Optical detection of magnetic resonance in the vibronic sidebands of R and N lines in MgO:Cr³⁺

Measurements of ODMR in the excited states of Cr³⁺ ions in cubic and tetragonal sites in MgO have been used to elucidate the nature of the vibronic sidebands. A comparison of the experimental spectra for zero-phonon line and vibronic sideband with the theoretically calculated selection rules shows that interaction with T_2u odd-parity modes of vibration is the dominant interaction giving rise to the vibronic sidebands.