New “non-blinking” nanocrystals promise increased efficiency in LED lighting

High-brightness LEDs lose about 17% of their energy due to quantum losses such as imperfections in the crystalline structure. Another source of quantum loss is due to an effect called “blinking.” A breakthrough nanocrystal, developed at the University of Rochester with help from Kodak and the Naval Research Lab, holds promise for eliminating losses due to blinking in LEDs which show up as heat, a bugbear of solid-state lighting designers.

Here’s a description of blinking, and how its reduction lowers quantum loses that would otherwise end up as heat:

“Many molecules, as well as crystals just a billionth of a meter in size, can absorb or radiate photons. But they also experience random periods when they absorb a photon, but instead of the photon radiating away, its energy is transformed into heat. These "dark" periods alternate with periods when the molecule can radiate normally, leading to the appearance of them turning on and off, or blinking.

"A nanocrystal that has just absorbed the energy from a photon has two choices to rid itself of the excess energy—emission of light or of heat," says Todd Krauss, professor of chemistry at the University of Rochester and lead author on the study. "If the nanocrystal emits that energy as heat, you’ve essentially lost that energy."

Why no blinking? Krauss and fellow researcher Alexander Efros from the Naval Research Laboratory conclude, “Normally, nanocrystals have a core of one semiconductor material wrapped in a protective shell of another, with a sharp boundary dividing the two. The new nanocrystal, however, has a continuous gradient from a core of cadmium and selenium to a shell of zinc and selenium. That gradient squelches the processes that prevent photons from radiating, and the result is a stream of emitted photons as steady as the stream of absorbed photons.”

If you’re watching current advances in HB LED technology you’re probably familiar with organic LEDs (OLEDs), those cheap, printable LEDs just beginning to find use in displays. The article quotes Krauss as referring to the new nanocrystal as being a possible successor to OLEDs, which have significant drawbacks, such as low lifetimes. Sounds like this nanocrystal technology could possibly leapfrog OLEDs.

This research is detailed in the current issue of Nature. [via Physorg.com]