The 4T1(F)-to-4A2(F) transition of Co2+ (d7) ions was detected by its emission at about 4K. A no-phonon line at 5558/cm was shown to coincide with the inverse absorption transition. The luminescence revealed a moderate coupling to lattice vibrations. An exponential decay, with a time-constant of 0.0001s, was detected. A rich fine-structure was exhibited by the 4A2(F)-to-4T1(P) absorption. It could be qualitatively described in terms of spin-orbit and Jahn-Teller interactions. The properties of 2 additional emission bands which were found between 4200 and 5600/cm were investigated. One of them was dominated by a no-phonon line at 5471/cm. The capture of a hole by a neutral donor was suggested to be a possible explanation for a broad luminescence band which peaked near to 4600/cm.

G.Goetz, H.J.Schulz: Physica Status Solidi B, 1992, 169[1] 217-24