奈米級硫氧化釓螢光體水熱法合成與發光特性之研究

Abstract

本研究利用簡易的水熱法裝置配合高溫(500-1000℃)的硫化退火兩階段製程，成功地合成三系列稀土離子(如: Tb3+, Pr3+, Eu3+)激活Gd 2O2S奈米螢光體，並利用X射線繞射、螢光光譜儀和掃描、穿透式電子顯微鏡鑑定其發光與微結構特性。 研究結果顯示水熱合成Gd(OH)3前驅物時之反應，pH值和溫度分別是決定產物Gd 2O2S:R晶粒型態和粒徑大小之重要製程參數。當將水熱溶液中之pH值從8增加到10時，可觀測到奈米前驅物Gd(OH)3晶粒轉變為奈米棒之不尋常變化。本研究所合成奈米Gd 2O2S:R晶粒之直徑約80 nm，而奈米Gd 2O2S:R棒則具有10之長寬比，其長度與直徑分別為200nm和20 nm。 另一方面，本研究也利用傳統固態法製備微米級Gd 2O2S:R螢光體，並和水熱與退火兩階段製程所合成之奈米Gd 2O2S:R比較，以探討發光特性與微結構間之相互關係。

In this research we have successfully synthesized three series of Gd2O2S:R ( R = Tb3+, Pr3+, Eu3+) nanophosphors via a two-step process by utilizing simple hydrothermal apparatus at 140-200℃, followed by a annealing under H2S atmosphere at 500-1000℃. The correlation between phase purity, photoluminescence and microstructure of Gd2O2S:R nanophosphors were then characterized by X-ray diffraction, spectrofluorimeter, scanning microscope (SEM) and transmission microscope (TEM) techniques. Our research indicates that the pH values and temperature adopted in the hydrothermal synthesis to form nanocrystalline Gd(OH)3 precursor are the most important processing parameters in determining the grain morphology and sizes of Gd2O2S:R nanophosphors. The morphology of nanocrystalline Gd(OH)3 precursor was observed to change from granular to rod-shaped when pH was allowed to vary from 8 to 10. The average diameter of granular Gd2O2S:R was found to be ca. 80 nm, whereas the aspect ratio (c/a) for Gd2O2S:R nano-rods was found to be 10 with length and diameter of 200 nm and 20 nm, respectively, as indicated by TEM investigations. On the other hand, the luminescence and microstructure for bulk and nano-crystalline Gd2O2S:R phosphors prepared from solid-state and two-step hydrothermal routes, respectively, were also compared.