長餘輝與奈米結構硫氧化釔螢光體之合成與其發光特性之研究

Abstract

本論文分別使用傳統固態法及solvothermal法合成長餘輝與奈米結構的Y2O2S螢光體以及X射線奈米Gd2O2S:Tb3+螢光粉。 在長餘輝螢光體方面，主要係以Mg2+、Ti4+或兩者同時摻入Y2O2S:Eu3+主體內，以觀察其受紫外線照射後之餘輝特性及衰減的變化。本研究發現：在Y2O2S;Eu3+, Mg2+與Y2O2S:Eu3+, Ti4+兩長餘輝材料，Mg2+與Ti4+離子最佳摻雜濃度為3 mol%與2 mol%，餘輝時間達2分鐘，而Y2O2S:Eu3+, Mg2+, Ti4+螢光體之餘輝時間為5分鐘，餘輝強度為三者中最強，餘揮衰減最緩慢。 在奈米結構的Y2O2S螢光體方面，本研究亦探討了Y2O2S:R﹙R＝Pr3+、Sm3+、Eu3+、Tb3+、Dy3+、Er3+﹚之solvothermal法與固態法合成，TEM影像顯示前者螢光體晶粒平均粒徑約為20 nm而後者所合成者約為2-6 μm。 光致發光光譜的探討發現：奈米結構的Y2O2S:R之發光光譜吸收峯波長相對於固態法合成的樣品呈現藍位移，而放射峯波長位置不變，但放射峯強度相對於固態法合成樣品則呈現銳減之現象。

The research is attempted to synthesize long afterglow and nanostructured Y2O2S-based phosphors and X-ray phosphors Gd2O2S:Tb nanoparticles by using solid-state and solvothermal routes, respectively.. To study the effect of activators Mg2+, Ti4+ or both cations on the photoluminescence (PL) and afterglow (AG) properties for Y2O2S phosphors, we have synthesized three series of optimally doped phosphors such as doubly-doped Y2O2S:Eu3+,3%Mg2+, Y2O2S:Eu3+,2%Ti4+ and triply-doped Y2O2S:Eu3+,Mg2+,Ti4+, among which Y2O2S:Eu3+,Mg2+,Ti4+ exhibits the strongest afterglow intensity and slowest decay rate among all samples investigated In addition to the solid-state route, we report the synthesis for Y2O2S:R3+(R = Pr3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+) nanoparticles from a methanolic solution containing stoichiometric amount of Y(NO3) 3．6H2O, thiourea and 1 mole% of R(NO3)3 at 150℃ in a teflon-lined autoclave. The as-prepared Y2O2S:R3+ nanoparticles were found to be poorly crystalline and become well crystalline only when annealed at above 500℃ in an atmosphere of H2S, as indicated by temperature-dependent X-ray diffraction (XRD) studies. Furthermore, diffuse and weak electron diffractions (ED) patterns for the as-prepared Y2O2S:Eu3+ nanoparticles can be indexed as reflections of (112), (203), (205) and (223) for Y2O2S, respectively. The investigations on the effect of microstructure on the luminescence for Y2O2S-based phosphors were carried out by XRD, photoluminescence (PL) and afterglow (AG) spectra, transmission electron microscope (TEM) and ED techniques. The average grain size for Y2O2S:R3+ nanoparticles was determined to be 20 nm, as indicated by TEM micrographs, as compared to that of 2-6 □m for those derived from solid state routes. Furthermore, an apparent blue shift of 6 nm in the wavelength of absorption edge attributed to the quantum confinement effect for as-prepared nanocrystalline relative to bulk Y2O2S:Eu samples was observed, as shown by the PL excitation spectra. On the other hand, almost no difference in the emission wavelengths has been observed in the PL spectra for both the nanocrystalline and the bulk.