In a report published May 10, 2006, in the research journal Nano Letters, Foreman, Everitt, Liu and co-researchers first disclosed they could induce a formulation of zinc oxide shaped into nanowires to absorb light from an ultraviolet laser and re-emit it as a "broadband visible emission of unprecedented brightness." The white light component was more than 1,000 times brighter than the ultraviolet component, they reported.
In a followup report, published July 2, 2007, in the journal Applied Physics Letters, the Duke researchers initiated what they expect to be a series of published papers exploring how various alterations affect the white light emissions.
"We've learned something about what makes the white light conversion happen, and what makes it happen so efficiently," Everitt said. The Duke team has already achieved efficiencies as high as 80 percent. But there are still technical issues to resolve tied to the operating temperatures of the phosphors and the power from the underlying ultraviolet LED.
"Our challenge has been getting a foundational understanding so we can understand what is physically possible and how close we are to achieving it," Everitt said.
Zinc oxide would be both a less-toxic and cheaper light source than the combinations used in today's commercial LEDs -- gallium nitride and cerium-doped yttrium oxide, they said. Cerium-doped yttrium oxide is also used in today's mercury-containing fluorescent bulbs, Everitt added.
Liu's lab originally stumbled on to the light emitting potential of sulfur-doped zinc oxide while studying its electronic conductivity. "We just lit it up with an ultraviolet laser and -- whammo -- there was a lot of white light coming out," Everitt said.
|Contact: Monte Basgall|