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

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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.