Effect of composition on the thermal properties and spontaneous emission probabilities of Tm³⁺-doped TeO₂-LiCl glass

The effect of composition on the thermal properties and the spontaneous emission probabilities of various 0.5 mol% Tm₂O₃ containing (1 - x)TeO₂ + (x)LiCl glasses were investigated using differential thermal analysis (DTA) and ultraviolet-visible-near-infrared (UV/VIS/NIR) absorption measurements. DTA curves of the samples were obtained in the 23-600 °C temperature range with a heating rate of 10 °C/min. The value of the glass transition temperature T_g and the crystallization temperature T_c were found to vary with the glass composition. Melting was not observed for the glasses containing less than 50 mol% LiCl in this temperature range. However, a melting peak was observed at T_m = 401 °C for the glasses having higher than 50 mol% LiCl, which were also found to be moisture-sensitive. Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f-4f transitions of Tm³⁺ ions. Six absorption bands corresponding to the absorption of the ¹G₄, ³F₂, ³F₃, ³F₄, ³H₄, and ³H₄ levels from the ³H₆ ground level were observed. An integrated absorption cross section of each band, except that of ₃H₅ level, was found to vary with the glass composition. The role of the Judd-Ofelt parameters and therefore the effect of the glass composition on the radiative transition probabilities for the metastable levels of Tm³⁺ ions are discussed in detail.