Effect of a Static Electric Field on theRLines of(3d)3Ions in Corundum

Abstract

The pseudo-Stark splitting of the $R$ lines of ${\mathrm{V}}^{2+}$ and ${\mathrm{Mn}}^{4+}$ in ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ has been measured in electric fields up to 170 kV/cm. For fields parallel to the $c$ axis the splitting is 1.5×${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/(V/cm) for ${\mathrm{V}}^{2+}$ and 4.5×${10}^{-5\mathrm{}}$ for ${\mathrm{Mn}}^{4+}$ (compare 5.3×${10}^{-6\mathrm{}}$ for ${\mathrm{Cr}}^{3+}$). There is no detectable splitting for an electric field perpendicular to the $c$ axis. The effect for ${\mathrm{Mn}}^{4+}$ is much greater than one would expect from the oscillator strengths of the crystal-field transitions, which, like the pseudo-Stark splitting, depend primarily on the hemihedral part of the crystal field. The large effect in ${\mathrm{Mn}}^{4+}$ appears to be principally due to the movement of the ion in the field and the consequent change in overlap with its neighbors. The principal effect for the other two ions appears to be polarization of the ion itself.