Tuning Optical Absorption Edge by Composition and Temperature in $TlGaS_{2x}Se_{2(1-x)}$ Layered Mixed Crystals (0 ≤ x ≤ 1)

Optical properties of $TlGaS_{2x}Se_{2(1-x)}$ mixed crystals (0 ≤ x ≤1) have been studied using the transmission and reflection measurements in the wavelength range of 400-1100 nm. The optical indirect band gap energies were determined through the analysis of the absorption data. It was found that the energy band gaps increase with increase of sulfur atoms content in $TlGaS_{2x}Se_{2(1-x)}$ mixed crystals. From the transmission measurements carried out in the temperature range of 10-300 K, the rates of change of the indirect band gaps with temperature were established for the different compositions of mixed crystals studied.