An inexpensive and safe sunburn and diaper rash preventative can help produce brilliant light that is good for the human eye, according to researchers.
Led by Duke adjunct physics professor Henry Everitt, the researchers found 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.
AdvertisementAnd now, the researchers are working towards creating an optimal design for a new kind of illumination. Already, the scientists 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.
The researchers said they are producing white light centred in the green part of the spectrum by forming the sulphur-doped preparation into a material called a phosphor, which converts the excited frequencies from an ultraviolet light emitting diode (LED) into glowing white light.
The researchers are preparing Nanometer-diameter zinc oxide powders, which are then being tested at the Aviation and Missile Research, Development and Engineering Centre at Redstone Arsenal by Everitt.
Also, they are exploring using electricity alone to trigger the visible emissions without need for an ultraviolet light trigger.
"One of the objectives is to give soldiers efficient lighting that doesn't run their batteries down. They need efficiency, brightness, longevity and ruggedness, and this helps with all of those things," said Everitt.
He added that existing commercial LEDs are already rugged enough to be used in bumper-mounted brake lights. Also, white LEDs on the market now are costly, short-lived and not truly white.
"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," said chemistry professor Jie Liu.
A compound that can be used on faces or babies' bottoms also has major safety advantages over fluorescent bulbs, which happen to contain toxic mercury.
It's known since long that zinc oxide can itself serve as a solid state ultraviolet light source. Also, scientists have known that adding sulfur allows it to emit some white light.
But the researchers are investigating how nanostructuring and doping improves its performance.
The introduced sulfur is thought to boost wavelength conversions from ultraviolet to visible wavelengths by serving as an "impurity" that changes the chemistry and physics of the zinc oxide in ways the Duke researchers are still probing.
They said that while most scientists consider such impurities "defects" that interfere with zinc oxide's ability to produce a stronger ultraviolet light.
But "we love the defects that other people hate. That's been the gift of nanostructured doped zinc oxide, emitting what your eye expects white light to look like. We've learned something about what makes the white light conversion happen, and what makes it happen so efficiently," said Everitt.
The Duke team has already achieved efficiencies as high as 80 percent.
The researchers 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," said Everitt.
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