Concentration effects in the photoluminescence spectra of ZnAl2(1âˆ’Ñ )Cr2xS4

The luminescence properties of the ZnAl2(1−х)Cr2хS4 single crystals with different chromium content are investigated. The emission spectra of the samples with a small amount of chromium (х ⩽ 0.005) consist of the R-line (ER = 1.61 eV) and its phonon side band. At increasing of chromium concentration two new U-bands centered at ЕU(a) = 1.45 eV and ЕU(b) = 1.3 eV appear in the emission spectra. It is assumed, that the increase of the new broad bands intensity with increasing of chromium concentration takes place due to the formation of nonequivalent Cr+3-ions occupying octahedral sites, in the first cationic coordination sphere of which one or two aluminum ions are replaced by chromium ions.