Ultravioletf→femission and crystal field analysis forEr3+

Luminescence is reported from the ${}^{2}{\mathrm{I}}_{11/2}$ level of ${\mathrm{Er}}^{3+},$ in the cubic elpasolite lattices ${\mathrm{Cs}}_{2}{\mathrm{NaErCl}}_{6}$ and ${\mathrm{Cs}}_{2}{\mathrm{NaYCl}}_{6}.$ Altogether, with the use of ultraviolet laser excitation, 11 transitions from ${}^{2}{\mathrm{I}}_{11/2}$ ${\ensuremath{\Gamma}}_{7}$ (at 40 668 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) to lower term multiplets have been observed and assigned. Transitions are also reported from the ${}^{2}{\mathrm{K}}_{13/2}$ ${\ensuremath{\Gamma}}_{6}$ level at 32 613 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The absence of emission from ${}^{2}{\mathrm{P}}_{3/2}$ (at 31 367 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) under the experimental conditions is rationalized. Up-conversion to ${}^{2}\mathrm{H}{(2)}_{9/2},$ which is not due to two-photon absorption, is reported for ${\mathrm{Cs}}_{2}{\mathrm{NaErCl}}_{6}$ under blue pulsed laser excitation. Trap emission from ${}^{2}{\mathrm{G}}_{9/2}$ defect sites has been observed under ultraviolet excitation. A preliminary investigation has been made of the electronic absorption spectra of ${\mathrm{Cs}}_{2}{\mathrm{NaErCl}}_{6}$ and 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 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, which is improved to 16.8 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ if an empirical correction to the diagonal reduced matrix element of ${\mathrm{U}}^{4}$ for ${\mathrm{the}}^{2}$H(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 ${\mathrm{Er}}^{3+}$ systems.