Hyperfine, Superhyperfine, and Quadrupole Interactions forV4+in Tetragonal GeO2

Single crystals of vanadium-doped tetragonal Ge${\mathrm{O}}_2$ have been studied at 300 and 92 K by electron-spin resonance. The observed spectra are attributed to tetravalent vanadium ions ($3d^1$) substitutional at the two inequivalent cation sites. With the choice of axes $\overrightarrow{\mathrm{x}}\parallel \left[\overline{1}10\right]$, $\overrightarrow{\mathrm{y}}\parallel \mathrm{}\left[001\right]\mathrm{}$, and $\overrightarrow{\mathrm{z}}\parallel \mathrm{}\left[110\right]\mathrm{}$, the spin-Hamiltonian parameters obtained at 300 K from the hyperfine, super-hyperfine, and forbidden-transition spectra are $g_x=1.9467\mathrm{}$, $g_y=1.9211\mathrm{}$, $g_z=1.9638\mathrm{}$; $A_x=18.48\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_y=37.27\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_z=134.63\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $P_x=-0.44\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $P_y=-0.35\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $P_z=+0.79\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; $A_{\mathrm{ax}}=8.4\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_{\mathrm{ay}}=8.8\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$,