Hydrothermal synthesis and luminescence of CaMO4:RE3+ (M=W, Mo; RE=Eu, Tb) submicro-phosphors

Submicrometer crystalline CaMO4:RE3+ (M=W, Mo; RE=Eu, Tb) phosphors with a sheelite structure have been synthesized via the hydrothermal process, which were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray-excited luminescence (XEL), UV–vis diffuse reflectance spectra (UV–vis DRS) and scanning electron microscopy (SEM), respectively. The XRD patterns show that both CaWO4 and CaMoO4 have the same structure with space group I41/a. The SEM images indicate that the optimal hydrothermal temperature is 120 °C for the particles that aggregate with the increase of temperature. The bands ranging from 380 to 510 nm in the XEL spectra of CaWO4:Eu3+ can be attributed to the charge transfer state from the excited 2p orbits of O2− to the empty orbits of the central W6+ of the tungstate groups. The comparison between photoluminescent lifetimes and quantum efficiencies of the two phosphors was also investigated in detail.