N.M. — A wireless nanodevice that functions like a
fluorescent light — but potentially far more efficiently
— has been developed in a joint project between the
National Nuclear Security Administration’s Los Alamos
and Sandia national laboratories.
experimental success, reported in the June 10 issue
of Nature, efficiently causes nanocrystals to emit
light when placed on top of a nearby energy source,
eliminating the need to put wires directly on the
energy source is a so-called quantum well that emits
energy at wavelengths most easily absorbable by the
efficiency of the energy transfer from the quantum
well to the nanocrystals was approximately 55 percent
— although in theory nearly 100 percent transfer of
the energy is possible and might be achieved with
work is another step in creating more efficient white-light-emitting
diodes — semiconductor-based structures more efficient
and hardier than the common tungsten light bulb.
of lighting costs is of wide interest because on a
world scale, lighting uses more electrical energy
per year than any other human invention.
pumped by quantum wells generate light in a process
similar to the light generation in a fluorescent light
a captive gas permeated by electricity emits ultraviolet
light that strikes the phosphor-coated surface of
the bulb, causing the coat to emit its familiar, overly
white fluorescent light.
current work shows that the nanocrystals can be pumped
very efficiently by a peculiar kind of energy transfer
that does not require radiation in the usual sense.
The process is so efficient, reports Los Alamos National
Laboratory (LANL) researcher Marc Achermann, because
unlike the fluorescent bulb, which must radiate its
ultraviolet energy to the phosphor, the quantum well
delivers its ultraviolet energy to the nanocrystal
very rapidly before radiation occurs.
the emissions of nanocrystals (a.k.a. quantum dots)
can be varied merely by controlling the size of the
dot rather than by the standard, cumbersome process
of varying the mix of materials, no known theoretical
or practical barriers exist to pumping different-sized
quantum dots that could individually emit blue, green,
or red light, or be combined to generate white light.
quantum well, about three nanometers thick, is composed
of a dozen atomic layers. It coats a wafer two inches
in diameter and is composed of indium gallium nitride.
The film is not fabricated but rather grown as crystal,
with an energy gap between its different layers that
emits energy in the ultraviolet range at approximately
this proof-of-principle work, the energy in the quantum
well was delivered with a laser. Although the difficulties
of inserting energy into the quantum well using an
electrical connection rather than laser light are
significant, it is considered to be feasible.
thin-film quantum well crystal film was grown at Sandia
by chemist Daniel Koleske.
role was small,” jokes Daniel, “but they couldn’t
have done it without me.”
researchers are reputed to be among the finest epitaxial
crystal-growers in the world.
researchers Achermann, Melissa Petruska, Simon Kos,
Darryl Smith, and Victor Klimov attached the semiconductor
nanocrystals, made the measurements, and created the
Sandia is a multiprogram laboratory operated by Sandia
Corporation, a Lockheed Martin company, for the U.S.
Department of Energy’s National Nuclear Security Administration.
Sandia has major R&D responsibilities in national
security, energy and environmental technologies, and
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