Paramagnetic centers in amorphous GeO2

In this work we investigate paramagnetic centers in amorphous germania (alpha-GeO2). We provide an analysis of the Fermi contacts and of the g-tensors calculated by first-principles for the E'-Ge, Ge-Ge and Ge forward-oriented (GeFO) configurations. The electron paramagnetic resonance (EPR) parameters calculated for the Ge-Ge configurations, where the unpaired electron is shared between two Ge nearest neighbors, do not support such a model of the E'-Ge*, nor the latter can be simply regarded as an E'-Ge center with a distorted geometry. A fair agreement with the experimental EPR parameters supports the assignment of the Ge(2) center in a-GeO2 to GeFO configurations. Furthermore we show that electronic levels induced in the bandgap by GeFO configurations are considerably deeper (similar to 1 eV) with respect to those related to the E'-Ge centers. (C) 2015 Elsevier B.V. All rights reserved.