Low-temperature visible photoluminescence and optical absorption in Tl2In2Se3S semiconductor

The emission band spectra of undoped Tl2In2Se3S layered crystals have been studied in the temperature range of 25-63 K and the wavelength region of 570-700 nm. A broad photoluminescence band centered at 633 nm (1.96 eV) was observed at T=25 K. Variation of emission band has been studied as a function of excitation laser intensity in the 2.7-111.4 mW cm−2 range. Radiative transitions from shallow donor level located at 0.03 eV below the bottom of conduction band to deep acceptor level located at 0.23 eV above the top of the valence band were suggested to be responsible for the observed PL band. From X-ray powder diffraction and optical absorption study, the parameters of monoclinic unit cell and the energy of indirect band gap were determined, respectively.