Fluorescence and absorption spectra of Ni²⁺in MgO

The electron-beam excited fluorescence spectrum of Ni2+ in single crystals of MgO has been recorded at 77 and 5 degrees K. The observed transitions occur from the 1T2(t5e3), 3T1(t5e3) and 3T2(t5e3) excited terms to the 3A2(t6e2) ground term. Comparison of the fluorescence spectrum with the recorded absorption spectrum, together with consideration of the theoretical transition probabilities, makes possible a differentiation between zero-phonon magnetic-dipole transitions from spin-orbit levels of the excited terms to the ground state and vibronic transitions. The 3T1(t5e3) excited term is stabilized by a strong spin-orbit interaction, whilst the 1T2(t5e3) term is split by a static Jahn-Teller interaction. The phonon density of states is derived and red-shift data for the excited terms are discussed.