Influence of Ge doping level on the EPR signal of Ge(1), Ge(2) and E'Ge defects in Ge-doped silica

We present an experimental investigation on the Ge doping level dependence of the Electron Paramagnetic Resonance (EPR) signal spectral features of the Ge(1), Ge(2) and E'Ge defects induced in Ge doped silica. We have studied samples produced by sol-gel or PCVD techniques and doped with different amounts of Ge up to 20% by weight. The samples were gamma or beta ray irradiated and successively they were thermally treated to isolate the EPR signals of the different point defects. The data show that the EPR line shapes of the Ge(1) and the Ge(2) centers are progressively modified for doping level higher than 1%, whereas the line shape of the E'Ge defect appears independent from the doping. Together with the EPR investigation, we have also recorded Raman spectra of the investigated samples. The Ge doping induces detectable modifications of Raman lines when the doping level is higher than 1% by weight. Basing on these observations, the structural modifications detected by Raman spectroscopy are tentatively considered the origin of the changes in the EPR features.