Tuesday, July 9, 2013

New Phosphors could make LEDs To Shine More Like Natural Sun

LEDs are more efficient and have longer lifespan than incandescent and fluorescent lights. But technically it is still a challenge to make LED to produces warm, white light like sunlight. It turns out that creating phosphors that can emit a broad spectrum of wavelengths mimicking natural light is a tricky business.

Natural light composes spectrum from ultraviolet to infrared (250 nm to 1800 nm of wavelength). When ultraviolet photons generated from LED hit a phosphor, white light will be emitted. The problem is that the spectrum of this LED's white light isn't broad enough to mimic sunlight, as shown below.

Scientists from Oak Ridge and Argonne national labs and the University of Georgia, U.S.A., are working together to develop a new group of phosphors that glow in a broader part of the spectrum.

“It’s hard to get one phosphor that makes the broad range of colors needed to replicate the sun," said John Budai, an Oak Ridge materials scientist. “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."

They are growing and testing nanocrystals composed of europium oxide and aluminum oxide powders. Europium is a rare-earth element that has exceptional phosphorescent qualities, which glow in lots of different colors — some are orange, purple, green or yellow.

They are using X-rays to understand how atoms are arranged in the phosphorescent materials. Once they figure out how altering crystal growing conditions change the colors emitted, they hope to create lighting close to natural sunlight.

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