Energy levels of terbium(III) in the elpasolite Cs2NaTbBr6. I. Luminescence and two-photon excitation spectroscopy

Fluorescence and two-photon excitation (TPE) spectra are reported for a single crystal of the elpasolite, Cs2NaTbBr6, at low temperatures. Energy levels of the f8 Tb(III) manifold are located and assigned in the range up to 39 400 cm−1 A cubic to tetragonal phase transition occurs below ∼155K. Small spectral splittings in the low-temperature tetragonal phase were satisfactorily simulated and assigned by adding a tetragonal perturbation to the octahedral crystal-field Hamiltonian. Discounting these splittings, more than 100 cubic crystal-field levels can be confidently identified. In several multiplets, substantial deviations are found between the magnitude of the observed splittings and the predictions of an empirical one-body crystal-field Hamiltonian that has been fitted to the full data set. These deviations are relatively more pronounced than in the chloride and fluoride analogues.