LAUSR

Ceria (CeO2) nanocrystals dispersed in silica were prepared by sol-gel, a very suitable method for large-scale production. The formation of cubic fluorite structure of CeO2 nanocrystals was confirmed by XRD, TG-DTA and TEM. The average nanocrystalline size has been calculated ~3-5 nm using Debye-Scherrer formula for different annealed samples. The calculated nanocrystalline sizes were compared with W-H plot and TEM histograms. Different structural parameters like microstrain, lattice constant, dislocation density, X-ray density and activation energy were also calculated for all prepared samples. We have examined the photoluminescence (PL) due to defect centers and Ce3+ ions present in prepared nanopowder which were excited at two different wavelengths. PL study revealed the effect of annealing on the emission spectra and resulted that the emission efficiency of direct excitation at λex = 325 nm was enhanced with respect to the indirect λex = 250 nm. The emission produced from CeO2 nanocrystals dispersed in amorphous silica matrix has been influenced by many factors such as the modification of the ligand field around the Ce3+ ions in silica, presence of hydroxyl ions and annealing temperature also. Detailed Energy transfer mechanism has been explained with all possible transition lines.