Comparative first-principles analysis of undoped and Co2+-doped α-ZnAl2S4

The experimental and theoretical studies of the optical properties of pure α-ZnAl2S4 and α-ZnAl2S4:Co2+ crystals were carried out. The ab initio and crystal field calculations of the structural and optical properties of α-ZnAl2S4:Co2+ were compared with the corresponding experimental data. It was shown that the lowest cobalt 3d states are located at about 0.5 eV above the valence band’s top. The complete energy level scheme of the α-ZnAl2S4:Co2+ system, which includes the host’s electronic band structure and impurity ion’s energy levels, was suggested on the basis of the performed calculations.

► Structural, electronic, and optical properties of α-ZnAl2S4:Co2+ were calculated.
► Ab initio and crystal field methods were used in all calculations.
► Position of the Co2+ energy levels in the host band gap was estimated.