Scientists growing new crystals to make LED lights useful for office, home

LEDs that emit a broad spectrum of warm white light on par with sunlight has proven tricky

When to comes to offering warm yet visually efficient lighting, LEDs have a long way to go.  But scientists with the University of Georgia and Oak Ridge and Argonne national laboratories are looking at  new family of crystals they say  glow different colors and hold the key for letting white LED light shine in homes and offices as well as natural sunlight.

According to the scientists, Light-emitting diodes, or LEDs, offer energy savings over incandescent and fluorescent lights and are easily produced in single colors such as red or green commonly used in traffic lights or toys.   However building an LED that emits a broad spectrum of warm white light on par with sunlight has proven tricky, the scientists said.

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Technically the LEDs produce light by passing electrons through a semiconductor material, in combination with materials called phosphors that glow when excited by radiation from the LED.  "But it's hard to get one phosphor that makes the broad range of colors needed to replicate the sun," said John Budai, a scientist in ORNL's Materials Science and Technology division in a release. "One approach to generating warm-white light is to hit a mixture of phosphors with ultraviolet radiation from an LED to stimulate many colors needed for white light."

The researchers have grown nanocrystals using europium oxide and aluminum oxide powders as the source materials because the rare-earth element europium is known to have good phosphorescent properties.

The group has been studying the atomic structure of the materials using x-rays from Argonne's Advanced Photon Source. Two of the three types of crystal structures in the group of phosphors had never been seen before, which can probably be attributed to the crystals' small size, Budai said.

Advancing the material's luminescence efficiency is key to making it useful for commercial LED products and other applications; the new nanocrystals may turn out to have other practical photonic uses beyond phosphors for LEDs. Their ability to act as miniature "light pipes" when the crystal quality is high enough could lend them to applications in fiber-optic technologies, Budai said.

The researchers didn't offer a timetable as to when this technology might end up lighting up your office or dining room.

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