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The next generation light bulb: Magic-sized quantum dots



Fluorescent lamps today can already provide an average of 10,000
hours of use compared to the 750 hours of a incandescent bulb. Now, imagine a
next generation lamp that can provide an average of 50,000 hours of use. A
discovery at Vanderbuilt University
brought us a step closer. It is based on an already available technology, the light
emitting diodes (LED) which is already replacing incandescent and fluorescent
lights in applications like traffic lights, architectural lighting, flashlights,
reading lights and even in car lights. LEDs are still considerably more
expensive than ordinary lights but they are more resistant and durable. Until
1993 they could only produce red, green and yellow lights but new technologies like
color combination and quantum dots, are starting to bring other options like
blue and white LEDs. So far, these technologies were capable of creating a white
light with a bluish tinge.




Michael Bowers, a graduate student at Vanderbuilt
University, accidentally came to the solution by trying to create smaller and
smaller quantum dots which can be described as very small beads capable of
changing the light wavelength that excite them at the atomic level. By trying
to create them smaller, Bowers made a batch of the smallest quantum dots he
knew how to make composed of crystals of cadmium and selenium that contains
either 33 or 34 pairs of atoms. After cleaning up the batch, he dropped a
solution containing the nano-crystals into a small glass cell and illuminated
it with an ultraviolet laser beam. He was surprised to see the quantum dots emitting a
white glow with a smoother distribution of wavelengths (slightly more yellow
tint) similar to the traditional light bulbs. It turned out that these quantum
dots created were in a configuration called “magic size” because it is one of
the preferred forms of the crystal. The result is that this configuration of
quantum dots are easier to make and can lower the LED production cost.




Quantum dots have another very important characteristic: they
can not only change the wavelength of the light that hits them but they can also
produce light by applying an electrical current. These quantum dots can be
applied to any surface as a paint and enable these surfaces to act as a light
source. The future light bulb can, in fact, be a wall, a frame or even the
curtains. Vanderbuilt University
has this project of applying electrical current to the specific quantum dot
created by Michael Bowers at the top of the list.




The report of their discovery is in the communication “White-light
Emission from Magic-Sized Cadmium Selenide Nanocrystals” published by the
Journal of the American Chemical Society on October 18.





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