The optical absorption of substitutional O (OAs) in the near-infrared region was investigated in O-rich samples by measuring the magnetic circular dichroism. A dichroism was discovered which originated from a paramagnetic ground state. By investigating its thermal decay kinetics and its dependence upon optically-induced re-charging processes which involved EL2 defects, and by comparison with analogous local vibrational mode measurements, it was shown that the magnetic circular dichroism was due to the metastable B' charge state of the OAs centers. The B' state was thus identified as being the paramagnetic charge state of the OAs center.

M.Linde, J.M.Spaeth, H.C.Alt: Applied Physics Letters, 1995, 67[5], 662-4