The formation of paramagnetic centers in glasses, by irradiation with 5eV KrF excimer-laser pulses, was investigated at 77K by using electron-spin resonance. The essential photochemical reaction was the generation of electron-trapped centers which were associated with 4-fold coordinated Ge ion and self-trapped hole centers of bridging O. This reaction proceeded by band-to-band excitation via a 2-photon absorption process. Part of the coordinated Ge ion was converted to the GeE' center during prolonged irradiation at 77K. The differences between the electron spin resonance spectra, before and after annealing at room temperature, revealed that most self-trapped hole centers disappeared by recombination with coordinated Ge ions during annealing at room temperature. The predominant paramagnetic centers which remained after annealing were coordinated Ge ions and GeE', and their total concentration was approximately half of that before annealing. The close relationship between the generation of paramagnetic centers and the decay of emission due to Ge2+ suggested that the hole transfer from self-trapped hole centers to Ge2+ was followed by their structural relaxation.

Pair Generation of Ge Electron Centers and Self-Trapped Hole Centers in GeO2-SiO2 Glasses by KrF Excimer-Laser Irradiation. J.Nishii, K.Kintaka, H.Hosono, H.Kawazoe, M.Kato, K.Muta: Physical Review B, 1999, 60[10], 7166-9