The effect of BaF₂, MgF₂, and AlF₃ on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]₄ and [GeO]₆ units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF₂. The ²⁷Al MAS NMR spectrum of BGG glass with AlF₃ suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions increases in the BGG + MgF₂ glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties.

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 ^[4]Ge to ^[6]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.

This work reports on the fabrication and analysis of near-infrared and mid-infrared luminescence spectra and their decays in fluoroindate glasses co-doped with Yb³⁺/Ho³⁺. The attention has been paid to the analysis of the Yb³⁺→ Ho³⁺ energy transfer processed ions in fluoroindate glasses pumped by 976 nm laser diode. The most effective sensitization for 2 μm luminescence has been obtained in glass co-doped with 0.8YbF₃/1.6HoF₃. Further study in the mid-infrared spectral range (2.85 μm) showed that the maximum emission intensity has been obtained in fluoroindate glass co-doped with 0.1YbF₃/1.4HoF₃. The obtained efficiency of Yb³⁺→ Ho³⁺ energy transfer was calculated to be up to 61% (0.8YbF₃/1.6HoF₃), which confirms the possibility of obtaining an efficient glass or glass fiber infrared source for a MID-infrared (MID-IR) sensing application.

An investigation of fluoroindate glass and fiber co-doped with Yb³⁺/Er³⁺ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs—²H_11/2 and ⁴S_3/2), non-thermally coupled levels (non-TCLs—⁴F_7/2 and ⁴F_9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K⁻¹—glass, 0.0019 K⁻¹—glass fiber ²H_11/2 → ⁴S_3/2 transition) and relative sensitivity (2.05% K⁻¹—glass, 1.64% K⁻¹—glass fiber ⁴F_7/2 → ⁴F_9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications.