Refractive index change dependence on Ge(1) defects in -irradiated Ge-doped silica

We present an experimental study regarding the effects of the gamma radiation on silica glass doped with Ge upto 10 000 ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changesin the refractive index (Dn) as a function of the oxygen deficiency of the samples, evaluated from the ratiobetween the germanium lone pair centers (GLPC) and the Ge content. Dn at 1500 nm have been estimatedusing optical-absorption spectra in the range 1.5–6 eV. We have found that Dn is independent of Ge differencesfor GLPC/Ge values <10^−4, while it depends on Ge for larger oxygen deficiencies. In details, theoxygen deficiency can reduce the induced Dn of the investigated materials and our studies evidence that thephotosensitivity of the GeO2-SiO2 glass is reduced until the GLPC concentration reaches values of2x10^17–5x10^17 defects/cm3. We have also investigated the induced concentration of paramagnetic pointdefects [Ge(1), Ge(2), and E’Ge] using the electron-paramagnetic-resonance (EPR) technique. From the comparisonof the optical and EPR data we have further found a relation between the induced optical-absorptioncoefficient at 5.8 eV and Ge(1) defects, a linear correlation between Ge(1) and Dn and the absence of acorrelation between the other paramagnetic defects and Dn. These findings suggest that the Dn phenomenologyis closely related to the Ge(1) generation mechanisms and this latter is affected by the oxygen deficiency.