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

Abstract

The absorption spectrum of samples of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ doped with Ti, V, and Cr has been measured at 4.2\ifmmode^\circ\else\textdegree\fi{}K over the frequency range 5-120 ${\mathrm{cm}}^{\ensuremath{-}1}$ in applied magnetic fields up to 55 kOe. In ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:Ti, absorption lines were observed at 37.8 and 107 ${\mathrm{cm}}^{\ensuremath{-}1}$; these were due to transitions between the ground and first excited states of the ${\mathrm{Ti}}^{3+}$ ion in a modified ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ crystalline field. The Zeeman splitting of the observed lines yielded ${g}_{0\ensuremath{\parallel}}=1.11\ifmmode\pm\else\textpm\fi{}0.03$, ${g}_{1\ensuremath{\parallel}}=2.00\ifmmode\pm\else\textpm\fi{}0.06$, and ${g}_{0\ensuremath{\perp}}$, ${g}_{1\ensuremath{\perp}}l0.1$ for the ground and first excited states. Similar results were observed from the isoelectronic ${\mathrm{V}}^{4+}$ ion in the ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:V sample. Zero-field absorption lines were observed at 28.1 and 53 ${\mathrm{cm}}^{\ensuremath{-}1}$, with $g$ values for the ground and first excited states of ${g}_{0\ensuremath{\parallel}}={g}_{1\ensuremath{\parallel}}=1.43\ifmmode\pm\else\textpm\fi{}0.04$ and ${g}_{0\ensuremath{\perp}}$, ${g}_{1\ensuremath{\perp}}l0.2$. The predicted energy levels of a single $d$ electron in the ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ crystalline field modified by a dynamic Jahn-Teller effect are in satisfactory agreement with these data. An absorption line observed at 8.25 ${\mathrm{cm}}^{\ensuremath{-}1}$ in ${\mathrm{Al}}_{2}$${\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 ${g}_{\ensuremath{\parallel}}=1.92\ifmmode\pm\else\textpm\fi{}0.03$ and ${g}_{\ensuremath{\perp}}=1.74\ifmmode\pm\else\textpm\fi{}0.02$. A 15-cm length of 1% ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:Cr showed no absorption lines for any value of magnetic field, indicating that the transitions between the ${\mathrm{Cr}}^{3+}$ ion-pair levels known to exist in this energy region are strongly forbidden. Samples of ruby reported to show far-infrared absorption lines were tested, and it was found that the splitting of the observed lines in a magnetic field was consistent with the assumption that they were due to ${\mathrm{Ti}}^{3+}$ as an unintentional impurity.