Electron-Spin Resonances in Gamma-Ray-Irradiated Aluminum Oxide

Single crystals of $\alpha$-aluminum oxide were subjected to gamma-ray irradiation at 77°K. A single, asymmetric, paramagnetic-resonance absorption was produced with $g_{\mathrm{II}}=2.012\mathrm{}\pm 0.002$ and $g_{\perp }=2.008\mathrm{}\pm 0.002$, where ∥ and ⊥ are with respect to the $c$ axis. The line width is about 50 G at 300 and 77°K. The absorption line has been analyzed as a superposition of three Gaussian lines with the isotropic $g$ values: $g_1=2.020\mathrm{}\pm 0.003$, $g_2=2.006\mathrm{}\pm 0.003$, $g_3=2.006\mathrm{}\pm 0.003$. The component lines are tentatively attributed to two types of centers: a trapped hole localized on an anion adjacent to a cation site which is deficient in positive charge, and an electron trapped at an anion vacancy. The cation site may be vacant, or may contain a monovalent or divalent substitutional impurity.