Rietveld refinement and optical properties of SrWO4:Eu3+ powders prepared by the non-hydrolytic sol-gel method

We investigated the effect of annealing time on the structure and optical properties of SrWO4:Eu3+ powders prepared by the non-hydrolytic sol-gel method and heat treated at 800 degrees C for 2, 4, 8 and 16 h. Thermogravimetric and differential thermal analyses revealed that SrWO4: Eu3+ powders were obtained at about 800 degrees C. X-ray diffraction patterns and Rietveld refinement data confirmed that all powders had a scheelite-type tetragonal structure. Micro-Raman and Fourier transform infrared spectra indicated structural order at short range and anti-symmetric stretching vibrations of O-W-O bonds associated with tetrahedral [WO4] clusters. Optical properties were investigated by ultraviolet-visible (UV-vis) diffuse reflectance, and photoluminescence (PL) data which provided the evolution of quantum efficiency (eta) and lifetime (tau). UV-vis spectroscopy evidenced intermediate energy levels within the band gap of SrWO4:Eu3+ powders. PL properties validated that the Eu3+ electric-dipole (D-5(0)-> F-7(2)) transition in PL emission spectra was dominant which proved that Eu3+ ions were positioned in a site without an inversion center. [(D-5(0)-> F-7(2))/(D-5(0)-> F-7(1))] band ratios showed that Eu3+ ions were located in a low symmetry environment. The PL emission,. and t proved the dependence on the annealing time in the behavior of SrWO4:Eu3+ powders with a higher relative emission PL intensity as well as higher. and t values related to other samples when heat treated at 800 degrees C for 8 h.