Impurity optical absorption of Co2+-doped MgAl2S4 and CaAl2S4 single crystals

Abstract

MgAl2S4, CaAl2S4, MgAl2S4:Co2+, and CaAl2S4:Co2+ single crystals were grown by the chemical transport reaction method. The single crystals crystallized into an orthorhombic structure. Optical energy gaps of the MgAl2S4, CaAl2S4, MgAl2S4:Co2+, and CaAl2S4:Co2+ single crystals at 13K were found to be 4.334, 4.835, 3.732, and 4.092eV, respectively. Impurity optical absorption peaks were observed in the MgAl2S4:Co2+ and CaAl2S4:Co2+ single crystals. The impurity absorption peaks are thought to originate in electron transitions between energy levels of Co2+ ions sited in Td symmetry in the MgAl2S4:Co2+ and CaAl2S4:Co2+ single crystals.