingtheconcentrationofGa. Photoluminescence emission and excitation spectra are reported for measurements taken at both liquid nitrogen and room temperature.The emission has been assigned to relaxation on isolated Mn2+ centers. Phosphor Development: Synthesis, Characterization, and Chromatic Control by Dong Li A THESIS submitted to Oregon Sate University In partial fulfillment of The requirements for the Degree of Doctor of Philosophy Completed April 6, 1999 Commencement June 1999 Doctor of Philosophy thesis of Dong Li presented on April 6, 1999 APPROVED: Redacted for privacy Major rofessor, representing Chemistry Redacted for privacy er of Department of Chemistry Redacted for privacy Veanof 4r Gra School I understand that my thesis will become part of the permanent collection of Oregon State University libraries.My signature below authorizes release of my thesis to any reader upon request. Redacted for privacy ACKNOWLEDGMENTS I would like to take this opportunity to express my sincere thanks to my major professor, Dr. Douglas A. Keszler, for his guidance, assistance, and encouragement throughout my entire program. Without his expertise and direction, my Ph.D. thesis may have never been completed. I would also like to acknowledge my gratitude to my committee members, Prof. Arthur Sleight, Prof. John Loeser, Prof. Michael Lerner, and Prof. Joe Karchesy for their ongoing support of my doctoral program. Next, I would like to extend thanks and appreciation to Prof J. F. Wager, Paul Kier of ECE department for teaching me EL principle and SrS:Cu thin film deposition, to Prof.J.Tate and V. Dimitrova of physics department for (ZnGa)S:Mn thin film deposition, to Prof. W. Warren and J. Janesky of physics department for performing solid state NMR, to Dr. D. Tuenge, Dr. S. Sun, and S. Moehnke of Planar for their help and advice. I am especially grateful to my friends and colleagues,all of whom have contributed to my success and made my years at Oregon State University a fun time to remember: Dr. Jun-Ming Tu, Dr. Anthony Diaz, Dr. Ki-Seog Chang, M.S. Ken Vandenberghe, M.S. Stephen Crossno, Dr. Judith Kissick, Dr. Cho, Greg Peterson, Ben Clark, Sangmoon Park, Jennifer Stone, and Melissa Harrington for their helpful discussions and fun in the research group. Special thanks go to Ju-Zhou Tao in Prof Sleight's group and Engelene Chrysostom in Prof Nibler's group for their help on my research. I also wish to thank all the faculty and staff of Department of Chemistry for their continued assistance. I would further like to acknowledge my gratitude to the faculty and classmates in Department of Chemistry, Beijing University and my motherland China. Finally, I would like to acknowledge my deep debt of gratitude to my parents, my wife, other family members and friends for all the support and encouragement they have given me throughout my studies. TABLE OF CONTENTS CHAPTER 1: INTRODUCTION 1 Luminescence Process 3 Phosphor Characteristics in Display Function 4 FED Emission Display 9 AC Thin-Film Electroluminescence (ACTFEL) 12 This Work 16 References 18 CHAPTER 2: LUMINESCENCE OF Y2_xScxSi05:Ce3+ 19 Abstract 20 Introduction 20 Experimental 20 Results 22 Crystal Structure 22 Rietveld Refinement 26 Photoluminescence 29 Discussion 32 Conclusions 35 References 36 CHAPTER 3: Mgi_xCaxS:Eu (05.0.2) LUMINESCENCE MATERIALS FROM COMBUSTION PRECURSORS 37 Abstract 38 Introduction 38 Experimental 39 Results and Discussion 40 Characterization of Oxide 41 Characterization of Sulfide 43 Photoluminescence 50 Summary 54 Acknowledgements 54 References 54 TABLE OF CONTENTS (Continued) CHAPTER 4: NIOBATE PHOSPHORS PREPARED BY SOL-GEL METHOD 56 Abstract 57 Introduction 57 Experimental 58 Results and Discussion 60 Conclusion 67 References 68 CHAPTER 5: LUMINESCENCE OF SrS: Cu 69 Abstract 70 Introduction 70 Experimental 72 Results 72 Excitation 77 Photoluminescence decay time 81 Thermal Quenching 84 Concentration Quenching 87 Discussion 88 Excitation 90 Emission and Quenching 91 Decay Time (tentative explanation) 93 Concentration Quenching 93 Conclusion 94 References 95 CHAPTER 6: PHOTOLUMINESCENCE OF (Zn,Ga)S: Mn 97 Abstract 98 Introduction 98 Experimental 99 Results and Discussion 100 Lattice Constants 100 Photoluminescence 103 TABLE OF CONTENTS (Continued) Analysis of excitation band 112 Summary 115 References 116 CHAPTER 7: CONCLUSION 118 BIBLIOGRAPHY 119 LIST OF FIGURES Figure Page 1.1. Principal types of electronic information displays 2 1.2. Configurational coordinate diagram illustrating luminescence process 4 1.3. Luminosity curves for C.I.E. standard observer 5 1.4. Color matching functions for CIE 1931 standard observer 6 1.5. Electron emission process 10 1.6. Field emission display structure 11 1.7. Types of field emitters. 12 1.8. Standard ACTFEL structure 13 1.9. ACTFEL energy-band diagram illustrating fundamental physics 14 1.10.Energy band bending (a) without space charge, and (b) with space charge 15 2.1. Drawing of the structure of Y2SiO5. The red balls represent 05 atoms, the green and black balls represent Y1 and Y2 atoms respectively. SiO4 are designated by blue tetrahedra 23 2.2. Labeled drawing of Yl- and Y2 centered polyhedra in Y2SiO5 24 2.3 Observed (+ line) and calculated (solid line) powder diffraction pattern of Yi.25Sc0.75Si05:2%Ce. Difference curve appears at the bottom of the figure 26 2.4. Cell Volume/Z (A3) of Y2_xScSi05 28 2.5. Emission spectra of Y2SiO5:2 %Ce at 4 K and 298 K. -exck =300 nm 29 2.6. Thermal quenching of Y2SiO5:2 %Ce 30 2.7. Emission spectra of Y2,ScxSi05:2%Ce at room temperature. Xexc = 300 nm. 30 2.8. Comparison of thermal quenching of Y2SiO5:2 %Ce to Y1.75Sco.25Si05:2%Ce. Xexc 300nm, monitoring the emission peak, respectively 33 2.9. Excitation spectra of Y2,ScxSi05:2%Ce3+. Xem=450nm 34 LIST OF FIGURES (Continued) Figure Page 2.10.Excitation spectra of Y2_,,Sc,,Si05:2%Ce3+. Y2: Y2Si05, Y1.25:)(1.25SC0.75Si05, 20: Xem=520nm, 450: kem=450nm 35 3.1. X-ray powder pattern of Mg0.9Cao.10 prepared by combustion synthesis. The line is diffraction pattern of MgO... 42 3.2. Plot of the Fourier size coefficient against (a). Crystallite size distribution and (b). Median crystallite size of Mg0.9Ca43.10 43 3.3 SEM micrographs of Mg0.96Ca0.04S: 0.1%Eu2+ prepared by sulfate method (upper) and combustion method (lower) 44 3.4. Particle size distribution of Mg0.9Cao.IS determined by light scattering 45 3.5. X-ray powder diffraction pattern of Mgo.8Cao.2S:0.1%Eu 46 3.6. Lattice constants of Mgi.CaS 47 3.7, Representative Williamson-Hall plots for Mgo.9Ca0.iS: 0.1%Eu2+ 49 3.8. Emission Spectra of Mgi.xCaxS :0.1%Eu. kexe=315nm 50 3.9. Excitation spectra of Mgi.,,C aS : 0.1%Eu 51 3.10.omparison of luminous efficiency of Y203:4%Eu and Mg0.9Cao.IS:0.1%Eu prepared by combustion and sulfate/H2S method 53 4.1. Emission of YNbO4 under 254nm and 304nm excitation 60 4.2. Corrected emission and excitation spectra of YNbO4 and YNbO4:Bi 61 4.3. Emission of GdNbO4 under 254nm and 307nm excitation 62 4.4. Eexcitation and emission of GdNBo4 and GdNbO4:Bi 62 4.5. Relative brightness as a function of the bismuth concentration.. 63 4.6. Dependence of luminous efficiency on voltage 65 4.7. Schematic representation of the energy level scheme of a free s2 ion 66 5.1. Emission spectra of SrS doped samples, kexc=3 lOnm 73 LIST OF FIGURES (Continued) Figure Page 5.2.

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