Study of visible, NIR, and MIR spectroscopic properties of Er³⁺-doped tellurite glasses and glass–ceramics

In this paper, the structural, thermal, optical, and spectroscopic properties of Er³⁺-doped tellurite glasses with the composition 68.25TeO₂–19.5ZnO–9.75X–2.5Er₂O₃ (in mol%) with X = BaO, Na₂O, and Bi₂O₃ are reported. The glasses were prepared using the standard melt quenching method. The investigated glasses exhibit low phonon energy (∼745 cm⁻¹) and low glass transition temperature varying between 300 and 350°C depending on the glass composition. The Raman spectra show a regular tellurite structure with variations in the number of bridging and non-bridging oxygens depending on the glass composition, the Na₂O and Bi₂O₃-containing glasses having the most and the least polymerized network, respectively. A thermal treatment of the glasses leads to the formation of crystals, the composition of which depends on the glass composition, as revealed by X-ray diffraction analysis and confirmed using scanning electron microscope-energy-dispersive spectroscopy. The precipitation of Er-containing crystals in the Na₂O and BaO-containing glasses leads to an increase in the intensity of the upconversion emissions. Although the Er³⁺ ions remain in the amorphous part of the Bi₂O₃-containing glass after heat treatment, it is the precipitation of Bi_3.2Te_0.8O_6.4 crystals in this glass, which is thought to decrease the distance between the Er³⁺ ions leading to an increase in the intensity of the upconversion and mid-infrared emissions.