Optically detected electron paramagnetic resonance was observed at 36, 67 and 70GHz for all of the absorption bands of this material in the visible spectral range. This demonstrated clearly that the 3 major magnetic circular dichroism features belonged to the same isotropic center. This was a BiGe3+ defect in which the hole was delocalized onto the 4 surrounding O atoms. A simple explanation was provided for an unusual sign of the optically detected electron magnetic resonance, and for a transient behavior of the magnetic circular dichroism at resonance.

B.Briat, H.J.Reyher, A.Hamri, N.G.Romanov, J.C.Launay, F.Ramaz: Journal of Physics - Condensed Matter, 1995, 7[34], 6951-9