Lanthanide Ion Induced Phase Decomposition of Tetragonal CaWO4

Abstract Undoped and europium (Eu 3+ ) doped CaWO 4 samples were prepared at room temperature using co-precipitation method and investigated for their thermal stability by annealing at different temperatures, namely 300, 500, 700 and 900 °C in air. It is observed that incorporation of Eu 3+ ions destabilizes CaWO 4 lattice and favors its decomposition at elevated temperatures. Powder X-ray diffraction (XRD) studies confirmed that as-synthesized CaWO 4 : 1% Eu 3+ remains stable up to an annealing temperature of 500 °C, and above that it partially decomposes into WO 3 phase. Unlike this, undoped CaWO 4 remains stable under similar annealing conditions. Photoluminescence, UV-Visible, and infra-red absorption studies provide important evidence for partial decomposition of CaWO 4 : 1% Eu 3+ into its constituent oxides upon annealing at temperatures above 500 °C.