Blue shifts corresponding to the absorption edge in the UV-A (310–400 nm) range are obtained from ultraviolet (UV) absorption spectra of monodisperse CeO2−x (0<x<0.5) nanoparticles, which are produced as toluene suspensions by a successive microemulsification method. The blue shift of the nanoparticles is inversely proportional to the 2.2 power of the particle size for a direct transition, but no relation is found for an indirect transition. In contrast, the shift for thin films of 100–200 nm thickness exhibits a relation nearly inverse proportional to the square root of the thickness for the direct transition. These relations are different from that for the quantum size effect, though the difference is small for the nanoparticles. A possible explanation for the blue shift is a valence change of the Ce ions.

Blue shift in ultraviolet absorption spectra of monodisperse CeO2−x nanoparticles

Cerium(IV) oxide ultrafine particles were prepared using a reaction within reversed micelles, which was known as a microemulsion method. The ultrafine particles, which were obtained by mixing the water-in-oil microemulsions containing cerium nitrate solution with those of ammonium hydroxide, were characterized by high-resolution electron microscope (HREM) observations. HREM micrographs revealed that nanometer-sized CeO2 particles were formed, and their shapes were uniform. Selected-area electron diffraction patterns of the particles were completely indexed as those of cerium(IV) oxide with the cubic fluorite structure, and the lattice constant calculated from radii of Debye−Sherrer rings was 0.541 nm. Most of the particles were distributed between 2 and 6 nm, and the mean particle size obtained in this method was between 2.6 and 4.1 nm. The size of 2.6 nm is the smallest among the values ever reported for CeO2 particles. Both direct and indirect optical energy gaps of the particles were independent of the...

Characterization of Cerium(IV) Oxide Ultrafine Particles Prepared Using Reversed Micelles

Sonochemical synthesis of cerium oxide nanoparticles-effect of additives and quantum size effect.

Pure phase CeO2 nanorods (about 40?50?nm in diameter and 03?2??m in length) were synthesized through a solvothermal synthesis method The addition of ethylenediamine is critical to obtain CeO2 nanorods Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology The reaction temperature and reaction time also had significant influence on the yield of CeO2 nanorods A possible formation mechanism of CeO2 nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies In addition, the optical properties of CeO2 nanorods were investigated The UV?visible adsorption spectrum and photoluminescence spectrum of the CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively

https://iopscience.iop.org/article/10.1088/0957-4484/16/9/006/pdf

Controlled synthesis of CeO2 nanorods by a solvothermal method

Ordered nanocrystalline mesoporous cerium oxide was successfully synthesized using MCM-48 molecular sieves as a hard template. The long-range ordered mesostructure was characterized by low-angle and wide-angle X-ray diffraction (XRD), N2 adsorption−desorption technique, and transmission electron microscopy (TEM), and the obtained cerium oxide exhibited high similarity to the cubic Ia3d symmetry of the silica template. Due to smaller crystal size, the mesoporous materials have a blue shift in light absorption as compared with nonporous materials. X-ray photoelectron spectrum (XPS) and energy-dispersive X-ray spectrum (EDS) patterns confirm that mesoporous materials possess more surface vacancies than bulk CeO2. Photocatalytic degradation of azodye acid orange 7 under visible light illumination was used as a catalytic test reaction. The activity of mesoporous product in dye decolorization is substantially higher than those for a nonporous sample and TiO2 P25.

Ordered Mesoporous CeO2 Synthesized by Nanocasting from Cubic Ia3d Mesoporous MCM-48 Silica: Formation, Characterization and Photocatalytic Activity

Optical Absorption in Thin Films of Cerium Dioxide and Cerium Dioxide Containing Silicon Monoxide

Measurements of optical absorption of thin film samples of CeO2/SnO2 and CeO2/GeO2 prepared by a co-evaporation process at a pressure in the range 1.06 to 1.33 mPa, and having a thickness of ≈300 nm are reported. It is found that the fundamental optical absorption edge is sharp, much more like that expected for a crystalline material rather than the usual form for amorphous material, and the optical gap is increased by the addition of CeO2 to SnO2 and GeO2 films.



Ce rapport traite de l'absorption des rayons lumineux par des couches minces de CeO2/SnO2 et CeO2/GeO2 de 300 nm d'epaisseur, obtenues par co-evaporation a des pressions entre 1,06 et 1,33 mPa. Les mesures effectuees montrent que la limite d'absorption optique fondamentale est beaucoup plus rapide lorspue le materiel est cristallin -que lorsque l'on utilise la phase amorphe habituelle, et le bandgap optique augmente par l'addition de CeO2 aux echantillons de SnO2 et GeO2.

The Optical Absorption Edge in Thin Amorphous Oxide Films Based on Cerium Dioxide

Optical Absorption in Thin Films of Cerium Dioxide Containing Indium Oxide

Electrical measurements on thin films of In2O3 and In2O3/CeO2 before and after electroforming are reported. The high field conduction (expressed in terms of circulating current I c and base voltage V b) in thin film sandwich structures (MIM, Metal-Insulator-Metal) of Cu-In2O3-Cu and Cu-In2O3/CeO2-Cu is found to obey a relation of the form log I cαV b ½. The electroformed samples show voltage controlled negative resistance (VCNR). Voltage memory, thermal voltage memory and pressure voltage memory effects are observed and the results are explained in terms of the filamentory model of electrical conduction.

Electrical conduction in thin films based on In2O3 and In2O3/CeO2

AC and DC conduction in metal-insulator-metal (MFM) sandwich samples based on CeOz/Cd as a dielectric prepared by the co-evaporation technique has been investigated and the results are in agreement with the behaviour expected of amorphous thin dielectric films.

Z. T. Al-Dhhan

Papers

Optical Absorption in Thin Films of Cerium Dioxide and Cerium Dioxide Containing Silicon Monoxide

The Optical Absorption Edge in Thin Amorphous Oxide Films Based on Cerium Dioxide

Optical Absorption in Thin Films of Cerium Dioxide Containing Indium Oxide

Electrical conduction in thin films based on In2O3 and In2O3/CeO2

Electrical conduction in thin films of CeOz/Cd