Thermal properties and optical transition probabilities of Tm³⁺ doped TeO₂-WO₃ glass

Glasses with the composition of (1-x)TeO₂+(x)WO₃, where x=0.15, 0.25 and 0.3 were prepared and, their thermal and absorption measurements were carried out. Differential thermal analysis (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 crystallization was not observed for the glasses containing a WO₃ content of more than 15 mol%. All the glasses were found to be moisture-resistant. The absorption bands corresponding to the absorption of the ¹G₄, ³F₂, ³F₃ and ³F₄, ³H₅ and ³H₄ levels from the ³H₆ ground level of the Tm³⁺ ion were observed in the optical absorption spectra. Integrated absorption cross-sections of each band except that of ³H₅ level was found to vary with the glass composition. Judd-Ofelt analysis was carried out for the samples doped with 1.0 mol% Tm₂O₃. The Ω₂ parameter shows the strongest dependence on the host composition and it increases with the increasing WO₃ amount. The value of Ω₄ increases rather slowly while the value of Ω₆ is practically independent of the composition. The strong dependence of the parameter Ω₂ indicates that this parameter is related to the structural change and the symmetry of the local environment of the Tm³⁺ ions in this glass.