High-resolution far infrared spectroscopy of the lower energy levels of Cr2+in MgO

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Abstract
High-resolution far infrared spectroscopy has been performed on the lowest-lying energy levels of Cr2+ in a MgO host crystal in magnetic fields up to 25 kG at temperatures between 1.2K and 4.2K. The relevant electromagnetic radiation from 2 cm-1 to 10 cm-1 was produced by using the higher harmonics of klystron radiation, leading to a tunable radiation source for the region between 2 cm-1 and 25 cm-1. From the extrapolated resonance frequencies at zero magnetic field of the electron paramagnetic resonance spectra and the measured temperature dependence of these resonances, an energy level scheme for the Cr2+ ion in MgO has been constructed which is in close agreement with theoretical considerations. The relative positions of the low-lying energy levels can be described with the two parameters 3 Gamma =17.2 cm-1 and D=2.87 cm-1. In addition, the sign of the anharmonicity parameter B was found to be positive. The magnetic field dependence of these low-lying energy levels (described by a g-factor in the case of linear dependence) differs significantly from theoretical predictions. The linewidth of the resonances suggests an upper limit for the lifetime of the T2 level of 3*10-9 s.

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