鄰近陽離子取代效應調控CaAlSiN3:Eu之活化劑格位

Neighboring-cation Substitution-driven Remote-controlled Activator in CaAlSiN3:Eu Lattice

王筱姍(Siao-Shan Wang)

指導教授 ： 劉如熹

國立臺灣大學/理學院/化學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.10415

摘要

紫外光-藍光發光二極體激發之高效率紅色螢光粉為生活中重要照明來源，尤其須具極佳本質特性，例如化學與熱穩定性佳。相較於氧化物螢光粉，氮化物螢光粉之放光通常較紅位移且熱/化學穩定性較佳，乃因其共價性較大，例如：Sr2Si5N8:Eu2+ 與 CaAlSiN3:Eu2+。
陽離子取代通常可用於調控其光學特性與熱穩定性之最適化，但相關之研究與機制尚未被清楚地瞭解，故本研究利用鄰近陽離子取代可系統性地調控CaAlSiN3:Eu2+系列之熱特性。當三價陽離子(如La3+)取代於其中之Ca2+格位時，其熱穩定性隨之變差。反之，以一價陽離子(如Li+)取代時，則熱穩定性提升。由螢光壽命之衰減光譜亦可得知陽離子取代之光譜特性變化。
鄰近陽離子取代與調控其中之Al3+/Si4+ 之組成作為電荷平衡，使活化劑離子Eu2+ 可選擇性地取代於特定Ca2+ 格位中。當三價陽離子取代時，其Eu2+離子位於鄰近Al3+/Si4+平均之陰離子團配位中，然而當一價陽離子取代時，其將位於Si-rich之配位環境中，故其放光光譜特性可受陽離子取代而調控。此機制可被廣泛應用於螢光材料，藉此有效地調控其光譜特性。

關鍵字

發光二極體 ； 螢光粉 ； 螢光光譜 ； 熱穩定性 ； 鄰近陽離子取代

並列摘要

Red phosphors with high efficiency in general, and those with excellent intrinsic property in particular, excited by ultraviolet or blue light-emitting diodes are significant white light sources for our daily life. Nitride-based phosphors, such as Sr2Si5N8:Eu2+ and CaAlSiN3:Eu2+, are commonly more red-shifted in photoluminescence and have better thermal/chemical stability than oxides because of high covalency.
Cation substitutions are usually performed to optimize photoluminescence and thermal quenching behavior. However, the underlying mechanisms are unclear in most cases. Hence, we show that neighboring-cation substitution systematically controls temperature-dependent photoluminescence behavior in CaAlSiN3:Eu2+ lattice. The trivalent cation substitution at the Ca2+ site degrades the photoluminescence in high temperature environment, but the substituted cation turning monovalent achieves better thermal stability. The Neighboring-cation control of lifetime decay is also observed.
A remote control effect that guides Eu2+ activators in selective Ca2+ sites is proposed for neighboring-cation substitution while compositional Al3+/Si4+ ratio adjusts to the valance of Mn+ (n = 1-3) cation. In this effect, the Eu2+ activators are surrounded with anion clustering neighbored with M3+-dominant and Si4+/Al3+-equivalent coordination when M is trivalent (e.g La3+), but shift to the site where surrounded anion clustering neighbor with M+-dominant and Si-rich coordination when M is monovalent (e.g Li+). This mechanism can efficiently tune optical properties especially thermal stability and could be general to luminescent materials, which are sensitive to local valence variation in local environments.

並列關鍵字

Light-emitting diode ； phosphor ； photoluminescence ； thermal stability ； Neighboring-cation substitution

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