Publication
Title
Infrared absorption and Raman scattering of $OH^{-}$ and $OD^{-}$ stretching-mode vibrations in alkali fluorides : isolated defects
Author
Abstract
 The stretching-mode (SM) of OH- and OD- defects in LiF, NaF, and KF hosts has been studied with Raman scattering and Fourier transform infrared (FTIR) absorption spectroscopy, at temperatures from 4 K to 500 K. In all three hosts the (111) orientation of the OH- molecular axis is confirmed both by polarized Raman spectra and by stress-induced FTIR dichroism. The latter technique also yields the values of the disc-shaped elastic dipole tensor, aligning the OH- parallel to an applied(lll) uniaxial stress with a Curie law. Accurate band-shape analysis of low-temperature FTIR absorption and T-2g Raman spectra yields for low concentrations of OH- in LiF and KF consistent values of their nearest-neighbor reorientational tunneling parameters (Delta = 1.2 and 0.6 cm(-1), respectively). For OH- in NaF and for OD- in all three hosts spectral substructure from tunneling is undetectable in the narrow Lorentzian-shaped SM Lines. The strong temperature broadening that occurs for the SM absorption and T-2g Raman bands and the smaller broadening of the A(1g) line can be fitted with models for the dephasing of the transition by phonons, considering the presence of isotropic and anisotropic dephasing components. In spite of the very different amplitudes of the OH- and OD- SM vibrations, their relative infrared absorption and Raman intensities are found to be very similar; the only exception is an extremely weak oscillator strength of the OD- absorption in KF.
Language
English
Source (journal)
Physical Review B
Publication
2000
Volume/pages
61:6(2000), p. 3989-3999
ISI
000085364700039
Full text (Publisher's DOI)
Full text (open access)
UAntwerpen
 Faculty/Department Research group Publication type Subject Affiliation Publications with a UAntwerp address