Making light-emitting diodes (LEDs) from nanocrystals could lead to significant energy savings according to researchers who have designed devices that can achieve colour conversion efficiencies of more than 10%. Colour-conversion in traditional LED light sources involves the emission of a high-energy photon, which is absorbed by a phosphor and then re-emitted at longer wavelengths. Victor Klimov and colleagues1 at the Los Alamos and Sandia national laboratories in the US have now made LEDs that directly excite the phosphor via nonradiative energy transfer, eliminating the energy losses associated with the intermediate steps in the colour-conversion process.
The LED consists of an indium gallium nitride (InGaN) quantum well sandwiched between a p-doped GaN barrier below and a thin (3 nm) n-type GaN cap above, with a single layer of cadmium selenide nanocrystals on top acting as the phosphor. The phosphor is excited by direct exciton transfer from the quantum well. Klimov and co-workers report colour-conversion efficiencies of about 13%, which is significantly higher than values obtained with the traditional absorption-re-emission approach in a similar device structure. The new design could lead to improved efficiencies compared to both phosphor-based structures and stand-alone LEDs.
Achermann, M. A. et al. Nano Lett. doi:10.1021/nl060392t (2006).
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Chun, A. New look for LEDs. Nature Nanotech (2006). https://doi.org/10.1038/nnano.2006.16