納米級鋁酸釔螢光體微粒之製備與特性鑑定

Abstract

螢特性光體的功用與效能與其粒徑大小息息相關，一般而言粉末粒徑小較具有製作大面積螢光幕或薄膜的潛力，且量子效率較佳。本研究之主旨在於探討鋁酸釔超微細子材料製程與其發光我及光譜間之相互關係，並試圖微乳液法控制螢光粉體之晶粒大小與粒徑分布。 本研究是藉由陽離子型的界面活性劑溴化正十六烷基三甲基胺（Cetyl-teimethylammonium bromide, CTAB）形成均相含並R3+、Y3+及Al3+等離子的水╱油相微乳液（W/O microemulsion），再經膠體共沉步驟於水相中生成(Y3-xRx)Al5O12 (YAG:R, R為Ce3+、Eu3+ 、Tb3+)之前驅物。所得的前驅物經980℃高溫澆結，可得YAGR 納米級（nanometer sized）螢光體。利用X 光繞射、掃描及穿透式電子顯微鏡術業分析YAG:R納米晶粒之微結構（如：晶粒形貌與粒徑大小及分佈）。本研究發現YAG:R晶格常數隨R3+離子半徑及添加量的增加而增。我們也探討了添加不同濃度的活化劑對納米級YAG:R螢光體之光致發光（PL）光譜強度與CIE色度座標之影響，並發現隨活化劑種類不同，呈現不同的效應。 與固態合成法、膠體共沉法合成相互比較，微乳液法所得的晶粒最小約可達35nm，比表面積為29.49m2/g。而共沉法所得樣品晶粒約可達80nm，比表面積為6.731lm2/g；固態合成法粒子所得最小約可達0.5μm，比表面積為6.731lm2/g。以同質量各式樣品進行結果PL發射光譜強度量測，以微乳液法所得樣品最高，膠體共沉法的次之，而固態合成法的最弱。以衰減期而言，以雙系微乳液法製作的Y2.9Tb0.1Al5O12螢光體約12ms最長，單系微乳液法的9至10次之，共沉法的7-8ms 再次之，固態合成法則約為3ms 左右。螢光猝冷溫度隨摻加活化劑種類不同而異，約在300至330K之間。此結果顯示其發光特性如我們所預期，受表面積與晶粒大小影響十分顯著，此說明了微乳液法為何適合用於生產高表面積、高亮度、長時效的YAG:R螢光體之主要理由。

There have been active researches on garnet phosphors for their potential applications in manufacturing large phosphor screens or thin phosphor film and better quantum efficiency. This research is attempted to develop new synthetic routes and investigate their effects on the luminescent properties of garnet phosphor materials. Microemulsion methods demonstrates an efficient route to prepare phosphors with controled grain size and narrow size distribution. Rare earth-activated (Y2.9R0.1)Al5O12 (YAG:R) (R=Eu, Tb and Ce) phosphor nanoparticles have been synthesized at 980℃ in air, by employing a W/O (water-in -oil) microemulsion method with CTAB (cetyltrimethyl-ammonium bromide) as a surfactant, and chlorobenzene as an organic phase for micelle formation. Gel-precipitation process takes place in aqueous phaes containing R3+, Y3+ and Al3+ ions. X-ray diffraction (XRD), SEM, TEM and STEM are used to analysze the microstructure of YAG:R nanoparticles (e. g. , grain size, grain morphology and grain size distribution). Cell parameters of YAG:R nanoparticles increase with increasing R3+ radius and dopant concentration. The concentration dependence of photoluminescence (PL) intensity and the position of CIE chromaticity coordinate diagram has also been investigated. Average specific surface area of YAG:R nanoparticles dervied from microemulsion route was determined to be 29.5m2/g compared to 8.9 and 6.7m2/g obtained from solid state and gel-coprecipitation methods, respectively. The average grain size for sample obtained from microemulsion, solid state and gel-coprecipitation method was found to be 35nm, 80nm and 0.5μm, respectively. The PL intensity of phosphors was found to be highly dependent on the preparation methods. Fluorescence decay time values of as prepared YAG:R nanoparticles obtained from double and single microemulsion method was found to be ca. 12 ms and 10 ms, respectively, compared to 8 ms and 3 ms for samples obtained from solid state and gel-coprecipitation methods. The quenching temperature of as-perpared YAG:R nanoparticles was determined to be ca. 300~330K depending on the types of activator ions.