Fig. 1. Differential thermal analysis curve and Raman spectrum of tellurite-germanate glass undoped with rare earth ions. (a) Differential thermal analysis curve and picture of glass sample; (b) Raman spectrum

Fig. 2. Absorption spectra of rare earth ions doped tellurite-germanate glass. (a) Absorption spectra of Tm₂O₃ doped glass samples; (b) absorption spectra of glass samples doped with Ho³⁺/Yb³⁺, Yb³⁺, and Ho³⁺, respectively

Fig. 3. Fluorescence spectra and decay lifetime curves of rare earth ions doped tellurite-germanate glass. (a) Fluorescence spectra of Tm₂O₃ doped glass samples; (b) fluorescence spectra of Ho³⁺/Yb³⁺ co-doped glass samples; (c) decay life curve of glass sample doped with 0.4% Tm³⁺; (d) decay life curve of glass sample doped with 1% Ho³⁺ and 0.5% Yb³⁺

Fig. 4. Simplified energy level diagrams of Tm³⁺ and Ho³⁺ ions. (a) Tm³⁺ ion; (b) Ho³⁺/Yb³⁺ ions

Fig. 5. Absorption and emission cross sections and gain coefficient of rare earth ions doped tellurite-germanate glass. (a) Absorption and emission cross sections of glass sample doped with 0.4% Tm³⁺; (b) absorption and emission cross sections of glass sample doped with 1% Ho³⁺/0.5% Yb³⁺; (c) gain coefficient of glass sample doped with 0.4% Tm³⁺; (d) gain coefficient of glass sample doped with 1% Ho³⁺/0.5% Yb³⁺