Trapped-hole defects in SrO

We report the successful production of $V^{-}$ and $V^0$ defects in SrO. Since hydrogen has been found to be necessary for $V^{-}$ formation in MgO, SrO single crystals were intentionally doped with hydrogen during growth. Both these defects were detected after a short $\gamma$ irradiation at 77 K in crystals previously irradiated with high doses of either neutrons, electrons, or $\gamma$ rays. Electron-paramagnetic-resonance (EPR) measurements showed that the $V^{-}$ center exhibits $〈100〉$ axial symmetry at 77 K characterized by $g_{\parallel }=2.0013\mathrm{}\left(2\right)\mathrm{}$ and $g_{\perp }=2.0705\mathrm{}\left(2\right)\mathrm{}$. At 270 K, the EPR spectrum consists of a single thermally-averaged isotropic line at $g=2.047\mathrm{}\left(1\right)\mathrm{}$. An extensive electron-nuclear double-resonance search at 4.2 K revealed no charge-compensating impurities associated with this center. The $V^0$ center also displays $〈100〉$ axial symmetry at 77 K with the following parameters: $S=1\mathrm{}$, $g_{\parallel }=2.0012\mathrm{}\left(2\right)\mathrm{}$, $g_{\perp }=2.0748\mathrm{}\left(2\right)\mathrm{}$, and $D=127.05\mathrm{}\left(5\right)\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The absence of $V^0$ signals at 4.2 K established that the $S=1\mathrm{}$ triplet state is an excited state. At ∼ 210 K, the $V^0$ centers begin to decay into the more stable $V^{-}$ center. The latter has a room-temperature half-life of ∼ 25 min. Additional defects are also reported. In particular an $S=I=\frac{1}{2}$ axial center is tentatively identified as an ${\mathrm{}\left(\mathrm{OF}\right)\mathrm{}}^{2-}$ molecular ion oriented along $〈111〉$ directions.