Electronic Absorption Spectrum of Ni(II) in Cubic Perovskite Fluorides. II. Concentration and Exchange Effects

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Abstract
Spectral absorption data from crystals of composition KMg1—xNixF3 and KZnF3 (1% Ni2+) are reported. It is deduced, from a comparison of the spin—orbit energies at 20°K, that the excited states are only weakly perturbed by exchange interactions. The effect on the ground state is relatively large and it is stabilized by about 170 cm−1. Absorption by ion pairs and larger clusters has been observed in the near-infrared magneticdipole transition. The mechanisms of the various electronic transitions have been studied and the vibrational structure of the electric-dipole bands interpreted. The four perturbing k = 0 phonon modes observed in the KNiF3 spectrum are split in the dilute crystal spectra and correspond to localized vibrations. The mechanism of the transition to the 1Eg state has been discussed and it is concluded that it can be described as a single-ion excitation which involves strong vibronic spin—orbit coupling with the nearby 3T1ga state.