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

Electron paramagnetic resonance data on x-ray irradiated Sn-doped (Formula presented) samples produced by the sol-gel method are presented. Two variants of Sn-related sites were identified, an orthorhombic one with (Formula presented) and (Formula presented) and an axial one with (Formula presented) and (Formula presented) A relation between g anisotropy and the spin-orbit coupling constant along the isoelectronic Si-Ge-Sn series strongly supports the attribution to (Formula presented) centers consisting of unpaired spins in (Formula presented) 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. © 1998 The American Physical Society.