PHONON STRUCTURE OF RAMAN-SCATTERING SPECTRA OF LIH CRYSTALS

Raman scattering of light in cubic 7LiH and 6LiH crystals at excitation in the range from 514 to 250 nm is investigated experimentally. Raman spectra of pure crystals are measured at 300 K. For the first time, Raman scattering is found to consist of two components. These components are (1) resonant Raman scattering and (2) nonresonant Raman scattering. Resonant Raman spectrum is obtained and identified as the density of states function of V(c-)-type defect, whereas the nonresonant Raman spectrum is obtained and identified as the two-phonon spectrum of LiH. Interesting behaviour of this two-phonon spectrum is found and used as a basis of the original assignment method. Comparison with data from lattice-dynamics calculations gives very close agreement and identifies the modes as originating essentially from X, W, and K points at the Brillouin-zone edges.