Several radiation defects with effective electron spin $S=1$ have been observed in synthetic $\alpha$-quartz, using room-temperature (RT) electron paramagnetic resonance (EPR) spectroscopy. It turns out that these defects had better be considered as biradicals, i.e., pairs of $S=1∕2$ species. The parameter matrices ${\mathbf{g}}_1$, ${\mathbf{g}}_2$, $\mathbf{D}$ as well as matrices $\mathbf{A}$ describing the hyperfine interactions with two slightly inequivalent ${}^{29}\mathrm{Si}$ nuclei have been determined for the most intense (but RT unstable) such defect, which herein is labeled $E_1^{″}$. The triplet-state approach and the biradical approach are compared. Inter-electron distances have been estimated using magnetic dipole concepts. A structure for center $E_1^{″}$ is proposed, suggesting an oxygen $\left({\mathrm{O}}^0\right)$ vacancy with two unpaired electrons (holes) existing at silicon cations on opposite sides of the cavity, and the model is compared with the observed data and with published results for related single-unpaired electron species. Firm correlations between spin-Hamiltonian parameter matrix principal axes (EPR data) and crystallographic directions (x-ray diffraction data) have been attained.

• Received 31 July 2007
• Accepted 16 October 2007

DOI:https://doi.org/10.1103/PhysRevB.76.214114