Structure characterization, optical and photoluminescence properties of scheelite-type CaWO4 nanophosphors: Effects of calcination temperature and carbon skeleton

Abstract

The synthesis of self-activating tungstate phosphor is always associated with complicated procedures, and it is still challenging to adjust and control their phase transition, optical, and photoluminescence properties by a gamma-ray irradiation assisted polyacrylamide gel method. Scheelite-type calcium tungstate (CaWO4) nanophosphors with different phase purity were synthesized by a wet chemistry method and the phase transition, optical, and photoluminescence properties of as-prepared samples were systematically studied. The calcination temperature and carbon skeleton have significant impact on the phase structure, crystalline size, optical and photoluminescence properties of CaWO4 nanophosphors. The crystallite size of CaWO4 nanophosphors increases with the increasing of calcination temperature. Below 600 °C, the Eg value of CaWO4 products increases with the increasing of calcining temperature, while the Eg value showed the opposite trend for the CaWO4 xerogel sintered at above 700 °C due to the effects of crystallinity and residual carbon skeleton. The color and optical properties shows that the pure CaWO4 is a potential white pigment. The photoluminescence spectra show that the CaWO4 products obtained by calcining the CaWO4 xerogel at different temperatures have a major emission band around 428 nm and a weak emission peak at 386 nm with the excitation wavelength of 240 nm. The intensity of emission peak at 428 nm increase first and then decreases with the increasing of calcining temperature. The emission peaks at 428 and 386 nm can be ascribed to the 1T2 to 1A1 optical transition of electrons within [WO4]2- anions and the defect or carbon skeleton, respectively.