Phonon confinement effect in calcium fluoride nanoparticles

Nanocrystalline CaF2 were obtained by ball-milled synthetic fluorite powders. Raman spectra of nanocrystals with average sizes of 10–25 nm are reported and the correlation between the band shape of the only allowed Raman mode at 322 cm−1 and the crystals dimensions is discussed. While in such systems local temperature and pressure effects play a minor role, variations in the shape of the Raman band can be correctly reproduced by a model based on the phonon confinement that effectively takes into account the anisotropy of the phonon dispersion curve.