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Tellurite glasses have garnered considerable interest as optical host materials due to their advantageous properties, including low processing temperature, high resistance to corrosion and crystallization, and excellent solubility for rare earth ions. However, their applicability in the infrared (IR) region is limited by the absorption of species with distinct vibrations. The incorporation of fluorides has emerged as a promising approach to reduce hydroxyl (OH) absorption during the precursor melting process. In this study, we investigated the influence of ZnF 2 on a glass matrix composed of TeO 2 -ZnO-Na 2 O, resulting in notable changes in the glass structure and optical properties, with Eu 3+ serving as an environmental optical probe. The samples underwent comprehensive structural, thermal, and optical characterization. Structural analyses encompassed 19 F and 125 Te nuclear magnetic resonance (NMR), with the latter being complemented by mathematical simulations, and these findings were consistent with observations from Raman scattering. The main findings indicate an enhancement in thermal stability, modifications in the Te-O connectivity, and a reduction in emission intensity attributed to the effects of ligand polarizability and symmetry changes around Eu 3+ . Additionally, the fluorotellurite matrices exhibited a shift in the absorption edge toward higher energies, accompanied by a decrease in mid-IR absorptions, thereby expanding the transparency window. As a result, these glass matrices hold substantial potential for applications across various regions of the electromagnetic spectrum, including optical fiber drawing and the development of solid-state emitting materials., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

While phosphotellurite glasses have superior properties over SiO 2 -based glasses for many applications in optoelectronics and photonic devices, their high hydroxyl content limits their use in the mid-infrared range. This drawback can be overcome by fluoride addition to the formulation. In this work, we report the preparation, optical, and structural characterization of new glasses in the ternary system TeO 2 - x NaF-NaPO 3 having the compositions 0.8TeO 2 -0.2[ x NaF-(1 - x )NaPO 3 ] and 0.6TeO 2 -0.4[ x NaF-(1 - x )NaPO 3 ] (0 ≤ x ≤ 1) obtained by the traditional melt-quenching method and labeled as T8NN x and T6NN x , respectively. Differential scanning calorimetry (DSC) reveals high thermal stability against crystallization, with T x - T g varying from 80 to 130 °C, depending on fluoride/phosphate ratios. Raman spectroscopy suggests that the network connectivity increases with increasing phosphate concentration. 125 Te, 23 Na, 31 P, and 19 F NMR spectroscopy provides detailed structural information about Te-O-P, Te-F, Te-O-Te, P-O-P, and P-F linkages and the charge compensation mechanism for the sodium ions. The present study is the first comprehensive structural characterization of a fluorophosphotellurite glass system.