A comparative photoluminescence study of group-II impurities (Be, Zn, Cd) in O-rich and O-poor material showed that differing host materials led to distinctly different photoluminescence spectra. A detailed study was made of the spectra for Cd-doped material, and it was shown that strong parallels existed between the properties of this material and those of Be-doped and Zn-doped material. Isotope shifts were observed in both zero-phonon lines and in phonon side-bands. This confirmed the involvement of Cd and indicate that, in all of the cases reported here, only one Cd atom was involved in the defects. Uniaxial stress and Zeeman data also confirmed the existence of close parallels between this family of group-II related defects in O-rich material.

S.E.Daly, E.McGlynn, M.O.Henry, J.D.Campion, K.G.McGuigan, M.C.DoCarmo, M.H.Nazare: Materials Science Forum, 1995, 196-201, 1303-8