The ligand-field spectrum of Fe3+ in garnets

The ligand-field spectra of garnets bearing Fe³⁺ exclusively at the octahedral as well as at the octahedral and tetrahedral sites have been studied at energies between 8000 and 30 000 cm^?1. The absorption bands up to 28 000 cm^?1 have been assigned by comparison of experimental and calculated transition energies obtained by a complete solution of the d⁵ energy matrices. The Racah parameters of Fe³⁺ in both positions have been reinterpreted using a constant $\text{C}\text{B}$ ratio evaluated from the gaseous Fe³⁺ ion. It was found that the octahedral B parameters are always larger than the tetrahedral ones. The results are consistent with isomer shifts of ⁵⁷Fe and the observed structural features in oxide garnets.