SAIP 2011 Support
Effect of annealing on the Ce3+/Ce4+ ratio measured by XPS in luminescent SiO2:Ce
Presented by Mr. Hassan SEED AHMED on 13 Jul 2011 from 17:00 to 19:00
Type: Poster Presentation
Track: Track A - Condensed Matter Physics and Material Science
<p>Ce doped silica has potential applications for a luminescent material as phosphors for cathodoluminescence, scintillators and detectors. Ce ions can occur in a trivalent or a tetravalent state: only the trivalent Ce<sup>3+</sup> state with a single 4f electron is optically active, while the tetravalent Ce<sup>4+</sup> ion is non-luminescent. X-ray photoelectron spectroscopy (XPS) is a suitable technique to investigate the oxidation states of Ce in cerium oxides and such studies have been carried out because of the importance of CeO<sub>2</sub>/Ce<sub>2</sub>O<sub>3</sub> conversion in automotive exhaust catalysts. However, the XPS Ce(3d) spectrum of cerium oxide is rather complex as it contains ten closely spaced and overlapping peaks on a strong background. The main challenge is to obtain accurate fits to experimental data while still maintaining a good physical basis for the fitting parameters. The analysis of Ce in SiO<sub>2</sub>:Ce is even more challenging since the Ce concentration for luminescent samples is only in the region of 1%. Although it has been experimentally shown that to improve the luminescence efficiency of Ce doped silica it can be useful to anneal the glass in a reducing atmosphere, with the implication that this increases the concentration of Ce<sup>3+</sup> luminescent ions, we are not aware of XPS measurements that correlate the relative concentrations of the Ce<sup>3+</sup> and Ce<sup>4+</sup> ions to the luminescent properties. In this work, cerium doped silica was prepared by the sol-gel method. The effect of annealing temperature and atmosphere on the luminescent properties are correlated to XPS measurements of the oxidation state of Ce in the samples.
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