Photoluminescence Studies of Wurtzite Type W-ZnAl2S4 Single Crystals.

Single crystals of wurtzite-type W-ZnAl2S4 have been grown by the chemical vapor transport technique. Structural studies of the obtained crystals using powder X-ray diffraction analysis revealed their wurtzite structure with random distribution of cations at tetrahedral sites, whereas optical experiments showed that the crystals obtained had a direct band gap of ~3.7 eV and exhibited a strong blue photoluminescence (PL) even at room temperature, with two different luminescence peaks, each of which had a different excitation band. In order to explain the PL results, the configuration coordinate model for the radiative transitions involved in the formation of the PL bands has been proposed. The model takes into account a lattice relaxation around the deep center responsible for the blue emissions, as well as the splitting of the valence band of W-ZnAl2S4 caused by the effect of the noncubic crystal field and spin-orbit interaction.