Spectral absorption data from crystals of composition KMg1mdash;xNixF3and KZnF3(1 Ni2+) are reported. It is deduced, from a comparison of the spinmdash;orbit energies at 20deg;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 cmminus;1. Absorption by ion pairs and larger clusters has been observed in the nearhyphen;infrared magneticdipole transition. The mechanisms of the various electronic transitions have been studied and the vibrational structure of the electrichyphen;dipole bands interpreted. The four perturbingk= 0 phonon modes observed in the KNiF3spectrum are split in the dilute crystal spectra and correspond to localized vibrations. The mechanism of the transition to the1Egstate has been discussed and it is concluded that it can be described as a singlehyphen;ion excitation which involves strong vibronic spinmdash;orbit coupling with the nearby3T1gastate.
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