The Ni-related centers in synthetic crystals were studied by using optical and spin resonance methods. The 0/- re-charging level of Nis was found to be at 2.47eV below the conduction band. A study of the Ni-related 1.4eV system, by means of temperature-dependent luminescence and absorption methods, exhibited an unusual behavior at temperatures below 25K. This was explained in terms of re-absorption processes.

D.M.Hofmann, P.Christmann, D.Volm, K.Pressel, L.Pereira, L.Santos, E.Pereira: Materials Science Forum, 1995, 196-201, 79-84