Spin Resonance of ${\mathrm{V}}^{2+}$, ${\mathrm{V}}^{3+}$, ${\mathrm{V}}^{4+}$ in $\alpha$-${\mathrm{Al}}_2$${\mathrm{O}}_3$

The electron-spin resonance absorption properties of vanadium sapphire are reported. It is shown that normally vanadium is predominantly trivalent with a small amount in the tetravalent state. After x or gamma irradiation, vanadium is converted to the divalent state. The hfs component separations for ${\mathrm{V}}^{2+}$, ${\mathrm{V}}^{3+}$, and ${\mathrm{V}}^{4+}$ are about 88, 110, and 140 gauss, respectively. Because of its readily recognizable spin resonance signature, due to its nuclear spin and because of the ease of producing different oxidation states, it is suggested that vanadium may be a suitable probe to study ionization effects in certain solids.