Identification of Sn variants of the E′ center in Sn-doped SiO2

Electron paramagnetic resonance data on x-ray irradiated Sn-doped SiO2 samples produced by the sol-gel method are presented. Two variants of Sn-related sites were identified, an orthorhombic one with g(1)=1.994, g(2)=1.986, and g(3)=1.975 and an axial one with g(parallel to)=1.994 and g(perpendicular to)=1.977. A relation between g anisotropy and the spin-orbit coupling constant along the isoelectronic Si-Ge-Sn series strongly supports the attribution to E'-Sn centers consisting of unpaired spins in sp(3) orbitals of three-coordinated Sn sites. An asymmetric 215 mT doublet due to hyperfine interaction with Sn isotopes with non-null nuclear spin confirms this assignment. [S0163-1829(98)08439-2].