p2p news / p2pnet: LEDs (light emitting diodes) have been around for ever. Microscopic beads called quantum dots are newer. But put them together and you end up with a hybrid LED which could mean the end of the light bulb.

Post-doctoral student and electron microscopist James McBride is interested in quantum dots, says David Salisbury on the Vanderbilt University site.

McBride thought the structure of small-sized dots might offer new insights into their growth process, so he asked Michael Bowers, the graduate student who created them, to make a batch for further study but, “I made him a batch and he came back to me and asked if I could make them any smaller,” says Bowers.

A second batch of even smaller nanocrystals followed, but McBride wanted something smaller still, so Bowers, “made a batch of the smallest quantum dots he knew how to make,” says the story, going on:

“It turns out that these were crystals of cadmium and selenium that contain either 33 or 34 pairs of atoms, which happens to be a ‘magic size’ that the crystals form preferentially. As a result, the magic-sized quantum dots were relatively easy to make even though they are less than half the size of normal quantum dots.

“After Bowers cleaned up the batch, he pumped a solution containing the nanocrystals into a small glass cell and illuminated it with a laser.”

And that’s when the accidental discovery came.

“I was surprised when a white glow covered the table,” Bowers says. “The quantum dots were supposed to emit blue light, but instead they were giving off a beautiful white glow.”

The picture, top right, shows Bowers at the flow cell admiring the white light produced by the magic-sized quantum dots,

The Vanderbilt researchers are the first to report making quantum dots that spontaneously emit white light, Salisbury points out, but they’re not the first to report using quantum dots to produce hybrid, white-light LEDs.

“The other reports – one by a group at the University of St. Andrews in Scotland and one by a group at Sandia National Laboratories – describe achieving this effect by adding additional compounds that interact with the tiny crystals to produce a white-light spectrum,” he says.

“The magic-sized quantum dots, by contrast, produce white light without any extra chemical treatment: The full spectrum emission is an intrinsic effect.”

The report of the Vanderbilt discovery appears in White-light Emission from Magic-Sized Cadmium Selenide Nanocrystals published online on October 18 by the Journal of the American Chemical Society.

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See:-
Vanderbilt University - Quantum dots that produce white light could be the light bulb’s successor, October 20, 2005

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