Far-Infrared Spectra ofAl2O3Doped with Ti, V, and Cr

The absorption spectrum of samples of ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ doped with Ti, V, and Cr has been measured at 4.2°K over the frequency range 5-120 ${\mathrm{cm}}^{-1\mathrm{}}$ in applied magnetic fields up to 55 kOe. In ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$:Ti, absorption lines were observed at 37.8 and 107 ${\mathrm{cm}}^{-1\mathrm{}}$; these were due to transitions between the ground and first excited states of the ${\mathrm{Ti}}^{3+}$ ion in a modified ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ crystalline field. The Zeeman splitting of the observed lines yielded $g_{0\parallel }=1.11\mathrm{}\pm 0.03$, $g_{1\parallel }=2.00\mathrm{}\pm 0.06$, and $g_{0\perp }$, $g_{1\perp }<0.1\mathrm{}$ for the ground and first excited states. Similar results were observed from the isoelectronic ${\mathrm{V}}^{4+}$ ion in the ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$:V sample. Zero-field absorption lines were observed at 28.1 and 53 ${\mathrm{cm}}^{-1\mathrm{}}$, with $g$ values for the ground and first excited states of $g_{0\parallel }=g_{1\parallel }=1.43\mathrm{}\pm 0.04$ and $g_{0\perp }$, $g_{1\perp }<0.2\mathrm{}$. The predicted energy levels of a single $d$ electron in the ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ crystalline field modified by a dynamic Jahn-Teller effect are in satisfactory agreement with these data. An absorption line observed at 8.25 ${\mathrm{cm}}^{-1\mathrm{}}$ in ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$:V was attributed to the spin-orbit splitting of the lowest electronic state of the ${\mathrm{V}}^{3+}$ ion. The Zeeman splitting of this line is in excellent agreement with the appropriate spin Hamiltonian with the parameters