Bright, bendable light-emitting diodes.

The flex in this light-emitting diode (LED) marks the latest advance in harnessing electroluminescent polymers for billboards, electronic displays and uses not yet imagined.

Earlier this year, British scientists chemically modified polymers so that the materials glowed in a range of colors (SN: 3/14/92, p.164). Now, Goran Gustafsson and his colleagues at UNIAX Corp. in Santa Barbara, Calif., have gotten rid of the stiff metallic electrodes typically used to excite the polymer so that it gives off light. In the June 11 NATURE, they describe a completely plastic LED that they can curl or bend in half without disrupting its properties.

The group used a very thin layer of calcium and a soluble conducting polymer called polyaniline as electrodes. "The true breakthrough is that we can process polyaniline in the conducting form," says UNIAX President Alan J. Heeger. "It's like a liquid metal." This enables the researchers to use a technique called spin-casting to make flexible,more efficient light-emitting devices. They also mounted the electrodes and the luminescing semiconducting polymer on a transparent polymer film.

The new LED's light glows about twice as brightly as a television set, Heeger says. The light turns on with about 3 volts, making this LED compatible with existing digital devices. Next, the researchers hope to improve the device's long-term stability by replacing the calcium electrode with a less reactive material.