氮氧化物螢光材料之結構與光學特性探討

Abstract

第一部分之研究主要著重於活化中心與螢光粉主體晶格中之被取代陽離子間之陽離子尺寸錯位效應，許多過往文獻揭示可利用不同陰陽離子取代之方式調整螢光粉放光特性，但許多基底機制並未被清楚闡述，且此些調整放光之方式只可調整放光能量往同一波長方向。此部分之研究結構為M2Si5-xAlxN8-xOx:Eu (M = Ca, Sr, Ba)，於此結構中當M為Ba時會發生較大之紅位移，當M為Sr時發生較小之紅位移，但當M為Ca時則轉為較大之藍位移，故本研究提出與氮/氧陰離子相關之陽離子尺寸錯位機制與相對應之證明，另此機制亦可調控螢光之熱淬熄現象。此二特性除可被陽離子尺寸錯位模型所解釋，亦對於發光二極體元件之應用極為重要。 第二部分之研究主要著重調整Tb3+為活化中心之螢光粉放光特性，此部分之研究結構為Ba2.89Si6O12N2:Tb0.11，於此結構中改變激發光源從紫外光至真空紫外光，可得綠與藍色之可調與可逆放光特性，故本研究提出顏色反轉機制、躍遷模型與相對應之證明，此效應對Tb為活化中心之螢光粉於電漿顯示器或螢光燈之應用極為重要，且所提出之機制可利用組態座標模型解釋顏色反轉之現象。 第三部分之研究主要著重發展紫外光發光二極體激發之高效率螢光粉，此部分之研究結構為Ba3Si6O12N2:RE (RE = 稀土金屬)，於此結構中可為單(Eu)或雙(Ce與Eu)活化中心摻雜之螢光粉，其中兩重要之螢光特性為：(1) Eu為活化中心之螢光粉於高熱環境中之光譜位移現象，(2) Ce與 Eu為活化中心螢光粉之高效率能量轉換特性。此外利用綠色Ba3Si6O12N2:Eu螢光粉與其他藍與紅螢光粉可組成紫外光激發之白光發光二極體。上述特性令此氮氧化物不僅為一特殊之研究結構，更可令其作為於紫外光發光二極體應用中為一藍或綠之發光組成。

This study focuses on the development of an effect of cation-size mismatch strain between the dopant (activator) and substituted objective (cation in host lattice). Several chemical tunings have been reported; however, their underlying mechanisms remain unclear. In addition, these chemical tunings invariably shift the energy in a group of comparable materials in the same way, e.g., a consistent red shift. Our materials, M2Si5-xAlxN8-xOx:Eu (M = Ca, Sr, Ba), show a large red shift for M = Ba and a small red shift for Sr, but exhibit a large blue shift for Ca. Thus, we propose a mechanism for this size mismatch tuning based on local nitride/oxide anion clustering and supporting evidence. Thermal quenching of photoluminescence is also tuned by cation mismatch, Moreover, both effects are important for light-emitting diode (LED) devices, and both mismatch tuning effects are explained by our size-driven anion clustering model. In the second part, an unreported phenomenon for tuning the emission properties of Tb3+ activators is discussed. Our material, Ba2.89Si6O12N2:Tb0.11, shows the tunable and reversible properties in the green/blue emission under UV to VUV radiation excitation. Thus, we propose a possible mechanism for this color reversal control based on a specific transition route as a color-tunable switch at the UV/VUV range and supporting evidence. This effect is significant for Tb-activated phosphors in PDP or fluorescent lamp devices, and the color-reversal effect is explained by our configurational coordinate model. In the third part, we develop a highly efficient green phosphor for using in a practical UV-LED device. The highly efficient Ba3Si6O12N2:RE (RE = rare earth metal) is composed of single-doped and co-doped phosphors with Eu and Ce rare earth metals. The possible mechanisms of the two important photoluminescence properties are proposed for LED device-used phosphors, namely, (1) spectral shift in a high temperature environment in the Eu-doped phosphor and (2) highly efficient transfer property in the Ce/Eu co-doped analogue. The UV-WLED device is fabricated by green Eu-doped Ba3Si6O12N2 and other blue and red phosphors. The distinctive properties of this oxynitride parent structure make it an interesting subject for research and as a candidate for a blue/green component for UV-LED applications.