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

Abstract

<p>In this paper, the structural, thermal, optical, and spectroscopic properties of Er<sup>3+</sup>-doped tellurite glasses with the composition 68.25TeO<sub>2</sub>–19.5ZnO–9.75X–2.5Er<sub>2</sub>O<sub>3</sub> (in mol%) with X = BaO, Na<sub>2</sub>O, and Bi<sub>2</sub>O<sub>3</sub> are reported. The glasses were prepared using the standard melt quenching method. The investigated glasses exhibit low phonon energy (∼745 cm<sup>−1</sup>) 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 Na<sub>2</sub>O and Bi<sub>2</sub>O<sub>3</sub>-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 Na<sub>2</sub>O and BaO-containing glasses leads to an increase in the intensity of the upconversion emissions. Although the Er<sup>3+</sup> ions remain in the amorphous part of the Bi<sub>2</sub>O<sub>3</sub>-containing glass after heat treatment, it is the precipitation of Bi<sub>3.2</sub>Te<sub>0.8</sub>O<sub>6.4</sub> crystals in this glass, which is thought to decrease the distance between the Er<sup>3+</sup> ions leading to an increase in the intensity of the upconversion and mid-infrared emissions.</p>