新穎鹼土多磷酸鹽螢光體合成、發光特性與能量轉移之研究

Abstract

本研究利用固態合成法製備Ca9Al(PO4)7、Ca9Ga(PO4)7、Ca9In(PO4)7、Sr9In(PO4)7等鹼土多磷酸螢光體，分別摻入Ce3+、Tb3+及Ce3+/Tb3+共摻雜，並以XRD和螢光光譜進行其結構與發光特性的鑑定，主旨在開發可用於冷陰極管(CCFL)之新穎組成的螢光體。 本研究皆利用汞蒸氣主要放射波長254nm激發，在第一部分單摻Ce3+螢光體中，Ca9M(PO4)7 (M = Al, Ga, In)放光位置皆在365nm左右，且隨著摻雜濃度的提升，有紅位移的現象產生；Sr9In(PO4)7則放出375nm的紫藍光。第二部分摻雜Tb3+螢光體皆具有Tb3+特徵放射峰541nm的黃綠光。第三部分則延伸討論Ce3+/Tb3+共摻雜螢光體之能量轉移機制，當加入Ce3+做為敏化劑後，可有效提升黃綠光之放光強度，且全系列螢光體皆藉由共振型偶極－偶極機制進行能量轉移。最後探討其熱穩定性可得知Ca9M(PO4)7 (M = Al, Ga, In)系列在高溫時具有較佳的熱穩定性，Sr9In(PO4)7則有放光強度衰減現象。

In an attempt to develop new phosphors for cold cathode fluorescent lamps (CCFL), four series of polyphosphate phosphors, Ca9Al(PO4)7:R, Ca9Ga(PO4)7:R, Ca9In(PO4)7:R, Sr9In(PO4)7:R (R = Ce3+ or Tb3+) and Ca9M(PO4)7:R:Ce3+,Tb3+ (M = Al, Ga, In), were synthesized and investigated. X-ray powder diffraction was used to verify the phase purity and crystal structures; photoluminescence (PL) spectra and thermal quenching measurements were used to study the luminescence performance of the phosphors. The first part of this research investigates Ce3+-activated Ca9M(PO4)7 (M = Al, Ga, In) phosphors which show broad band excitation and ultraviolet emission. The emission wavelength was found to exhibit a red shift trend with increasing Ce3+ dopant content; on the other hand, Sr9In(PO4)7:Ce3+ does not iii behave similarly. Secondly, we have also investigated the series of Tb3+-activated phosphors, which show characteristic weak green emission of Tb3+ ion attributed to the forbidden f-f transition. To improve the luminescence efficiency, along with Tb3+ we have codoped Ce3+ as a sensitizer and further investigated the luminescence efficiency and the mechanism of energy transfer from Ce3+ to Tb3+. The PL intensity of Tb3+ was demonstrated to be greatly improved and the energy transfer was determined to be a resonance electric dipole-dipole interaction for all four series of Ce3+/Tb3+-codoped phosphors. Finally, the temperature dependence of the PL intensity or thermal quenching for all four series of polyphosphate phosphors was also investigated, we found that Ca9M(PO4)7:Ce3+,Tb3+ (M = Al, Ga, In) series of phosphors show superior thermal quenching stability at high temperature, yet the PL intensity of Sr9In(PO4)7:Ce3+,Tb3+ was found to decrease appreciably with increasing temperature in the temperature range of 25-250℃.