Green Technology Forum

Researchers from Clemson University and the École Nationale Supérieure de Physique de Strasbourg in France have developed rare-earth-doped, core-shell LaF₃ nanoparticles that could enable spectral design of luminescent materials [DiMaio et al., Proc. Natl. Acad. Sci., USA (2008) doi: 10.1073/pnas.0711638105].

The broad spectral range of emission from such nanoparticles could find application in light-emitting diodes (LEDs), solar cells, lasers and amplifiers, and biological assaying.

For applications, such nanoparticles should, ideally, have the ability to tailor independent emissions from a codoped material. Until now, it was thought that this could only be achieved by using nanoparticles incorporated into a host matrix where each nanoparticle is doped with a particular rare earth element (i.e. a lanthanide).

Instead, however, the researchers use 10 nm, core-shell LaF₃ nanoparticles with Tb³⁺ and Eu³⁺ dopants constrained to specific individual shells. The distance between shells, and therefore dopants, can be carefully controlled.

This enables, in turn, control over the energy transfer to varying degrees – from zero to partial to total – between the dopants within an individual nanoparticle.

Using three-shell particles, the ratio of the 540-nm Tb³⁺ peak to that of the 590-nm Eu³⁺ peak can be varied from 0.2–2.4. This variation only arises from changes in the internal structure of the nanoparticles, not any compositional or external dimensional changes. The separation between the shells has to be a minimum of >2 nm.

“This work shows that nanoparticles ~10 nm in diameter can have complex core-shell architectures that allow significant tuning of their light emissive properties,” explains Jeffrey R. DiMaio, now at Tetramer Technologies. These nanoparticles, and composites made from them, could be used to engineer specific spectral features.

“The key issue here is that nanoparticles can be engineered to emit at multiple tunable wavelengths from a single optical source,” comments Jean Pierre Leburton of the Beckman Institute for Advanced Science and Technology.

source: nanotoday.com

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