發光二極體用氮化物及矽酸鹽螢光材料之製備與特性分析

Abstract

白光發光二極體因具有壽命長、堅固耐用及節能環保之優點，而具有取代白熾燈泡或日光燈管等傳統光源之可能性，因此被視為是下個世代具有潛力的照明光源之一。然而，過去市面上的白光發光二極體因螢光粉體缺乏紅色波段的放光，使得所合成之白光多屬於冷白光且演色性差。為了克服此缺失，多種替代方案已被提出並進行相關研究。其一為在傳統的藍光LED晶片激發黃光螢光材料中添加紅光螢光材料，以補足其紅光波段之不足而可合成出演色性較佳之白光。其二為以紫外光LED晶片同時激發藍光、綠光與紅光之三色螢光材料，預期也能合成出高演色性之白光。本論文將就此兩方法為主軸進行研究與探討。 論文第一部分選擇三元之氮化物(Sr2Si5N8)作為螢光材料之主體。在單獨摻雜銪離子(Eu2+)的情況下，當激發光波長固定在420 nm時，可觀察到峰值約在615 nm之橘紅光放光。當將銪離子與激活劑離子共同摻雜到主體時，在相同的激發光下，可觀察到橘紅光之放光有增強的趨勢。藉由銪離子與激活劑離子共添加的螢光粉體其最高放光強度經量測較單獨摻雜銪離子的螢光粉體增加43%。研究結果解釋藉由銪離子與激活劑離子的共摻效應，可有效增強螢光粉體的放光強度，進一步增加此螢光粉體在白光發光二極體中的實用性。 論文第二部分為新型矽酸鈣鑭螢光材料之研究，其化學組成為Ca3La6(SiO4)6。在單獨摻雜鈰離子(Ce3+)與鋱離子(Tb3+)時，分別具有420 nm及545 nm 之特徵放光。當鈰離子與鋱離子共添加於主體時，隨著鋱離子添加量的增加，經由能量轉移之機制，可觀察到鈰離子所產生的藍光強度下降而鋱離子所產生的綠光強度上升。研究結果說明Ca3La6(SiO4)6: Ce3+, Tb3+螢光粉體之放光顏色可藉由調整鋱離子的添加量，由藍紫光移動到綠光，顯示其為適用於發光二極體之一具有潛力的新型可調光式螢光材料。

White light-emitting diodes (LEDs) have become a promising luminescent light source in the next generation to substitute for the conventional incandescent and fluorescent lamps. However, the white light produced from the conventional type of white LEDs lacks sufficient emission in the red range, therefore leading to the so-called “cold white light” with a low color rendering index. To overcome the drawback, several alternative approaches have been proposed and been underway now. One of the approaches is to integrate the conventional type of white LEDs with red-emitting phosphors for generating white light with high color rendering index. Another approach is to combine ultraviolet LEDs with tricolor-emitting phosphors, which is also expected to produce the white light with high color rendering index. The above-mentioned alternative approaches are mainly focused in this study. In the first section, nitride-based Sr2Si5N8 was selected as the host material for preparing red-emitting phosphors. Under the blue excitation at 420 nm, solely Eu2+-doped Sr2Si5N8 phosphors displayed a broad emission band peaking at around 615 nm. When Eu2+ and sensitizer ions were co-doped into Sr2Si5N8, it was observed that the emission intensity in the red region tended to increase and was found to be enhanced at most 43% as compared with that of solely Eu2+-doped Sr2Si5N8 phosphor. The results demonstrate that the emission intensity of the phosphors could be enhanced via incorporating Eu2+ and sensitizer ions into Sr2Si5N8, further improving the applicability of the phosphors for white LEDs. In the second section, silicate-based Ca3La6(SiO4)6 was chosen as the host material, while Ce3+ and Tb3+ ions were selected as the doping ions. The solely Ce3+-doped and Tb3+-doped Ca3La6(SiO4)6 phosphors exhibited emissions at 420 nm and 545 nm, respectively. When Ce3+ and Tb3+ ions were co-doped into Ca3La6(SiO4)6, the emission spectra showed a combination of the emission band originated from Ce3+ ions and the emission lines generated from Tb3+ ions. With the increasing doping content of Tb3+ ions, the emission intensity of Ce3+ ions in the blue region decreased monotonically, whereas that of Tb3+ ions in green region considerably increased. The results reveal that the emitting colors of the phosphors could be shifted from purplish blue to green via controlling the doping content of Tb3+ ions. Ca3La6(SiO4)6: Ce3+, Tb3+ phosphors are the prospective color-tunable materials for applications to light emitting diodes.