Near-Infrared Fluorescence and Absorption Spectra of Co2+ and Ni2+ in MgO

The electron-beam excited fluorescence spectra of Co2+ and Ni2+ in single crystals of MgO have been recorded at 77° and 4.2°K. For Co2+ the observed transitions occur from the E(t62e) and T24(t4e3) excited terms to the T14(t5e2) ground terms, and for Ni2+ from the Ti3(t5e3) to the A23(t6e2) terms. Comparison of the fluorescence spectra with the appropriate absorption spectra enables an unambiguous indentification of the zero-phonon magnetic-dipole transitions from spin-orbit levels of the excited terms to the ground spin-orbit level for both Co2+ and Ni2+. The splitting of these transitions is discussed. The lattice vibrational sidebands of the Co2+ and Ni2+ fluorescence and absorption spectra may be analyzed in terms of the same two or three phonon modes.