Superfast LEDs to improve light-based telecommunications

Duke University researchers have made fluorescent molecules emit photons of light 1,000 times faster than normal - setting a speed record and making an important step toward realizing superfast light emitting diodes (LEDs).

This year's Nobel Prize in physics was awarded for the discovery of how to make blue LEDs, allowing everything from more efficient light bulbs to video screens.

While the discovery has had an enormous impact on lighting and displays, the slow speed with which LEDs can be turned on and off has limited their use as a light source in light-based telecommunications.

"One of the applications we are targeting with this research is ultra-fast LEDs," said Maiken Mikkelsen, an assistant professor at the Duke University in the US.

"While future devices might not use this exact approach, the underlying physics will be crucial," Mikkelsen pointed out.

When fluorescent molecules are placed near intensified light, the molecules emit photons at a faster rate through an effect called Purcell enhancement.

The researchers found they could achieve significant speed improvement by placing fluorescent molecules in a gap between the nanocubes and a thin film of gold.

To attain the greatest effect, the researchers needed to tune the gap's resonant frequency to match the colour of light that the molecules respond to.

They used computer simulations to determine the exact size of the gap needed between the nanocubes and gold film to optimise the setup.

That gap turned out to be just 20 atoms wide. But that was not a problem for the researchers.

"When we have the cube size and gap perfectly calibrated to the molecule, that's when we see the record 1,000-fold increase in fluorescence speed," explained Gleb Akselrod from Mikkelsen's laboratory and first author of the study.

To make future light-based communications using LEDs practical, it is important for researchers to get photon-emitting materials up to speed.

The findings appeared online in the journal Nature Photonics.