RAMAN AND ELECTRONIC RAMAN-SPECTRA OF LANTHANIDE IONS IN ELPASOLITE LATTICES

Raman spectra have been recorded from 300-10 K for lanthanide hexachlo roelpasolites, Cs2NaLCl6. Electronic Raman-scattering intensity ratios have been calculated using Judd-Ofelt-Axe theory and are in reasonabl e agreement with experimental results, except for those cases where el ectron-phonon coupling has important consequences. Bands resulting fro m temperature-dependent electron-phonon coupling phenomena have been o bserved not only in the Raman spectrum of Cs2NaYbCl6 but also in that of Cs2NaTmCl6, and the interaction mechanism is discussed. The couplin g element between the coupled a Gamma(5) similar to Gamma(1)+nu(5) pho non-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 TmCl 63-. Excited-state electronic Raman scattering has been observed in th e 120-K Raman spectrum of Cs2NaTmCl6. Using fixed wavelength argon-ion laser lines, there is evidence for a small resonance enhancement of e lectronic Raman-scattering intensity, and the unusual mechanism for th is is discussed. The mixed crystal system Cs2NaGd1-xYbxCl6 exhibits un imodal behavior for the nu(1) and nu(5) vibrations, and the more compl ex 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 wher e electron-phonon coupling effects occur.