Structural origin of spectral broadening of 1.5-μm emission inEr3+-doped tellurite glasses

The emission spectra and the lifetimes of the lasing transition ${}^4{I}_{13/2}{-}^4{I}_{15/2}$ in ${\mathrm{Er}}^{3+}$-doped ${\mathrm{TeO}}_2{-\mathrm{Z}\mathrm{n}\mathrm{O}-\mathrm{N}\mathrm{a}}_2\mathrm{O}$ ternary glasses have been studied. The investigation includes two main studies: The first part discusses the Raman spectroscopic analysis of the host glass structure. In the second part, we explain the dependence of ${\mathrm{Er}}^{3+}$-ion photoluminescence near 1500 nm on ${\mathrm{OH}}^{\mathrm{-}}$-ion concentration. The influence of the concentrations of ${\mathrm{Er}}_2{\mathrm{O}}_3$ and the glass structure modifiers (ZnO, ${\mathrm{Na}}_2\mathrm{O})$ on the lifetimes of ${}^4{I}_{13/2}$ level and line shape of the emission spectra has been analyzed. It was observed that the increasing concentrations of ${\mathrm{Er}}^{3+}$ ions resulted in spectral broadening as a consequence of ${\mathrm{Er}}^{3+}$ being distributed in the glass structure. The measured lifetimes of ${}^4{I}_{13/2}$ emission vary between 4.5 and 7.8 ms and strongly depend on OH-ion concentrations. The structural origin of the spectral broadening of the Er emission line is particularly discussed by analyzing the spectral components in the tellurite, modified silicate, and fluoride glass hosts. The number of spectral components at room temperature in Er-doped ${\mathrm{TeO}}_2,$ silicate, and fluoride glasses are compared, and the dependence of line strengths and site-to-site variation of the rare-earth ions on the structure of each glass is also explained. The unusually large broadening of the ${\mathrm{OH}}^{\mathrm{-}}$ band in the ${\mathrm{TeO}}_2$ family of glasses is analyzed in the context of the tellurite glass structure.