Several radiation defects with effective electron spin S=1 were observed in synthetic α-quartz, using room-temperature electron paramagnetic resonance spectroscopy. It turns out that these defects had better be considered as bi-radicals, i.e., pairs of S=1/2 species. The parameter matrices g1, g2, D as well as matrices A describing the hyperfine interactions with two slightly inequivalent 29Si nuclei were determined for the most intense (but room-temperature unstable) such defect, which herein was labelled E1”. The triplet-state approach and the bi-radical approach were compared. Inter-electron distances were estimated using magnetic dipole concepts. A structure for center E1” was proposed, suggesting an oxygen (O0) vacancy with 2 unpaired electrons (holes) existing at Si cations on opposite sides of the cavity, and the model was compared with the observed data and with published results for related single-unpaired electron species. Firm correlations between spin-Hamiltonian parameter matrix principal axes and crystallographic directions were attained.

Biradical States of Oxygen-Vacancy Defects in α-Quartz. R.I.Mashkovtsev, D.F.Howarth, J.A.Weil: Physical Review B, 2007, 76[21], 214114 (11pp)