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Localization of rare-earth dopants in the lattice of nanocrystalline ZrO2 - EXAFS study
|Roman Pielaszek 1, Anna Wolska 2, Agnieszka Opalińska 1,3, Witold Łojkowski 1, Stefan Mangold 4, Stephen Doyle 4|
1. Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
Selected crystalline lattices, such as YAG or ZrO2, doped with rare earth atoms become effective light sources used for manufacturing of LEDs, lasers and scintillators. Emission efficiency raises with concentration of the rare-earth with the limit posed by solubility of the dopant on the one hand and concentration quenching phenomena on another.
Nanocrystalline host lattice inherits desired optical features of model infinite lattice but allows for much higher solubility of rare earth dopants. Simultaneously, in case of nanocrystalline lattice, the long-distance crystal order is cut on the grain boundary which relaxes quenching.
In the present work we show preliminary EXAFS study of rare-earth atoms buried in zirconia nanocrystals, 10-40nm in diameter. The experiments show that dopants are evenly distributed in nanocrystals and do not segregate even at very high concentrations. Surprisingly, most of dopants are located in monoclinic phase of ZrO2 (zriconia, as synthesized, is usually a mixture of tetragonal and monoclinic phases). This knowledge strongly influences synthesis procedures used to obtain high-intensity luminescent zirconia powders.
Figure below shows average electron density (blue) around Eu dopant in the ZrO2 being mixture of tetragonal and monoclinic phase. Red curve is theoretical density asumming: even distribution of Eu within ZrO2, lack of Eu segregation (e.g. as oxide), non-surface position, most of Eu in monoclinic nanocrystals only (a trace in tetragonal, however) and very high concentration of Eu.
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium C, by Roman Pielaszek
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-06-06 11:22 Revised: 2009-06-07 00:48