Characterization and photoluminescence properties of AgLn(MoO4)(WO4): Novel silver based scheelite-type compounds

Novel silver based rare earth tungstate-molybdate, AgLn(MoO₄)(WO₄), with scheelite-like structure have been synthesized by ceramic method. The crystal structure, luminescence properties and fluorescence lifetime of a series compounds were investigated systematically. Some special characteristic emission bands were observed which can be attributed by the energy transfer between Ag⁺ and Ln³⁺ ions. Especially, AgDy(MoO₄)(WO₄) and AgHo(MoO₄)(WO₄) phosphors can emit white light under near-UV excitation, with chromaticity coordinates at about (0.3605, 0.3652) and (0.3559, 0.3479) respectively. Fluorescence lifetime of Eu³⁺ and Tb³⁺ were measured in both room temperature and liquid nitrogen temperature. In excitation spectra, the evident blue shift of charge transfer (CT) band in the case of liquid nitrogen temperature indicates that the effective W-O and Mo-O covalence bond is lower at liquid nitrogen temperature which can be caused by the lower wave function overlaps of W-O and Mo-O. Furthermore, low temperature showed positive effect for longer fluorescence lifetime.