Answers are grounded in this paper and cite their sources.
The addition of an anisotropic spin-orbit coupling term to the crystal field Hamiltonian predicts extra contributions to the energies of the electronic states. An estimate of the magnitude of these contributions for Yb3+:CaF2 and Pr3+:PrCl3 predicts a very small effect.
No takes yet. Share an insight, caveat, or question.
J. E. Lowther (1972) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: