Abstract
Yttrium silicate powders doped with Eu3+ and codoped with Eu3+ and Yb3+ were prepared by combustion synthesis. The x-ray powder diffraction data showed the presence of Y2SiO5 and Y2Si2O7 crystalline phases. Singly doped (1 wt %) sample illuminated with ultraviolet light (λ=256 nm) showed the characteristic red luminescence corresponding to D50→F7J transitions of Eu3+. The Judd–Ofelt intensity parameters were calculated from experimental data and the radiative and nonradiative relaxation rates were estimated. The results showed that the nonradiative relaxation rate is smaller in yttrium silicate compared to yttrium oxide powder, a reference material, prepared under similar conditions. Codoped samples were exposed to near-infrared laser excitation (λ=975 nm) and the red luminescence of Eu3+ was also observed. In this case, the luminescence is achieved due to a cooperative upconversion (CUC) process involving energy transfer (ET) from pairs of ytterbium ions to europium ions. The ET rate was estimated by fitting a rate equation model with the dynamics of CUC red emission.
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