Crystal field calculations of energy levels of the Ni2+ ions in MgO

The electronic energy levels of six-fold coordinated Ni²⁺ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni²⁺ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited ³T _2g state fine structure; however, it does not explain why out of four levels arising from the ³T_2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn-Teller effect.