Hydrothermal synthesis and luminescence of CaMO 4:RE 3+ ( M=W, Mo; RE=Eu, Tb) submicro-phosphors

Abstract

Submicrometer crystalline CaMO 4:RE 3+ ( 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 CaWO 4 and CaMoO 4 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 CaWO 4:Eu 3+ can be attributed to the charge transfer state from the excited 2 p orbits of O 2− to the empty orbits of the central W 6+ of the tungstate groups. The comparison between photoluminescent lifetimes and quantum efficiencies of the two phosphors was also investigated in detail.