Raman and electronic Raman spectra of lanthanide ions in elpasolite lattices

Raman spectra have been recorded from 300-10 K for lanthanide hexachloroelpasolites, Cs2NaLCl6. 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 Cs2NaYbCl6 but also in that of Cs2NaTmCl6, and the interaction mechanism is discussed. The coupling element between the coupled a Gamma(5) similar to Gamma(1)+nu(5) phonon-electron states of H-3(6) in Cs2NaTmCl6 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 TmCl63-. Excited-state electronic Raman scattering has been observed in the 120-K Raman spectrum of Cs2NaTmCl6. 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 Cs2NaGd1-xYbxCl6 exhibits unimodal behavior for the nu(1) and nu(5) vibrations, and the more complex behavior of features in the neighborhood of nu(2) is described. The vibrational energies of the gerade internal LCl63- modes (determined from Raman spectra) vary linearly with atomic number of L, except where electron-phonon coupling effects occur.