Duke adjunct physics professor Henry Everitt, chemistry professor Jie Liu and their graduate student John Foreman have discovered that adding sulfur to ultra-fine powders of commonplace zinc oxide at about 1,000 degrees centigrade allows the preparation to convert invisible ultraviolet light into a remarkably bright and natural form of white light.
They are now probing the solid state chemistry and physics of various combinations of those ingredients to deduce an optimal design for a new kind of illumination. Everitt and Liu have applied for a patent on using the preparations as a light source. "Our target would be to help make solid state lighting with better characteristics than current fluorescent ones," said Everitt, who also works with Foreman at the Army's Redstone Arsenal in Huntsville, Ala.
The researchers said they are producing white light centered in the green part of the spectrum by forming the sulfur-doped preparation into a material called a phosphor. The phosphor converts the excited frequencies from an ultraviolet light emitting diode (LED) into glowing white light.
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.
More at The Bright White Light article from Science Daily.