Excitation and absorption spectra of Cs2NaErCl6

From the detailed assignment of the 15K excitation and absorption spectra, the energy level scheme given by previous authors is shown to be incorrect for the excited terms 4 I 13/2, 4 I 11/2, 4 F 7/2 and 4 F 5/2 of Er3+ in Cs2NaErCl6. Additional data for the 4 I 9/2 term enable the first thirty excited states of Er3+ to be located in this elpasolite lattice. The luminescence behaviour of Cs2NaErCl6 is unusual in that a green-ultraviolet upconversion takes place, and that luminescence is expected but not observed from the 4 F 5/2 term. The excitation spectra are used to elucidate the mechanisms of these processes.