Optical spectroscopy of rare earth-doped oxyfluoro-tellurite glasses to probe local environment

TeO 2 -based glasses with a general formula 65 TeO 2 - 5 BaF 2 - 30 ZnF 2 (TBZ) (in mol%) were prepared by usual melt quenching technique. Three mol% of europium (Eu) or erbium (Er) were added to the prepared glass at the expense of TeO 2 . Raman, photoluminescence (PL), UV–visible absorption studies were carried out on the glass samples. Raman spectra of the undoped and doped glasses were analysed using the peak shift and the intensity variation along with full width at half-maximum (FWHM). It was found that Eu-doped TBZ glass has a greater tendency towards depolymerizing the glass matrix by influencing the conversion of TeO 4 to TeO 3 units compared to Er-doped and undoped glasses. PL spectra of the glass samples show emission due to different possible transitions. Position of the peak of the de-convoluted spectra shows the position of the particular Stark component and the FWHM is a measure of the inhomogeneous broadening. The UV–visible absorption spectra are used to calculate the optical density and to determine the band edge of the glass samples by fitting to the Mott equation. It is seen that Eu-doped TBZ glass has a lesser bandgap than that of Er-doped glass.