This study presented an analysis of the TeO2/GeO2 molar ratio in an oxide glass system. A family of melt-quenched glasses with the range of 0–35 mol% of GeO2 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 7F0 → 5D2 transition. The PSB (phonon sidebands) analysis was carried out to determine the phonon energy of the glass hosts. It was reported that the red (5D0 → 7F2) to orange (5D0 → 7F1) fluorescence intensity ratio for Eu3+ 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 Ge to Ge. The most extended lifetime was reported for the Eu3+ doped glass with the highest content of GeO2. This glass was successfully used for the drawing of optical fiber.
A series of lithium-germanate glasses with different manganese concentration is synthesized. Li2Ge7O15 nanocrystals nucleate in the glass matrix via standard volume crystallization technique thus obtaining lithium-germanate glass-ceramics. The glass-ceramics possess intense emission near 660-670 nm under two-band excitation at 330 and 450 nm. The luminescence lifetime is 550 μs for 0.05 mol.% MnO2-doped glass-ceramics. The glass-ceramics obtained can be used as a source of deep-red radiation.