Light is more or less useful at different
Researchers from Sandia National Laboratories have found a way to
make a tungsten photonic crystal emit 1.5 micron lightwaves, which are in
the near-infrared, or heat range. This makes it useful for thermal photovoltaic
devices, which turn heat into electricity.
The device absorbs a broad range of infrared wavelengths and converts
many of them to the 1.5 micron wavelength useful for photovoltaic devices.
It should also be possible to make the metal emit at the 0.5 micron
wavelength needed to use it as a light source, according to the researchers.
Photonic crystals are porous structures made by stacking rods or
boring a series of holes into a solid. The researchers' crystal is made
from rods of tungsten that measure one half micron in diameter, or about
150 times thinner than a human hair. The structure converts longer wavelengths
to shorter ones.
Photovoltaic devices made from the crystal could convert as much
as 34 percent of the light energy they take in into electricity, according
to the researchers.
The method could be used in electric motors in two to five years,
and for lighting in five to ten years, according to a Sandia spokesperson.
The work appeared in the July 14, 2003 issue of Applied Physics Letters.
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