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 (FTIR), 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 degrees 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. (C) 2008 Published by Elsevier Inc.