Electron paramagnetic resonance data on X-irradiated co-doped samples (0.1, 0.5, or 1wt%Sn and 1 or 3wt%Ge), which had been prepared by using the sol-gel method, were presented. Radiation-induced electron paramagnetic resonance signals were observed which were due to Ge- or Sn-induced E' centers: that is, unpaired electrons in the sp3 orbital of 3-fold coordinated Ge or Sn sites. The E' center yield was determined for samples with various Sn/Ge doping ratios. The concentrations of the 2 electron paramagnetic resonance species were not proportional to the dopant contents, since the creation of Sn-E' centers was favored with respect to that of Ge-E'. A lower Ge-E' yield was observed in samples with a higher Sn content, for a given Ge doping. A simple kinetic model showed that the competitive mechanism of Sn-E' creation could not fully explain the data if the creation of Ge-E' and Sn-E' was supposed to be independent; as expected for a randomly distributed non-interacting dopant species. The Ge and Sn sites were instead proposed to be preferentially spatially related.

Electron Paramagnetic Resonance Study of Ge and Sn Doping of SiO2 from Sol-Gel Method. N.Chiodini, F.Meinardi, F.Morazzoni, A.Paleari, R.Scotti, G.Spinolo: Solid State Communications, 1999, 112[10], 565-8