Artículos SCI

Optical properties and electronic transitions of four oxides, namely zinc oxide, ferric oxide, cerium oxide, and samarium oxide, are determined in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy using primary electron energies in the range 0.3 - 2.0 keV. This technique allows the evaluation of the optical response in these ultraviolet spectral regions of a thin layer of material, and the analysis is straightforward. It is performed within the dielectric response theory by means of the QUEELS-epsilon(k,omega)-REELS software developed by Tougaard and Yubero [Surf. Interface Anal. 36, 824 ( 2004)]. The method consists basically in the fitting of experimentally determined single-scattering electron energy loss cross sections with a parametric energy loss function of the corresponding material, to the one calculated within a dielectric response formalism. The obtained refractive index and extinction coefficients, as well as the identified electronic transitions are compared, when available, with previously published results. 

Uniform, hydrophilic 50 nm diameter Nd3+-doped Ba0.3Lu0.7F2.7 nanospheres are synthesized at 120 degrees C using a singular one-pot method based on the use of ethylene glycol as solvent, in the absence of any additive. The composition and crystal structure of the undoped material are analyzed in detail using ICP and XRD, which reveals a BaF2 cubic crystal structure that is able to incorporate 70 mol% of Lu ions. This finding contrasts with the reported phase diagram of the system, where the maximum solubility is around 30 mol% Lu. XRD proves as well that the Ba0.3Lu0.7F2.7 structure is able to incorporate Nd3+ ions up to, at least 10 mol%, without altering the uniform particles morphology. The Nd-doped particles exhibit near-infrared luminescence when excited at 810 nm. The maximum emission intensity with the minimum concentration quenching effect is obtained at 1.5% Nd doping level. X-ray computed tomography experiments are carried out on powder samples of the latter composition. The sample significantly absorbs X-ray photons, thus demonstrating that the Nd3+-doped Ba0.3Lu0.7F2.7 nanospheres are good candidates as contrast agents in computed tomography.