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Issue 46, 2009
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Probing local structure in the yellow phosphor LaSr2AlO5 : Ce3+, by the maximum entropy method and pair distribution function analysis

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Abstract

The compound LaSr2AlO5 was recently introduced as a competitive Ce3+ host material for blue-pumped yellow phosphors for use in white light emitting diodes. A crucial feature of the crystal structure of LaSr2AlO5 is that La, which is the host site for Ce3+, is located in the 8h positions of the I4/mcm crystal structure, a site equally shared with Sr. While the average crystal structure of LaSr2AlO5 as revealed by Rietveld analysis of laboratory and synchrotron X-ray diffraction data suggests nothing untoward, maximum entropy method analysis of the synchrotron X-ray data reveals the existence of conspicuous non-sphericity of the electron density. Pair distribution function analysis of the data suggests that despite their occupying the same crystallographic site, La and Sr possess distinct coordination environments, and the environment around La is more compact and regular than the environment suggested by the Rietveld refinement of the average structure. The absorption and emission from Ce3+ centers is controlled by the local coordination and symmetry, and the use of powerful new tools in unraveling details of these strengthens the rational search for new phosphors for solid state white lighting.

Graphical abstract: Probing local structure in the yellow phosphor LaSr2AlO5 : Ce3+, by the maximum entropy method and pair distribution function analysis

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Article information


Submitted
30 Jun 2009
Accepted
21 Sep 2009
First published
15 Oct 2009

J. Mater. Chem., 2009,19, 8761-8766
Article type
Paper

Probing local structure in the yellow phosphor LaSr2AlO5 : Ce3+, by the maximum entropy method and pair distribution function analysis

W. B. Im, K. Page, S. P. DenBaars and R. Seshadri, J. Mater. Chem., 2009, 19, 8761
DOI: 10.1039/B912793C

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