The electronic absorption of EL2 centers was shown to be related to the electron and hole photo-ionizations, and to a transition from its ground state to a metastable state. Under illumination with photon energies in the near-infrared region, these 3 processes, with different optical cross-sections, exhibited differing kinetics as a function of the illumination time. It was recalled that it had been shown that the photosensitivity (under 1.25eV illumination) of the local vibrational mode absorption that was induced by some deep defect centers in semi-insulating material was a result of the electron and hole photo-ionizations of EL2. Direct measurements were made here of the kinetics of the electronic transition that was associated with EL2 under 1.25eV illumination. These supported the expected charge transfer among various charge states of the EL2 center. A prediction that was based upon a simple rate equation model was found to be in good agreement with the experimental data.

W.K.Ge, C.Y.Song, D.S.Jiang: Physical Review B, 1996, 53[15], 9809-13