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-ZnAl₂S ₄: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.