Jahn-Teller vibronic coupling in II-VI compounds with Cr2+ ion

A theoretical study of the vibronic Jahn-Teller interaction in a series of II-VI crystals doped with Cr2+ ion is reported. The vibronic coupling parameters for the tetrahedrally coordinated Cr2+ ion (high-spin d4 configuration) are evaluated in the framework of the exchange charge model of the crystal field accounting for the exchange and covalence effects. The calculations demonstrate the leading role of the trigonal vibrations for the 5T2 term although the contribution of tetragonal modes is also important; the full symmetric and tetragonal vibrations for the 5E term significantly contribute to the phonon broadening of the absorption and emission bands related to the 5E ↔ 5T2 transition in Cr2+ ion.