Duke Researchers Speed Up Fluorescence for Faster Turn-on LEDs

Duke University researchers have made fluorescent molecules emit photons of light 1,000 times sooner after being turned on than normal.  While LEDs appear to turn on instantly, they are apparently not fast enough to make light-based communications truly practical.  Modern telecommunications systems, operate nearly a thousand times faster. Atoms in an LED can emit about 10,000 photons when the LED is turned on. The researchers sandwiched fluorescent molecules between metal nanocubes and a gold film to achieve record photon emission rates from the molecules.  The results appear online October 12 in Nature Photonics.

“One of the applications we’re targeting with this research is ultrafast LEDs,” said Maiken Mikkelsen, an assistant professor of electrical and computer engineering and physics at Duke. “While future devices might not use this exact approach, the underlying physics will be crucial.”

Mikkelsen’s group created 75-nanometer silver nanocubes and trapped light between them, producing much more intense light.  Through an effect called Purcell enhancement,  the molecules emit photons at a faster rate when fluorescent molecules are placed near intensified light.

The group with the help of co-author David R. Smith, the James B. Duke Professor and Chair of Electrical and Computer Engineering at Duke, used computer simulations to determine the exact size of the gap between the nanocubes and gold film so that the gap’s resonate frequency maximized the photon emission rate for the color of light that the molecules respond to. The optimum gap was just 20 atoms wide.  Because the experiment used many randomly aligned molecules, the researchers believe they can get the emission rate even higher.