Confinement effects in quasi-stoichiometric CeO2 nanoparticles

This paper deals with the analysis of structural and electronic effects of size in quasi-stoichiometric CeO2 nanoparticles prepared by a microemulsion method. The preparation method yields highly controlled materials in terms of particle size distribution and chemical oxidation state, with the presence of Ce(III) species only below an average particle size of ca. 8 nm. The rather low quantity of Ce reduced ions produces marked differences with confinement effects previously reported in the literature. A steady behavior of the fluorite lattice parameter is observed as a function of size in the 5-10 nm range. In this range, the bandgap displays a small decrease of ca. 0.1 eV, with significant differences from the behavior expected on the basis of the effective mass approximation. These structural and electronic properties are rationalized on the basis of the characterization of the materials.