Optical spectra of the elpasolite hexachloride compounds Cs2NaLnCl6, where Ln represents one of the lanthanide ions, are analyzed with a crystal-field Hamiltonian of Oh symmetry. Crystal-field parameters, Bnm, are found that minimize the rms deviation between calculated and experimental energy levels for Ln=Ce, Pr, Nd, Eu, and Tb. A set of ’’smoothed’’ Bnm is found for the lanthanide series that predicts the spectroscopic properties of the remaining eight lanthanide ions. Predicted energy levels and g values are compared with available experimental data for all the lanthanides except Pm and Gd, and magnetic dipole intensities are computed.

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Absorption and fluorescence spectra of Tm'+ in single-crystal LiYF4 were recorded at temperatures between 5 and 77 K, The energy levels for the ground configuration were established from these data with the aid of theoretical calculations. Parameters were obtained that gave a least-squares deviation of 16.9 cm ' between the experimental and calculated energy levels. These calculated levels were obtained by diagonalizing a Hamiltonian that describes the free-ion and crystal-field interactions in a basis of states spanning the 4f" configuration. The free-ion parameters are F, = 462.49, F, = 70.762, F6 --7.6265, g = 2652.8, a = 23.262, P = -761.64, Mo --3.2459, M = 1.4608, M = 0.8202, and M"' = 0.5572, and the crystal-field parameters are B"=358.7, B,p = -607.8 B60 = -173.0, B44 --844.2, and B « --629.2 (all units are crn '). The calculated and crystal-field-split energy levels were in agreement to within 9 cm ' after the calculated energy centroids were adjusted. The S4 symmetry property of the ground state was determined to be I,.