Refractive index change dependence on Ge(1) defects in {gamma}-irradiated Ge-doped silica

We present an experimental study regarding the effects of the {gamma} radiation on silica glass doped with Ge up to 10 000 ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changes in the refractive index ({delta}n) as a function of the oxygen deficiency of the samples, evaluated from the ratio between the germanium lone pair centers (GLPC) and the Ge content. {delta}n at 1500 nm have been estimated using optical-absorption spectra in the range 1.5-6 eV. We have found that {delta}n is independent of Ge differences for GLPC/Ge values <10{sup -4}, while it depends on Ge for larger oxygen deficiencies. In details, the oxygen deficiency can reduce the induced {delta}n of the investigated materials and our studies evidence that the photosensitivity of the GeO{sub 2}-SiO{sub 2} glass is reduced until the GLPC concentration reaches values of 2x10{sup 17}-5x10{sup 17} defects/cm{sup 3}. We have also investigated the induced concentration of paramagnetic point defects [Ge(1), Ge(2), and E'Ge] using the electron-paramagnetic-resonance (EPR) technique. From the comparison of the optical and EPR data we have further found a relation between the induced optical-absorption coefficient at 5.8 eV and Ge(1) defects, a linear correlation between Ge(1) and {delta}n and themore » absence of a correlation between the other paramagnetic defects and {delta}n. These findings suggest that the {delta}n phenomenology is closely related to the Ge(1) generation mechanisms and this latter is affected by the oxygen defic0011ien.« less