Thermal and optical properties of Tm³⁺ doped tellurite glasses

Ultraviolet, visible (UV/VIS) and differential thermal analysis (DTA) measurements were carried out in order to investigate the optical and thermal properties of various 0.5 mol.% Tm₂O₃ containing (1 - x)TeO₂ + xLiCl glasses in molar ratio. The samples were prepared by fusing the mixture of their respective reagent grade powders in a platinum cricuble at 750°C for 30 min. DTA curves taken in the 23-600°C temperature range with a heating rate of 10°C/min reveal a change in the value of the glass transition temperature, T_g, while melting was not observed for the glasses containing LiCl content less than 50 mol.%. These glasses were found to be moisture-resistant. However, the glasses with LiCl content higher than 50 mol.%, in which a melting peak was observed at T_c = 401°C, were moisture-sensitive. Absorption measurements in the UV/VIS region of the glasses without Tm₂O₃ content show that the Urbach cutoff occurs at about 320 nm and, is relatively independent of the LiCl content. Six absorption bands were observed in the Tm₂O₃ doped glasses corresponding to the absorption of the ¹G₄, ³F₂, ³F₃ and ³F₄, ³H₅ and ³H₄ levels from the ³H₆ ground level of Tm³⁺ ions. The spectra also show that the integrated absorption cross-section of each band depends on the glass composition. Judd-Ofelt theory was used to determine the Judd-Ofelt parameters as well as the radiative transition probabilities for the metastable levels of Tm³⁺ ions in (0.3)LiCl + (0.7) TeO₂: 0.01 Tm₂O₃ glass which is moisture-resistant.