ABSTRACT
Before returning to the subject of hyperfine interactions in crystals some further remarks on crystal field theory and on the Judd-Ofelt1,2 theory of intensities are required. Since the classical paper of Bethe3, considerable attention has been given to the interpretation of the spectra of f − electron ions substituted into various crystal lattices. The simple theory4−8 based, initially, on the assumption that the substituted ion “sees” a purely electrostatic field with a point symmetry of the lattice site it occupies, met with considerable success. It allowed meaningful assignments to be made of most of the observed crystal field levels and, for the rare earths, the crystal field parameters usually reproduce the observed spectra to a standard deviation of ∼ 10cm−1.
