Directed synthesis, growth process and optical properties of monodispersed CaWO4 microspheres via a sonochemical route

Abstract

Monodispersed calcium tungstate (CaWO₄) microspheres were synthesized successfully via a sonochemical process in deionized (DI) water. The functional group and phase formation analyses were carried out using Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively. XRD revealed that all samples were of pure tetragonal scheelite structure. FT-IR and Raman analysis exhibited a W–O stretching peak of molecular [WO₄]²⁻, which related to the scheelite structure. The effect of ultrasonic irradiation times in the sonochemical process was investigated briefly for 1, 5, 15 and 30 min. The shape of the particles was revealed as spherically monodispersed with narrow size distribution and uniform features at the ultrasonic time of 5 min. This study also found that the spherical surface was composed of tightly packed nanosphere subunits. A possible mechanism for the formation of CaWO₄ powders with a different ultrasonic time was discussed in detail. Optical properties showed blue light emission at a wavelength of around 420 nm and an optical energy gap (E_g) value of 3.32–3.36 eV.