UV–vis absorption shift of mixed valance state tungstate oxide: Ca 0.72 La 0.28 WO 4

CaWO4 and Ca0.72La0.28WO4 samples were synthesized via mild hydrothermal method at 180°C. Composition, phase purity, morphology and W element binding energy were characterized by induced couple plasma atomic emission spectrum (ICP-AES), powder x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray energy dispersive spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). UV–vis absorption spectroscopy shows absorption peak shift due to La3+ doping, which induced to the presence of mixed valence states of W5+ and W6+ in scheelite-type structure compound. Hence, blue shift of UV–vis absorption from 350nm to 405nm was observed in La3+-doped calcium tungstate.