PDF《博士学位论文公示材料》

2、 NaY(WO4)2 和NaLu(WO4)2 在紫外光激发下均表现出钨酸根基团的蓝色本征发光.利用钨酸根发射带与 Eu3+ 离子激发带的部分重 叠,在紫外光激发下实现了 Na(Y1-xEux)(WO4)2(x=0.001~0.01)荧光粉的蓝~红荧光色调控,分析了 具体的能量过程,并在 x=0.4 时获得了白色荧光.经600 o C 煅烧正交相 NaLuW2O8?2H2O:Yb/Ln 前驱体 获得了四方相 NaLu(WO4)2:Yb/Ln(Ln=Ho、Er、Tm)上、下转换荧光粉.在978 nm 近红外激光泵浦 下,发现 Yb3+ 可有效敏化 Ho3+ 、Er3+ 和Tm3+ 在NaLu(WO4)2 晶格中的上转换发光,明确了各体系上转 换发光的过程和机理;

发现 Ho3+ 、Er3+ 和Tm3+ 在各自最佳激发波长激发下分别呈现良好的绿色(545 ―2― nm) 、绿色(500~575 nm)和蓝色(455 nm)下转换荧光发射.利用 Dieke 能级图分析了上、下转换 发光过程的区别及三种激活离子下转换发射光谱的特征. ―3― 论文摘要(英文) This Doctoral Dissertation focuses on rare-earth (RE) tungstates, with comprehensive investigation into hydrothermal synthesis, crystal structure and up-/down-conversion luminescence property. The effect of hydrothermal parameter on product property was systematically investigated through regulating the solution pH and [WO4]2- /La3+ molar ratio in the wide ranges of 4-13 and 0.5-3, respectively, and the underlying mechanism was interpreted from the solution chemistry of La3+ and tungstate ions. Four types of La tungstates were successfully obtained in a phase-pure form by calcining their hydrothermal precursors. Phase and morphology evolution, crystal structure and properties of Eu3+ emission were comparatively investigated for the four compounds. Extension of NaRE(WO4)2 synthesis to the full spectrum of lanthanide elements (RE=La-Lu, excluding Pm) and Y has been successfully achieved, and the intrinsic effects of lanthanide contraction on the structural features, phase composition and crystal morphology were clarified. The crystallization kinetics was analyzed with NaLa(WO4)2 as an example. Morphology regulation of NaRE(WO4)2 with tartrate ions was also discussed. Meanwhile, NaLuW2O8?2H2O and NaLaW2O7(OH)2?H2O were hydrothermally synthesized as new types of tungstates with novel structural features, and their crystal structures were deciphered with the Rietveld technique. The self-activated photoluminescence of NaRE(WO4)2 (RE=Gd, Y and Lu) compounds and the up-/down-conversion luminescence of the phosphors doped with RE3+ activators were investigated. The main achievements are summarized as follows. (1) Phase and chemical composition of the product was found to be affected by solution pH (4-13) and the initial [WO4]2- /La3+ molar ratio (0.5-3), and the average W/La molar ratio of the product increased with decreasing pH or increasing [WO4]2- /La3+ molar ratio. Meanwhile, the optimal pH value and the minimum [WO4]2- /La3+ molar ratio for the hydrothermal crystallization of NaLa(WO4)2 were found to be

8 and 3, respectively. The four La tungstates of La2W3O12, La2W2O9, La14W8O45 and La6W2O15 were obtained by calcining their hydrothermal precursors. The excitation and emission of Eu3+ in the four compounds were found to be affected by the host lattice, and La2W3O12:Eu phosphor exhibited optimal luminescence properties. (2) Crystal structure, phase composition, morphology and infrared responses of the products obtained through hydrothermal reaction under [WO4]2-/RE3+ molar ratio of 3:1, pH=8 and

200 oC for

24 h were found to be closely related to the type of RE. The hydrothermal products are the scheetlite-type NaRE(WO4)2 for the larger RE3+ of RE=La-Dy (including Y), the NaREW2O8?2H2O new compound for the smaller RE3+ of RE=Er-Lu, and a mixture of the two phases for RE=Ho. The Ho-Lu product transformed into NaRE(WO4)2 by calcination at