Absorption and luminescence of Cr2+(d4) in II-VI compounds

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Abstract
Infrared absorption and luminescence measurements of substitutional Cr2+(d4) in the II-VI compounds ZnS, ZnSe, ZnTe and CdTe are reported. The experimental results are interpreted in the framework of crystal field theory with spin-orbit coupling and a substantial Jahn-Teller interaction in the 5T2 ground state and a much smaller, but significant, Jahn-Teller interaction in the excited 5E state. With a semiclassical model and a Monte Carlo computing technique convoluted shapes of absorption and luminescence spectra are obtained. The Jahn-Teller energy for the 5T2 ground state is found to be approximately 350 cm-1. For the first time a Jahn-Teller energy for the excited 5E state is reported, and has a value of approximately 50 cm-1. The inclusion of ligand field effects in the spin-orbit coupling constant was found to be important.