No abstract

The photocatalytic properties of the anatase form of nanocrystalline TiO 2 doped with lanthanide ions (Eu 3+ , Sm 3+ and Er 3+ ), obtained by a sol-gel preparation method, are studied by means of the degradation of methylene blue. It is observed that the presence of Sm 3+ ion as a dopant significantly improves the photocatalytic activity of anatase TiO 2 with respect to the Eu 3+ or Er 3+ ions.For the understanding of such a catalytic process the charge transport in these systems is studied by an appropriate Monte Carlo simulation which includes phonons, charged impurities and traps. The obtained results evidence the important role of the traps for the transit of the electrons in the systems investigated here. They decrease the diffusion coefficient by about three orders of magnitude with respect to the bulk, from which it is possible to obtain a simple estimate of the reaction rate in agreement with experimental results. All the lanthanide-doped samples show a strong luminescence in the visible region. The emission bands are affected by a notable inhomogeneous broadening, indicating a high disorder of the crystalline environment of the lanthanide ions in the titania host.

No abstract

A new extended theory of electron transport in dense gases is presented. It is shown that positive and negative density effects can be explained in terms of a single unifying theory. The agreement between theory and experiment is extremely good over a wide range of pressure and temperature in gases with a negative effect, such as He and H2. Some further improvements of the theory in gases with elevated polarizability seem to be necessary for a better quantitative agreement with experimental data, even if the agreement in Ar makes us confident that the proposed theoretical approach can be correct. In the light of our unifying theory, previous theoretical models are analyzed and it is shown that almost all can be obtained under special conditions.

No abstract