Ultraviolet f→f emission and crystal field analysis for Er³⁺in Cs₂NaErCl₆

Luminescence is reported from the2I11/2level of Er3+, in the cubic elpasolite lattices Cs2NaErCl6and Cs2NaYCl6. Altogether, with the use of ultraviolet laser excitation, 11 transitions from2I11/2Γ7(at 40 668 cm-1) to lower term multiplets have been observed and assigned. Transitions are also reported from the2K13/2Γ6level at 32 613 cm-1. The absence of emission from2P3/2(at 31 367 cm-1) under the experimental conditions is rationalized. Up-conversion to2H(2)9/2, which is not due to two-photon absorption, is reported for Cs2NaErCl6under blue pulsed laser excitation. Trap emission from2G9/2defect sites has been observed under ultraviolet excitation. A preliminary investigation has been made of the electronic absorption spectra of Cs2NaErCl6and 58 Kramers quartet and doublet levels have been assigned, with a further 18 levels uncertain. The energy-level fit to 58 levels with total degeneracy 180 has been performed with a mean deviation of 20.4 cm-1, which is improved to 16.8 cm-1if an empirical correction to the diagonal reduced matrix element of U4for the2H(2) term is included. The average error is similar for the 18 uncertain levels (total degeneracy 52). A comparison is included with the energy-level parametrizations of other Er3+systems.