Luminescent properties of redox active Zr_1-xCe_xO₂ nanoparticles

Mixed cerium-zirconium oxides (Zr_1-xCe_xO₂) has recently made a breakthrough in the field of development of three-way catalysts for automotive converters. As was shown in the number of papers, incorporation of zirconium ions into fluorite-type ceria structure leads to its local distortion accompanied by lowering of the energy of oxygen vacancy formation. This effect leads to both increased oxygen mobility and oxygen storage capacity (OSC) of the mixed cerium-zirconium oxide as compared to pure ceria. While the excellent OSC properties of Zr_1-xCe_xO₂ nanocrystals are widely accepted today, the content and arrangement of oxygen vacancies in these materials are still under discussion. In our previous papers using the methods of conventional luminescent spectroscopy we have determined the relative location of trivalent ions and oxygen vacancies for CeO_2-x and CeO₂:Eu³⁺ nanocrystals and the same techniques can be used for analysis of the processes of oxygen vacancies formation in Zr_1-xCe_xO₂ nanocrystals. In our work we have obtained nanocrystals Ce_1-xZr_xO₂ with different zirconium concentrations (x = 0.1 and 0.2). We have shown that both increase of the concentration of zirconium ions, and transition from oxidizing to reducing atmosphere stimulates formation of additional oxygen vacancies in Zr_1-xCe_xO₂ nanocrystals. Increase of the content of oxygen vacancies in Ce_1-xZr_xO₂ is manifested in the higher intensity of the band formed by 5d → 4f transitions of Ce³⁺ ions (390 nm) due to capture of the electrons remaining at oxygen removal by Ce⁴⁺ ions. (author)