Energy levels of terbium(III) in the elpasolite Cs₂NaTbCl₆

Abstract

Polarized two-photon excitation (TPE) and emission spectra have been used to locate, and identify the symmetry of, more than 100 energy levels of terbium(II1) in the elpasolite Cs2NaTbC16. 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 the predictions of the one-electron model provide evidence for electron correlation induced by the crystal field (CCF).

4f8–4f8 Ultraviolet absorption spectrum of Cs2NaTbCl6

“…Spectral features correspond to MD zero phonon lines with additional broader structure corresponding to TbCl 3À 6 moiety modes. The agreement with the assignments from TPE spectra [2] is good and confirmatory since the one-photon absorption spectra are subject to very different selection rules. However, it is difficult to assign terminal A 2 levels from either TPE or absorption.…”

“…The levels N = 4-21 below 20 470 cm À1 have been assigned from the infrared and luminescence spectra [5] and are not included. Most CF level energies of Cs 2 NaTbCl 6 are very similar to those of [2], within experimental error, except for the 7 F 5 T 1 level assigned in [5] at 2349 cm À1 . Otherwise, the ultraviolet absorption spectrum of Cs 2 NaTbCl 6 is fully consistent with the energy level scheme of [2], and two further T 1 levels have been identified.…”

“…When complemented by the previously assigned energy levels from one photon emission [3,4] and infrared absorption [5], altogether more than 130 levels were assigned for Cs 2 NaTbCl 6 and 90 for Cs 2 NaTbF 6 [1,2]. Recently, we have calculated two photon absorption (TPA) line strengths for these systems [6], and this, together with some revised matrix elements in the calculation [7], enabled a reassessment to be made of the energy level scheme.…”

“…Denning and co-workers have utilized two-photon excitation (TPE) spectra to investigate and assign the excited 4f 8 states of Tb 3+ in cubic host crystals [1,2]. When complemented by the previously assigned energy levels from one photon emission [3,4] and infrared absorption [5], altogether more than 130 levels were assigned for Cs 2 NaTbCl 6 and 90 for Cs 2 NaTbF 6 [1,2].…”

“…The experimentally-derived energy level scheme of Morrison et al [2] and the recent energy level calculation [6] were also employed as references for the assignment of electronic transitions. It was then found from the absorption spectral assignments that besides vibronic structure, the remaining bands were mainly those corresponding to MD transitions.…”