Microstructural changes in glasses (5 or 13mol%GeO2) which had been irradiated with 5 or 6.4eV light were investigated by means of Raman spectroscopy. The low-frequency so-called boson bands at 50/cm, in both samples, shifted upwards during irradiation, but their intensities exhibited opposite changes. This indicated that the thermal damage to the surface, caused by energetic ultra-violet photons, was related to the Ge content of the glass. The intensities of the D1 and D2 defect lines increased and shifted to higher frequencies; thus reflecting a reduction in the Si-O-Si bond angle during irradiation. This was suggested to be due to a change, in ring statistics, in favor of smaller rings. That is, 6-fold rings transformed to 3-fold and 4-fold rings during ultra-violet irradiation. The opposite changes in intensity of the defect lines were attributed to variations in the network structure.

F.X.Liu, J.Y.Qian, X.L.Wang, L.Liu, H.Ming: Physical Review B, 1997, 56[6], 3066-71