The Ge-E’ centers generated by ultra-violet irradiation of Ge-doped amorphous SiO2 were considered to be closely related to photo-induced refractive-index changes in this material. The structural stability of a Ge-related O deficient center was examined by using the first-principles pseudopotential method. It was found that the puckered configuration with an unpaired paradiamagnetic electron was more stable than the dimer one for a positively charged state. The results provided strong theoretical support for a model of photo-induced transformation of the neutral Ge-related O deficient center into the Ge-E’ center; as proposed for α-quartz and a-SiO2.

E’ Center in Ge-Doped SiO2 Glass. T.Tamura, G.H.Lu, M.Kohyama, R.Yamamoto: Physical Review B, 2004, 70[15], 153201 (4pp)