Estudo da influência dos íons terras raras Er3+, Eu3+ e Pr3+ nas propriedades fotoluminescentes e eletroquímicas do CeO2

Abstract

Nanostructures of pure CeO2 and doped with 1.0; 2.0 and 4.0 mol% of rare earths (RE), Er3+, Eu3+ and Pr3+, were prepared using the microwave assisted hydrothermal method. The crystallite size of the materials varied between 5 and 13 nm, being the lower values observed for the CeO2 samples doped with 1.0 mol% of the RE3+ ions, indicating that this concentration inhibited more effectively the crystallites growth. The insertion of RE3+ ions into the CeO2 crystalline lattice generated the formation of extrinsic oxygen vacancies (Vö), according to the Raman spectra. The coexistence of the Ce3+ and Ce4+ ions in the pure CeO2 sample was confirmed by XPS and UV-Vis measurements indicated the coexistence of Pr3+ and Pr4+ ions in the CeO2 doped with Pr3+ ions samples. Hexagonal nanoparticles with sizes between 5 and 12 nm for pure oxide and doped with Eu3+ ions were observed by TEM images. The specific surface area values of the materials varied between 55 and 163 m2 g-1. All samples presented photoluminescent emission in the visible region indicating an order-disorder degree at short and medium reaches. The samples of pure CeO2 and doped with Pr3+ ions showed a broad band photoluminescent emission. The emission spectra of Er3+ doped samples indicated a quenching of photoluminescence with increasing dopant ion concentration. The emission profile of the samples doped with europium indicated that Eu3+ ions were inserted into the CeO2 crystalline lattice occupying a single type of symmetry site. Pure and doped CeO2 films were deposited on the graphite substrate and evaluated as component of battery based on manganese ions. Galvanostatic charge/discharge tests indicated that the electrochemical properties of CeO2 are dependent of the dopant concentration, crystallite size and specific surface area. The sample of CeO2 doped with 1.0 mol% Eu3+ presented the best electrochemical performance, with specific capacity of 372.49 mAh g-1 in a current density of 3.6 mA cm-2 and is promising to be used in batteries based on manganese ions.