Optical constants of Tl4Ga3InSe8 layered single crystals

The optical properties of Tl4Ga3InSe8 layered single crystals have been studied by means of transmission and reflection measurements in the wavelength range of 500-1100 nm. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.94 and 2.20 eV, respectively. Transmission measurements carried out in the temperature range of 10-300 K revealed that the rate of change of the indirect band gap with temperature is γ=−4.1×10−4 eV/K. The absolute zero value of the band gap energy was obtained as Egi(0)=2.03 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index were found to be 4.10 eV, 23.17 eV, 6.21×1013 m−2 and 2.58, respectively. From X-ray powder diffraction study, the parameters of monoclinic unit cell were determined.