Photoluminescence spectra of Zn1-xCdxAl2Se4 single crystals

We investigated the photoluminescence spectra as well as the crystal struct ure and optical energy gaps of the Zn1-xCdxAl2Se4 single crystals grown by the chemical transport reaction method. It was shown from the analysis of t he observed x-ray diffraction patterns that these crystals have a defect ch alcopyrite structure for a whole composition. The lattice constant cr incre ases from 5.5561 A for x = 0.0 (ZnAl2Se4) to 5.6361 A for x = 1.0 (CdAl2Se4 ) with increasing x, whereas the lattice constant c decreases from 10.8890 A for x = 0.0 to 10.7194 A for x = 1.0. The optical energy gaps at 13 K wer e found to range from 3.082 eV (x = 1.0) to 3.525 eV (x = 0.0). The tempera ture dependence of the optical energy gaps was well fitted with the Varshni equation. We observed two emission bands consisting of a strong blue emiss ion band and a weak broad emission band due to donor-acceptor pair recombin ation in the Zn1-xCdxAl2Se4 for 0.0 less than or equal to x less than or eq ual to 1.0. These emission bands showed a red shift with increasing x. The energy band scheme for the radiative mechanism of the Zn1-xCdxAl2Se4 was pr oposed on the basis of the photoluminescence thermal quenching analysis alo ng with the measurements of photo-induced current transient spectroscopy. T he proposed energy band model permits us to assign the observed emission ba nds.