Temperature- and excitation-dependent photoluminescence in TlGaSeS layered crystals

Photoluminescence (PL) spectra of TlGaSeS layered single crystals have been studied in the wavelength region of 695–1010 nm and in the temperature range of 20–56 K. Two PL bands centered at 773 (1.605 eV, A-band) and 989 nm (1.254 eV, B-band) were observed at T = 20 K. Variations of both bands have been investigated as a function of excitation laser intensity in the range from 4.2 to 111.4 mW cm−2. These bands are attributed to recombination of charge carriers through donor–acceptor pairs located in the band gap of the crystal. Radiative transitions from deep donor levels located at 0.721 and 1.069 eV below the bottom of conduction band to shallow acceptor levels located at 0.008 and 0.011 eV above the top of the valence band are suggested to be responsible for the observed A- and B-bands in the PL spectra, respectively.

Research highlights▶ PL spectra of TlGaSeS layered single crystals have been studied in the wavelength region of 695–1010 nm and in the temperature range of 20–56 K at different excitation laser intensities in the range from 4.2 to 111.4 mW cm−2. ▶ The variation of the spectra with laser excitation intensity and temperature suggest that the transitions between the donor and acceptor levels can be responsible for the observed emission bands.