奈米螢光體之低溫合成與光學特性研究

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(1)摘要在本研究中，主要在探討氧化鋅、鋁酸鋅和鹵磷酸鹽的奈米螢光體化學反應合成與物性及光學性質。首先對在氧化鋅生成反應，發現在ZnO/Si基板上，在 75 oC時，可合成沿c軸方向高密度的氧化鋅奈米棒。且使用氮氣氛去作熱處理，可以提升氧化鋅奈米棒在紫外光的強度。經由EXAFS量測之後，發現到氣氛可能只是被吸附或者是陷入在氧化鋅奈米棒的表面。而在奈米級鋁酸鋅粉體的生成，發現到pH值和反應的溫度，在合成奈米尺寸鋁酸鋅上扮演一個很重要的角色。在pH=7，150oC時，可以透過中間產物 (ZnAl-LDH)的生成，進而合成平均顆粒大小在 5 nm 範圍的鋁酸鋅奈米體。當奈米體表面經過表面活性劑CTAB處理之後，則可以形成ZnAl2O4/Eu核殼結構。進一步探討合成奈米級的銪摻雜鹵磷酸鹽。發現在室溫下pH=2 時，可以同時生成含有Cl和OH兩種不同的鹵磷酸鹽相。但是當pH值超過 7 時，只有含有OH 的鹵磷酸鹽相會被生成。當在經過 850oC還原氣氛熱處理之後，在不同pH值下，粉體會成呈現不同的藍色和紅色放射光強度。這些結果暗示了，紅光和藍光兩者之間相對的放射強度，可以藉由控制pH值(結晶相)和改變熱處理的氣氛來調控。. i.

(2) ABSTRACT. In this thesis, most of my researches were primarily focused on the synthesis and optical characterization of ZnO-based nanosized phosphors. Firstly, as the ZnO films were pre-treated with nitrogen implantation in the range from 5x1012 to 5x1015 ions/cm2, it was found that the peak intensity of near band-edge emission remarkably decreases with the increase of concentration of implanted nitrogen when annealed in nitrogen atmosphere. However, as the ZnO was implanted with 5x1012 ions/cm2 and annealed in oxygen atmosphere, the optical properties are improved probably. Subsequently, high-density ZnO nanorods can be vertically grown on Si coated with ZnO film (ZnO/Si substrate) from aqueous solution at 75oC. It was observed that enhancement of PL properties due to N2-atmosphere annealing for ultraviolet emission was obtained and can be attributed to the reduction of defect density. The extended x-ray absorption fine structure (EXAFS) reveals that most ions are possibly trapped or adsorbed on the surface of the ZnO nanorods and thus, the annealing atmosphere shows no apparent influence on the deep-level defects of ZnO nanorods. In addition, europium doped nanocrystalline zinc aluminate (ZnAl2O4) particles were prepared by hydrolyzing a mixture of aluminum chloride hexahydrate and zinc chloride in deionized water. At pH=7 and T>120oC, the nanocrystalline ZnAl2O4 particles with average particle size of ~5 nm are easily synthesized through ZnAl layered double hydroxide (ZnAl-LDH). After surface treatment with the cationic surfactant CTAB, the ZnAl2O4/Eu core-shell structure may be developed. The ZnAl2O4/Eu core-shell structure can show both emissions from 5D0 to 7F2 sensitivity energy level and 5D2 to 7F0 depth energy level. Finally, the synthesis and optical properties of nanocrystalline Eu-doped. ii.

(3) halo-phosphate powders, Ca5(PO4)3(OH):Eu3+, were also investigated. At pH=2, both Ca8.3Sr1.7(PO4)6Cl2 and Ca8.3Sr1.7(PO4)6(OH)2 phases were detected, but for the solution with pH value over 7, only one Ca8.3Sr1.7(PO4)6(OH)2 phase was identified. After annealed at 850oC in a reduction atmosphere, different relative ratio of blue and red emissions can be controlled through changing the various pH-solutions. These results indicate that the relative peak intensity of both red and blue emissions can be tunable by controlling the solution pH value (crystalline phase) and changing annealing atmosphere.. iii.

(4) This thesis is dedicated to my family.. iv.

(5) ACKNOWLEDGEMENT. Thanks to all people who helped me.. v.

(6) CONTENTS. ABSTRACT (IN CHINESE) ..................................................................................i ABSTRACT........................................................................................................... ii DEDICATION ...................................................................................................... iv ACKNOWLEDGEMENT ..................................................................................... v CONTENTS.......................................................................................................... vi LIST OF TABLES.................................................................................................. x LIST OF FIGURES............................................................................................... xi. CHAPTER 1 .......................................................................................................... 1 Introduction .............................................................................................................................1 1.1.. History of phosphor ..................................................................................................1. 1.2.. Principles of luminescence .......................................................................................3. 1.3.. Synthesis of nanosize phosphors ..............................................................................8. 1.4.. nanosize phosphors characterization.......................................................................13. 1.5.. Outline of this dissertation ......................................................................................15. CHAPTER 2 ........................................................................................................ 21 Experimental ........................................................................................................ 21 2.1.. Experimental process ..............................................................................................21 2.1.1. ZnO film........................................................................................................21 2.1.2. Preparation of ZnAl2O4 and Ca10-ySry(PO4)6Cl2 nano phosphors .................22. 2.2.. Characterization analysis ........................................................................................25 vi.

(7) CHAPTER 3 ........................................................................................................ 30 Physical characteristics and photoluminescence properties of nitrogenimplanted ZnO thin film ...................................................................................... 30. 3.1.. Introduction .............................................................................................................30. 3.2.. Experimental procedure ..........................................................................................32. 3.3.. Results and Discussion ...........................................................................................33 3.3.1 Physical characteristics..................................................................................33 3.3.2 Photoluminescence properties .......................................................................35. 3.4.. Conclusions.............................................................................................................40. CHAPTER 4 ........................................................................................................ 48 Physical characteristic of low-temperature grown ZnO nanorods on Si from aqueous solution and annealed at various atmospheres.............................. 48. 4.1.. Introduction .............................................................................................................48. 4.2.. Experiment procedure.............................................................................................49. 4.3.. Results and discussion ............................................................................................50 4.3.1. Microstructure and phase evolution..............................................................50 4.3.2. Spectroscopic characterization .....................................................................53. 4.4.. Conclusions.............................................................................................................55. CHAPTER 5 ........................................................................................................ 61 Effect of phase transformation on photoluminescence behavior of ZnO:Eu prepared in different solvents................................................................. 61 vii.

(8) 5.1.. Introduction .............................................................................................................61. 5.2.. Experiment procedure.............................................................................................62. 5.3.. Results and discussion ............................................................................................63 5.3.1. OH- effect......................................................................................................63 5.3.2. Eu amount.....................................................................................................65 5.3.3 Effect of excitation wavelength .....................................................................67. 5.4.. Conclusions.............................................................................................................68. CHAPTER 6 ........................................................................................................ 77 In-situ synthesis and physical characteristics of ZnAl2O4 nanocrystalline and ZnAl2O4/Eu core-shell structure via hydrothermal route ............................. 77. 6.1.. Introduction .............................................................................................................77. 6.2.. Experiment..............................................................................................................78. 6.3.. Results and discussion ............................................................................................78 6.3.1. Phase development and characterization of ZnAl2O4 ...................................78 6.3.2. Particle sized comparison of synthesized ZnAl2O4 ......................................81 6.3.3. Microstructure and photoluminescence properties of ZnAl2O4/Eu core-shell particles ..................................................................................................81. 6.4.. Conclusions.............................................................................................................82. CHAPTER 7 ........................................................................................................ 90 Physical characterization and tunable photoluminescence of Eu-doped strontium-substituted nano-halophosphate .......................................................... 90. viii.

(9) 7.1.. Introduction .............................................................................................................90. 7.2.. Experiment procedure.............................................................................................92. 7.3.. Results and discussion ............................................................................................92 7.3.1. Phase and microstructure development ........................................................92 7.3.2. Eu effect........................................................................................................94 7.3.3. Photoluminescence characterization.............................................................96. 7.4.. Conclusions.............................................................................................................98. CHAPTER 8 ...................................................................................................... 107 Conclusions........................................................................................................ 107. 8.1. Photoluminescence properties of ZnO film and nanorods under different atmosphere and annealing treatment...................................................................107. 8.2. Photoluminescence behavior of ZnO:Eu prepared in different solvents .............108. 8.3. Synthesis and optical characteristics of nanosize phosphors.................................109. REFERENCES ...................................................................................................110 PUBLICATIONS ................................................................................................119. ix.

(10) LIST OF TABLES. Table 1.1. Early milestones in the siscovery of luminescent materials and devices. ...........16. Table 1.2. Most important phosphors for practical use. .......................................................17. Table 5.1. Relative intensity ratio of 5D0→7F2 to 5D0→7F1 and 5D0→7F4 to 5D0→7F1 as a function of sintering temperature for ZnO:Eu powders................................69. Table 6.1. Average practical size of synthesized ZnAl2O4 nanopowders.............................83. x.

(11) LIST OF FIGURES. Fig. 1.1. (a) Emission spectrum of Ca5(PO4)3(Cl,F):Sb3+,Mn2+ (solid line) as used in single-phosphor lamps compared to the eye sensitivity curve. (b) Emission spectrum of BaMgAl10O17:Eu2+ (solid line), LaPO4:Ce3+,Tb3+ (dotted line), Y2O3:Eu3+ (dashed line) as used in tri-color lamps compared to the eye sensitivity curve. .....................................................................................................18. Fig. 1.2. Schemes illustrating the underlying physical processes of luminescence on (a) isolated center and (b) in semiconductors. ........................................................19. Fig. 1.3. Emission transitions in semiconductor (schematically representation). The band gap Eg separates the valence band (VB) and the conduction band (CB).........................................................................................................................20. Fig. 2.1. Flow chart for preparing ZnO nanorods. ................................................................27. Fig. 2.2. Idealized structure of a layered double hydroxide, with interlayer carbonate anions. Several parameters are defined. .................................................28. Fig. 2.3. Flow chart for preparing Ca10-ySry(PO4)6Cl2:xEu2+ nanosize phosphors. ..............29. Fig. 3.1. SIMS depth profile of various fluences of nitrogen implanted into ZnO films after annealing at 850 oC in nitrogen atmospheres. .......................................42. Fig. 3.2. XRD patterns of ZnO films with different fluences annealed in nitrogen atmospheres at 850 oC.............................................................................................43. Fig. 3.3. XRD patterns of ZnO films with different fluences annealed in oxygen atmospheres at 850 oC.............................................................................................44. Fig. 3.4. Dependence of fluences conditions on the room temperature PL Spectra of the annealed ZnO films treated at 850 oC in (a) N2 and (b) O2 atmospheres..........45. xi.

(12) Fig. 3.5. Defects’ levels in ZnO film. ...................................................................................46. Fig. 3.6. (a) Displays the O1s fitted spectra of non-implanted sample. (b) Dependence of relative intensity of the fitted components centered at O1s 531.25 ± 0.2 eV, on N-implanted fluence in different atmospheres. (a) Displays the O1s fitted spectra of non-implanted sample. .....................................47. Fig. 4.1. Morphology of annealed ZnO nanorods. (a) Not annealed ZnO nanorods, and annealed in (b) N2, (c) O2, and (d) air at 850 oC/1 h. .......................................56. Fig. 4.2. Room-temperature Raman spectrum of the ZnO nanorods annealed in (a) N2, (b) O2, and (c) air atmospheres. ........................................................................57. Fig. 4.3. PL spectra of as-grown ZnO nanorods annealed in various atmospheres at 850 oC for 1 h..........................................................................................................58. Fig. 4.4. EPR spectra of (a) as-grown and annealed ZnO nanorods in (b) N2, (c) O2, and (d) air at 850 oC/1 h..........................................................................................59. Fig. 4.5. Fourier transform of the EXAFS function at the Zn K edge for (a) as-grown and annealed ZnO nanorods annealed at 850 oC for 1 h in (b) N2 (c) O2, and (d) air atmosphere; (e) ZnO powder standard. ......................................60. Fig. 5.1. XRD patterns of the Eu2O3 powder (a) without and (b) with ball-milling in deionized water. ......................................................................................................70. Fig. 5.2. XRD patterns of 0.5 wt% Eu-doped ZnO powder mixed in (a) deionized water and (b) acetone and then sintered at 600-1000 oC/1 h. .................................71. Fig. 5.3. PL spectra of 0.5 wt% Eu-doped ZnO powder mixed in (a) deionized water and (b) acetone and sintered in air (excitation wavelength 532 nm). ...........72. Fig. 5.4. Peak shift in ZnO (1 0 1) peak as a function of Eu amount. ..................................73. Fig. 5.5. Eu mapping of the 0.5 wt% Eu-doped ZnO sample sintered at (a) 600 oC and (b) 1000 oC in air. .............................................................................................74. xii.

(13) Fig. 5.6. Temperature dependence on conductivity of Eu-doped ZnO.................................75. Fig. 5.7. PL spectra of 0.5 wt% Eu-doped ZnO powder mixed in (a) deionized water and (b) acetone in air (excitation wavelength 325nm)..................................76. Fig. 6.1.. XRD patterns of various phases by hydrothermally treating the precursors (aluminum chloride hexahydrate and zinc chloride) at 180 oC for 5 h at different pH values..................................................................................................84. Fig.6.2. XRD patterns of the solution with pH = 7 prepared by hydrothermal treatment at various temperatures for 5 h. ..............................................................85. Fig. 6.3. FTIR spectra of various phases by hydrothermally treating the precursors at various pH values................................................................................................86. Fig. 6.4. TEM image of synthesized ZnAl2O4 nanoparticles................................................87. Fig. 6.5. TEM image of Eu-coated ZnAl2O4 nanoparticles, mark =20 nm. .........................88. Fig. 6.6. PL spectra for ZnAl2O4/Eu core-shell particles excited by 390 nm. ......................89. Fig. 7.1. X-ray diffraction patterns of nano-halophosphate synthesized from the chemical solution with different pH values as room temperature. .......................100. Fig. 7.2. SEM microstructure of the halophosphate particles synthesized from the chemical solution with different pH values (a) pH = 2, (b) pH = 8, and (c) pH =10 at room temperature. ................................................................................101. Fig. 7.3. TEM image of the halophosphate particles synthesized from the chemical solution with different pH values (a) pH = 2 and (b) pH = 10 at room temperature.. .........................................................................................................102. Fig. 7.4. XRD diffraction patterns of the halophosphate powders synthesized from the chemical solution with different pH values and then annealed at 850 oC for 2 h in H2/N2 atmosphere..................................................................................103. Fig. 7.5. Effect of the doped-Eu3+ content on the relative PL intensity of the halophosphate powders doped Eu.........................................................................104 xiii.

(14) Fig. 7.6. PL spectra of the (a) as-precipitated and (b) annealed halophosphate powders at 850 oC in a reduced atmosphere for 2 h dependent on different pH solutions. .........................................................................................................105. Fig. 7.7. PL spectra of the halophosphate powders prepared from the solution with different (a) pH = 2 and (b) pH = 10 values and then annealed at 850 oC in air and H2/N2 atmospheres for 2 h. .......................................................................106. xiv.

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