Abstract: Aseries of Y_1-x Eu_x Ta_1-y Nb_y O₄ ( x =0—0.20, y =0—1.00) are synthesized by a modified solid state reaction method. When the concentration of NbO₄^3- in yttrium tantalate is low, the structure of these systems is M' type YTaO₄. With increasing concentration of NbO₄^3-, its structure completely changed from M' type YTaO₄ to fergusonite YNbO₄. Under UVexcitation, the emission spectra of YTaO₄:Nb,Eu consist of two parts, the emission band between 300—450 nm is the charge transfer emission of NbO₄^3-, and the sharp line emissions in the range of 500—720 nm originate from the transition of electrons in 4f shell of Eu ³⁺. The main peak at 612.7 nm can be ascribed to the Eu ³⁺⁵ D₀→ ⁷F₂ transition and shows a strong red emission. Fixing the concentration of Nb ⁵⁺ and Eu ³⁺ separately, and changing the concentration of another ions, the luminescent properties of Y_1-x Eu_x Ta_1-y Nb_y O₄ will change rapidly. The difference of luminescence is originated from different structures. The excitation spectra of NbO₄^3- emission ( λ =400 nm) in YTa _0.98 Nb_0.02 O₄ is a strong excitation band peak at 235 nm. In fact, the band is composed of charge transfer excitation of TaO₄^3- and charge transfer excitation of NbO₄^3-. The excitation spectra of Eu ³⁺⁵D₀→ ⁷F₂ transition emission have two parts, the sharp lines between₃₀₀—600 nm and wide band between₂₀₀—300 nm. The sharp lines originate from Eu ³⁺ f-f electron transitions, and the wide band includes both charge transfer excitation of TaO₄^3- and NbO₄^3-, and charge transfer excitation of Eu ³⁺. The excitation spectra of NbO₄^3- emission ( λ =400 nm) in Y_0.99 Eu_0.01 Ta_0.98 Nb_0.02 O₄ is also a strong band, in which there also exists a charge transfer excitation of TaO₄^3- and a charge transfer excitation of NbO₄^3-. The strong evidence from excitation spectra, emission spectra of this system show that there is a energy transfer from host lattice to activator in the process of luminescence.

Key words: Luminescence, Yttrium tantalate, Niobate