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Research Highlight

New nanostructured phosphors for photonics and white LEDs

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Optical images of individual Eu-Al-O nanoribbon waveguides excited by a synchrotron x-ray microbeam at the APS beamline 34-ID. The different emission colors arise from different crystal structures, including a previously unknown tetragonal (blue) and hexagonal (yellow) lattice.
A new family of one-dimensional nanostructures based on novel crystal structures has been discovered that produces strong, tunable, visible-light luminescence. Since the emission colors (purple through red) are controlled by changes in the crystal structure, these new nanoribbons hold promise for enabling both photonic waveguides and high-efficiency phosphors for broad-spectrum, warm-white Light-Emitting Diodes (LEDs).

The nanoribbons are ternary europium aluminate single crystals that are grown by evaporating and recondensing a mixture of Eu-Al-O powders in a well-controlled tube furnace. Structural investigations using both synchrotron x-ray microdiffraction from individual nanocrystals and powder x-ray diffraction reveal that different photoluminescence colors result from different lattice structures and compositions: blue luminescent materials have a tetragonal lattice; green materials have a monoclinic structure; and yellow to red materials have a hexagonal structure. Two classes, tetragonal (blue) and hexagonal (yellow to red), represent new compounds that do not exist as bulk materials. The different local atomic bonds in these compounds give rise to the different excitation spectra. By combining different nanostructures in a phosphor coating and using a blue LED chip for excitation, warm-white-light suitable for indoor illumination has been produced. 

For more information, please contact John Budai, budaijd@ornl.gov.

References:

1. F. Liu, J. D. Budai, J. Z. Tischler, J. Y. Howe, C. Sun, R. S. Meltzer and Z. W. Pan, “New ternary europium aluminate luminescent nanoribbons for advanced photonics,” accepted for publication in Advanced Functional Materials,  doi: 10.1002/adfm.201202539

2. X. Li, J. D. Budai, F. Liu, J. Y. Howe, J. Zhang, X. Wang, Z. Gu, C. Sun, R. S. Meltzer, and Z. W. Pan, “New yellow Ba0.93Eu0.07Al2O4 phosphor for warm-white light-emitting diodes through single-emitting-center conversion,” Nature Publishing Group: Light: Science & Applications 2, (2013). doi:10.1038/lsa.2013.6