The transfer mechanism between the first excited singlet state and the lowest metastable triplet state of the complex pseudo-donor S-Cu defect was shown to be governed by hyperfine interactions between the electron and the hole which made up the pseudo-donor state and the nuclear spin of the Cu atom which was involved in the defect. It was suggested that this model could explain similar observations in related pseudo-donor type defects.

A.M.Frens, M.E.Braat, J.Schmidt, W.M.Chen, B.Monemar: Physical Review B, 1995, 52[12], 8848-53