Photo-induced phenomena in GeO2 glass

Photo-induced changes in GeO2 glass have been studied in terms of its optical and structural properties. Band-gap excitation gives rise to modifications in mid-gap optical absorption and photo-luminescence spectra. It also produces electron-spin signals at g 1.995 and 2.008. Raman-scattering spectrum becomes sharper, X-ray diffraction patterns show a disappearance of a crystalline peak, and the illuminated surfaces expand. These observations can be accounted for by assuming bond transformations from rutile-like to defective quartz-like structures and/or from small to large rings. These photo-induced changes in GeO2 are discussed in comparison with those in SiO2 and GeS2.