Optical properties of undoped, Co 2+- and Er 3+-doped CdAl 2Se 4 single crystals

Abstract

Single crystals of CdAl 2Se 4, CdAl 2Se 4:Co 2+ and CdAl 2Se 4:Er 3+ were grown by the chemical transport reaction method using iodine as a transporting material. The crystal structure of these single crystals has been shown to be a defect chalcopyrite, and the direct bandgap at 10 K has been found to be 3.082 eV for CdAl 2Se 4, 2.683 eV for CdAl 2Se 4:Co 2+ and 2.980 eV for CdAl 2Se 4:Er 3+, respectively. We observed impurity optical absorption peaks due to electron transitions between the energy levels of Co 2+ ions sited at T d symmetry of the host material. We also observed two broad blue-green photoluminescence peaks centered at 458 and 539 nm in the photoluminescence spectrum at 10 K of CdAl 2Se 4 single crystals. For CdAl 2Se 4:Er 3+ single crystals, on the other hand, sharp photoluminescence peaks were observed, which are due to emission transitions between the energy levels of Er 3+ ions with T d symmetry sites.