Thermal analysis and linear optical properties of (1−x)TeO2-(x)ZnCl2 optical glasses for photonic applications

The investigation covers the thermal and linear optical properties of binary TeO₂-ZnCl₂ optical glass systems contain different ZnCl₂ compositions ranging from 10 to 40mol%. Preparation of the glass systems were realized by melting the mixture of TeO₂ and ZnCl₂ chemicals in a platinum crucible at 850°C for 60 min in air. In the experiments, thermal analysis was performed to determine the thermal characteristics such as, glass transition (T_g), crystallization (T_p), and melting (T_m) temperatures for different heating rates (B=10, 20, 30 and 40 °C/min) by using the differential thermal analysis (DTA) plot. By considering the DTA plots, the crystallization activation energies were determined by using the Ozawa and modified Kissinger equations. Finally, thermal analysis show that the crystallization activation energies were 487.6kJ/mol, 215.8kJ/mol, 392.kJ/mol, and 273.3kJ/mol for the x=10, 20, 30, and 40mol% ZnCl₂ contents, respectively. Optical band gaps (direct and indirect) and Urbach energies of the glass samples were estimated from the absorption spectra measured between 300 and 800nm. The direct band gap energies decrease from 3.65 eV to 3.35 eV, and indirect band gap energies also decrease from 3.59 eV to 3.30 eV by increasing the ZnCl₂ content from 10 to 40 mol%, respectively.