First-principles configuration interaction calculations were made of the optical transitions of the E' center. This was a hole which was trapped at an O vacancy, (-O)3Si•+Si(O-)3, in silica. Two competing excitation mechanisms were found. These were the promotion of an electron from an O(2p) valence band orbital into the singly-occupied Si dangling bond, and charge-transfer transitions from (-O)3Si• to +Si(O-)3. The 2 excitations occurred at similar energies, (about 5.9eV), but only the charge-transfer process had a high intensity. The excitation was followed by a complex non-radiative decay process. This was suggested to explain the absence of luminescence from this center.

G.Pacchioni, G.Ieranò, A.M.Márquez: Physical Review Letters, 1998, 81[2], 377-80