The magneto-optical properties of transition metal defects were investigated. A structured luminescence band, with its zero-phonon line at 1.1934eV and a comparatively weak but richly-structured phonon side-band, was attributed to the 1E(D)-3A2(F) transition of a d2-configuration (on the basis of the observed Zeeman behavior). The luminescence lifetime of 65s indicated strong mixing with the 3A2(F) multiplet. The observation of intra-center excitation bands in n-type material strongly suggested that Ti2+ was a luminescence center. The characteristic ground-state splitting of a second near-infrared luminescence, with its zero-phonon line at 1.2988eV, could be unambiguously attributed to Fe3+.

R.Heitz, P.Thurian, I.Loa, L.Eckey, A.Hoffmann, I.Broser, K.Pressel, B.K.Meyer, E.N.Mokhov: Materials Science Forum, 1995, 196-201, 719-24