Effects of GeO2 on the thermal stability and optical properties of Er3+/Yb3+-codoped oxyfluoride tellurite glasses

The aim of this article was to study the influence of GeO2 on the thermal stability and optical properties of Er3+/Yb3+ codoped (70 − x)TeO2–xGeO2–PbF2–BaF2 (TGEYx) glasses prepared by using a melting method. The properties of Er3+/Yb3+ codoped glasses were investigated by using differential scanning calorimetry, upconversion luminescence, Raman and optical absorption spectra. The results indicated that TGEY35 glass with the germanate–tellurite mixed network showed the best thermal stability and poor crystallization tendency. With increasing the GeO2 content, the maximum phonon energy of oxyfluoride tellurite glass network increased, while the phonon density decreased. The upconversion emission intensities enhanced obviously based on the decreasing phonon density of glass hosts, while the increasing red emission (657 nm) with the increase of GeO2 concentration was attributed to the relative larger maximum phonon energy which matching the energy gap between the pertinent 4S3/2 and 4F9/2 levels.