The absorption spectrum of samples of Al2O3 doped with Ti, V, and Cr has been measured at 4.2°K over the frequency range 5-120 cm-1 in applied magnetic fields up to 55 kOe. In Al2O3:Ti, absorption lines were observed at 37.8 and 107 cm-1; these were due to transitions between the ground and first excited states of the Ti3+ ion in a modified Al2O3 crystalline field. The Zeeman splitting of the observed lines yielded g0=1.11±0.03, g1=2.00±0.06, and g0, g1<0.1 for the ground and first excited states. Similar results were observed from the isoelectronic V4+ ion in the Al2O3:V sample. Zero-field absorption lines were observed at 28.1 and 53 cm-1, with g values for the ground and first excited states of g0=g1=1.43±0.04 and g0, g1<0.2. The predicted energy levels of a single d electron in the Al2O3 crystalline field modified by a dynamic Jahn-Teller effect are in satisfactory agreement with these data. An absorption line observed at 8.25 cm-1 in Al2O3:V was attributed to the spin-orbit splitting of the lowest electronic state of the V3+ ion. The Zeeman splitting of this line is in excellent agreement with the appropriate spin Hamiltonian with the parameters g=1.92±0.03 and g=1.74±0.02. A 15-cm length of 1% Al2O3:Cr showed no absorption lines for any value of magnetic field, indicating that the transitions between the Cr3+ 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 Ti3+ as an unintentional impurity. © 1969 The American Physical Society.
