Synthesis and characterization of a Ce3+ trivalent scheelite-type double tungstate by solid state method

Abstract

The trivalent cerium silver tungstate, AgCe(WO4)2, with scheelite-like structure has been synthesized by solid-state method despite the relatively high instability of the trivalent Ce ion. This behavior could be explained by the redox properties of Ag2O in the solid state reaction at high temperature in air, which stabilizes the trivalent valence state. X-ray diffraction analysis was carried out and the refinement was performed in the tetragonal S.G. I 41/a (No. 88). Initially differential thermal analysis (DTA) and thermal gravimetric (TG) were used to analyze the reaction process and chemical mechanism. High temperature X-ray diffraction was introduced in to investigate the thermal stability and phase transition properties. It is found that AgCe(WO4)2 can be decomposed into Ag2W2O7 and Ce2(WO4)3 at temperature range of 500 °C – 700 °C. No phase transition was observed up to 900 °C from room temperature. The results of magnetic susceptibility measurement give confirmed evidence that the trivalent cerium cation existed in the compounds Ag(1+x) Ce(1-x)(WO4)2 (x from 0 to 1/3), and no transition from trivalent Ce3+ cation to tetravalent Ce4+ cation was observed even with decreasing cerium concentration. The fluorescence properties of Eu3+ and Tb3+ doped AgCe(WO4)2 were investigated. It is found that Tb3+ is qualified as a local structure probe rather than Eu3+ in the AgCe(WO4)2 compound considering the quenching mechanism which probably due to the metal to metal charge transfer between Ce3+/W6+.