| Summary: | This study presented an analysis of the TeO<sub>2</sub>/GeO<sub>2</sub> molar ratio in an oxide glass system. A family of melt-quenched glasses with the range of 0–35 mol% of GeO<sub>2</sub> has been characterized by using DSC, Raman, MIR, refractive index, PLE, PL spectra, and time-resolved spectral measurements. The increase in the content of germanium oxide caused an increase in the transition temperature but a decrease in the refractive index. The photoluminescence spectra of europium ions were examined under the excitation of 465 nm, corresponding to <sup>7</sup>F<sub>0</sub> → <sup>5</sup>D<sub>2</sub> transition. The PSB (phonon sidebands) analysis was carried out to determine the phonon energy of the glass hosts. It was reported that the red (<sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>2</sub>) to orange (<sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>1</sub>) fluorescence intensity ratio for Eu<sup>3+</sup> ions decreased from 4.49 (Te0Ge) to 3.33 (Te15Ge) and showed a constant increase from 4.58 (Te20Ge) to 4.88 (Te35Ge). These optical features were explained in structural studies, especially changes in the coordination of <sup>[4]</sup>Ge to <sup>[6]</sup>Ge. The most extended lifetime was reported for the Eu<sup>3+</sup> doped glass with the highest content of GeO<sub>2</sub>. This glass was successfully used for the drawing of optical fiber.
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