Low-temperature visible photoluminescence spectra of Tl2GaInSe4 layered crystals
The photoluminescence (PL) spectra of Tl2GaInSe4 layered single crystals has been investigated in the 10-95 K temperature, 0.04-3.98 W cm-2 excitation laser intensity and 1.75-2.07 eV energy ranges. We have observed an emission band located at 1.912 eV (648 nm) at 10 K for an excitation intensity of 1.40 W cm-2. The band had a half-width of 0.105 eV and an asymmetric Gaussian line shape. It has been found to red-shift with increasing temperature or decreasing excitation intensity. To explain the observed PL behaviour, we propose that the emission is due to the radiative recombination of a donor-acceptor pair (DAP) with an electron occupying a donor level located at 0.355 eV below the conduction band and a hole occupying an acceptor level located at 0.036 eV above the valance band. The blue-shift of the peak energy and the sub-linear increase of the band intensity for the observed emission band with increasing excitation intensity is explained using the in-homogeneously spaced DAP recombination model.