氮化物螢光粉組成調控對其發光特性影響之研究

稀土元素摻雜之無機氮化物發光材料為近年來新開發出之適合白光發光二極體(LED)應用高效螢光粉，因其具有由SiN4組成之緊密共價網狀結構與較大之晶場分裂，具有比氧化物螢光粉更佳之熱穩定性與更紅位移之放光。照明用之白光LED使用氮化物螢光粉可提高演色性、熱穩定性與化學穩定性，不僅使得白光發光光譜更趨近自然光，反映真實色彩，亦延長白光LED之使用壽命。氮化物螢光粉之研製與開發促進白光發光二極體技術迅速發展。本研究以改善三種氮化物螢光粉之熱穩定性為目標，三種氮化物螢光粉分別為nitridosilicates (MSiN)、oxonitridoaluminosilicates (MSiAlON)與 nitridoaluminosilicates (MAlSiN)。應用已知物理特性作為改善熱穩定性之策略，例如： Si−C鍵之共價性高於Si−N鍵與Ba2+陽離子之熱振動頻率小於Sr2+陽離子。利用陰離子取代非活化劑格位或陽離子取代活化劑/非活化劑格位並輔以電荷補償保持電中性，調控氮化物螢光粉組成並探討其發光性質之改變。此外，對於超乎預期之發光現象，我們亦提出合理之解釋機制並輔以實驗證明。於第一部分研究中，提出鄰近陽離子控制效應來解釋此熱穩定性之變化，並從HRTEM證實Sr0.6Y1.38Si4N6.6C0.4:Ce3+0.02 中間相為兩相(SrYSi4N7 + Y2Si4N6C)共存之結構。第二部分研究中，於Sr0.92-xBaxSiAl2O3N2:Ce3+0.04,Eu2+0.04系統隨x值增加伴隨之放光光譜紅移與熱穩定性增加，乃導因於活化劑格位之化學壓壓縮效應。而第三部分研究，藉由同時摻雜Si4+與C4-離子於CaAlSiN3:Eu2+紅色氮化物螢光粉中，藉由第二配位層收縮效應之調控，熱穩定性可被大幅提升。本論文調控不同氮化物螢光粉組成，並針對發光特性提出合理之機制解釋與相對應之詳細探討與證明，相信對於解釋其他螢光粉之發光特性，有一定之參考價值。另外，對於被改善與增強之氮化物螢光粉之熱穩定性，相信於白光LED之應用具發展潛力。

關鍵字

氮化物；螢光粉；組成調控；熱穩定性；發光特性

並列摘要

Inorganic luminescent nitride doped with rare-earch elements as activators are newly developed high efficiency phosphors for white LEDs. Owing to their dense covalence frameworks constructing by SiN4 tetrahedra and larger crystal field splitting, nitride phosphors have better thermal stabilities and more red-shift emission than oxide phosphors. White LED using nitride phosphors can enhance the color rendering index, thermal stability and chemical stability. It not only cause the spectrum of white light from white LEDs to be closer to the natural light and reflect the true color of the object, but also prolong the using life of whie LEDs. The research and development of nitride phosphors promote the rapid development of white LED technologies. The study of this thesis targets the improvement of thermal stabilities of three nitride phosphors including nitridosilicates (MSiN), oxonitridoaluminosilicates (MSiAlON) and nitridoaluminosilicates (MAlSiN), respectively. The composition-controlled strategies for thermal stability are based on known physical properties. For example, the covalence of Si−C bonds is larger than that of Si−N bonds and the thermal vibrational frequency of Ba2+ cations are smaller than that of Sr2+ cations. These improvement strategies are applied to the anions substitution for non-activator sites or the cations substitution for activator/non-activator sites of nitride phosphors and simutanously maintain the crystal sturcture in the electrical neutrality by charge compensation. In addition, composition-controlled effects for photoluminescence in these three different nitride phosphors are invesigated. Furthermore, we propose the explaining mechanisms for the unexpected photoluminescence phenomena and demonstrate these by the experimental evidences each other. In the first research part, the coexistence of two phases in the middle phase Sr0.6Y1.38Si4N6.6C0.4:Ce3+0.02 and a dominant neighboring-cation effect had been discovered to control the thermal stability of Sr1−xY0.98+xSi4N7−xCx:Ce3+0.02 materials. In the second research part, the decrease in emission energy and the increase in thermal stability with x in Sr0.92−xBaxSiAl2O3N2:Ce3+0.04,Eu2+0.04 system are resulted from a dominant chemical pressure compression effect on the activator sites. In the third research part, the emission and thermal stability of Ca0.99Al1−4δ/3−xSi1+δ+xN3−xCx:Eu2+0.01 (δ = 0.345; x = 0–0.2) red nitride phosphors are well improved by second-sphere-shrinkage effect. The thesis focuses on the research of composition-controlled effects for improving photoluminescence in different nitride phosphors, proposes reasonable mechanisms to elucidate the effects, and provides the corresponding detailed investigations and evidence. We believe that these studies have certain reference values for understanding photoluminescence in other phosphors. In addition, the nitride phosphors with improved thermal stabilities in this thesis also have development potential for white LEDs in the future.

並列關鍵字

nitride ； phosphors ； composition-controlled ； thermal stability ； photoluminescence

參考文獻

References (Chapter 1)

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[1] Ke, W.-C. “Investigation of phosphors with high stability for white light emitting diodes” Master thesis, Department of Chemistry, National Taiwan University, Taipei, 2009.