Duke University and United States Army scientists have found that a cheap and nontoxic sunburn and diaper rash preventative can be made to produce brilliant light best suited to the human eye.
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.
Nanometer-diameter zinc oxide powders are being prepared by Liu’s research group, which focuses on the chemistry of nanomaterials. He is Duke’s Jerry G. and Patricia Crawford Hubbard Professor of Chemistry. They are then being tested at the Aviation and Missile Research, Development and Engineering Center at Redstone Arsenal by Everitt, an Army senior research scientist, and Foreman, an Army research physicist.
The researchers are also exploring using electricity alone to trigger the visible emissions without need for an ultraviolet light trigger.
The Army has selected the project for priority funding through a competitive In-house Laboratory Independent Research program because of its potential advantages as an energy efficient and safe illumination source.
“One of the objectives is to give soldiers efficient lighting that doesn’t run their batteries down,” Everitt said. “They need efficiency, brightness, longevity and ruggedness, and this helps with all of those things.”
Existing commercial LEDs are already rugged enough to be used in bumper-mounted brake lights, Everitt said.
“They are good enough for decoration and for use in traffic lights, but they don’t make good reading lights because they are not of a white color that our eyes use best,” Liu said. White LEDs on the market now are costly, short-lived and not truly white, the researchers added. … – sd