Raman and electronic Raman spectra of lanthanide ions in elpasolite lattices

This is the authors' abstract. We don't add key points for this paper.

Raman spectra have been recorded from 300--10 K for lanthanide hexachloroelpasolites, Cs₂{NaLCl}₆$. Electronic Raman-scattering intensity ratios have been calculated using Judd-Ofelt-Axe theory and are in reasonable agreement with experimental results, except for those cases where electron-phonon coupling has important consequences. Bands resulting from temperature-dependent electron-phonon coupling phenomena have been observed not only in the Raman spectrum of Cs₂{NaYbCl}₆$ but also in that of ${Cs}₂NaTmCl₆, and the interaction mechanism is discussed. The coupling element between the coupled aΓ₅{~}Γ₁+ν₅ phonon-electron states of ³H₆ in Cs₂{NaTmCl}₆$ is estimated to be 20 ${cm}^{{{-}}1}$, and the corrected wave functions for these coupled states enable a consistent reinterpretation to be made of the optical spectra of ${TmCl}₆^{3{{-}}}$. Excited-state electronic Raman scattering has been observed in the 120-K Raman spectrum of ${Cs}₂NaTmCl₆. Using fixed wavelength argon-ion laser lines, there is evidence for a small resonance enhancement of electronic Raman-scattering intensity, and the unusual mechanism for this is discussed. The mixed crystal system Cs₂{NaGd}_{1{{-}}x}Ybₓ{Cl}₆$ exhibits unimodal behavior for the ${{ν}}₁$ and ${{ν}}₅$ vibrations, and the more complex behavior of features in the neighborhood of ${{ν}}₂$ is described. The vibrational energies of the gerade internal ${LCl}₆^{3{{-}}}$ modes (determined from Raman spectra) vary linearly with atomic number of L, except where electron-phonon coupling effects occur.