COMPUTER MODELING OF THE OPTICAL-PROPERTIES OF SUBSTITUTIONAL CHROMIUM IMPURITIES IN HALIDE ELPASOLITES

Ah initio embedded-cluster molecular-orbital calculations were performed with the MELD program on both ground (4A2g) and excited (4T2g) electronic states of substitutional Cr3+ in the halide elpasolites K2NaGaF6, K2NaScF6 and Cs2NaYCl6. External interactions of the molecular cluster were represented by pair potentials, and lattice relaxation was accomplished by means of a modification of the HADES lattice-statics program. The calculations account successfully for the pressure dependence of photoluminescence spectra and of vibration frequencies inferred from their vibronic structure.