Far-Infrared Spectrum of Al2O3:V4+

Two far-infrared lines, 28.1 and 52.8 cm−1, were observed in three different vanadium corundum samples. These lines are interpreted as transitions from the ground state to the first two excited states of Al2O3:V4+. Oxidation and x-ray irradiation data support this assignment. As with the isoelectronic Ti3+ ion in Al2O3, the number of levels is as predicted by crystal-field theory, but their spacing is much less. The far-infrared spectrum of Al2O3:V4+ reported here is in substantial agreement with the results of a recent calculation of 3d1 impurity ions in Al2O3:V4+ in which crystal-field theory is extended by including the dynamic Jahn–Teller effect. It also is consistent with the observation of a new spin resonance spectrum at 4.2°K in vanadium corundum attributed to Al2O3:V4+. The widths of these lines have been measured as a function of temperature and explained satisfactorily on the basis of lifetime broadening due to direct phonon processes. The frequency shifts of these lines as a function of temperature have also been measured, but the data are still not well understood at the present time.