Ge(2), Ge(1) and Ge-E' centers in irradiated Ge-doped silica: A first-principles EPR study

We present a first-principles investigation of Ge paramagnetic centers in Ge-doped vitreous silica (v-SiO2) based on calculations of the electron paramagnetic resonance (EPR) parameters. We infer, by analyzing g-values differences with respect to our Ge-E' configurations, that the EPR signal of the Ge(2) center may arise from Ge forward-oriented (Ge-FO) configurations, where the unpaired spin is localized at a three-fold Ge atom featuring a weak bond with a three-fold O atom, ~ 1.9 °A long. Moreover we show that two-fold Ge atoms, i.e. the germanium lone pair centers (GLPC), under irradiation can easily convert into Ge-FO configurations consistently with experimental observations.