Effects of GeO2 concentration on the absorption and fluorescence behaviors of Yb3+ in tellurite glasses

Yb3+-doped tellurite glasses exhibited largest absorption and emission cross sections. However, it is more valuable to achieve larger Stark splitting of Yb3+ than improve the absorption and emission cross sections. In this work, we introduced a part of GeO2 into tellurite glass matrix to enlarge the Stark splitting of Yb3+. The effects of GeO2 concentration on the spectroscopic characteristic of Yb3+ were systematically investigated. The stimulated absorption and emission cross sections increased to be 1.62 pm2 and 0.88 pm2 when the GeO2 concentration up to 30 mol%, then decreased with the GeO2 concentration further increased. The Stark splitting of Yb3+ do not change until the GeO2 concentration up to 30 mol%. The NIR fluorescence lifetimes of Yb3+ drastically decreased from 850 μs to 385 μs with the GeO2 concentration increasing, which was due to the increasing multi-phonon relaxation rate and reabsorption. Intense NIR fluorescence were observed when excited by the ultraviolet light, which can be ascribed to the energy transfer from the CTB of Yb3+-O2- couple to Yb3+. The CTB showed a slight blue-shift from 338 to 313 nm with GeO2 concentration increasing, which was ascribed to the size of the cation site would increase.