  Titanium dioxide (TiO2) nanocrystals were prepared by wet chemical method and
characterized by x-ray diffraction (XRD), transmission electron microscopy
(TEM), Raman scattering (RS) and photoluminescence (PL). The X-ray diffraction
shows the formation of nanocrytalline TiO2 of average sizes 7 nm and 15 nm for
two samples. The x-ray diffraction, transmission electron microscopy (TEM) and
Raman scattering shows that the TiO2 nanocrystals has anatase crystal structure
for both samples. The PL intensity of the smaller particle is more, which has
been attributed to defects and particle size variation. A modified phonon
confinement model with the inclusion of size distribution, a new confinement
function for TiO2 nanocrystals and averaged dispersion curves for most
dispersion phonon branch (G-X direction) has been used to interpret the size
variation of Raman spectra. The obtained Raman peak shift and FWHM agree will
the experimental data. Our observations suggest that phonon confinement effects
are responsible for a significant shift and broadening for the Raman peaks.
