Polarized two-photon excitation (TPE) and emission spectra have been used t
o locate, and identify the symmetry of, more than 100 energy levels of terb
ium(III) in the elpasolite Cs2NaTbCl6. These are assigned with the aid of a
one-electron crystal field Hamiltonian. In many cases the assignments were
verified by modelling the Zeeman interaction. Systematic deviations from t
he predictions of the one-electron model provide evidence for electron corr
elation induced by the crystal field (CCF).