Energy levels of terbium(III) in the elpasolite Cs₂NaTbF₆

Polarized two-photon excitation (TPE) and emission spectra are presented for terbium(III) in the elpasolite Cs₂NaTbF₆. Almost 90 levels of unambiguous symmetry have been assigned up to 35 000 cm⁻¹ with the aid of a one-electron crystal field Hamiltonian. This represents the most complete and extensive data set so far reported for a lanthanide ion at a cubic site. Large deviations from the predictions of the one-electron crystal field model are observed in the splitting of a number of multiplets. These are discussed in terms of the correlation crystal field (CCF).