Comparative first-principles analysis of crystal field splitting, charge transfer energies and covalent effects for Cr ²⁺ and Fe ²⁺ ions in II-VI and III-V compounds

Detailed comparative first-principles study of crystal field splitting, covalent effects and "ligand-metal" charge transfer (CT) energies in ZnS, ZnSe, ZnTe, and CdTe crystals doped with Cr ²⁺ and Fe ²⁺ ions and GaAs, GaP, and InP crystals doped with Fe ²⁺ ions is reported. It is shown that the contribution of ligands to the 3d orbitals of central ion is greater in case of Fe ²⁺ ion. As a consequence, CT energies in the Fe ²⁺ -doped crystals are lower than in the Cr ²⁺-doped ones. In addition, theoretical absorption spectra were calculated and compared with experimental data.