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Oct. 9, 2003 – Quantum dots have been shining light on cell biology for years. Now scientists at Sandia National Laboratories want them to shine on us as an energy-efficient alternative to incandescent and fluorescent lights.
Lauren Rohwer and her colleagues in Albuquerque, N.M., developed encapsulated nanocrystals that can be integrated onto commercially available light-emitting diode (LED) chips to produce white light. Dubbed quantum dots, the nanocrystals absorb invisible light from the LED and emit it as white light.
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“It’s the first demonstration, to our knowledge, of a real solid-state source that uses quantum dots,” said Rohwer, the lead investigator. “White is the biggest accomplishment.”
Quantum dots are nanoscale semiconductor crystals that absorb and emit photons of light at specific light waves, from visible colors into infrared. The size of the dot determines which color, or wavelength, is absorbed. Quantum dots often are used in the life sciences as cellular tags that track biological molecules such as DNA in a cell.
White light is actually a mixture of colors, and getting the right combination using quantum dots is a difficult task. Rowher and her colleagues found that size is not the only method for controlling optical properties, though. They discovered that interactions between the nanocrystal clusters and materials they can be embedded in can affect the color emitted.
But the process of encapsulating quantum dots is tricky. First the group had to devise an inexpensive method for making the nanocrystals at room temperature, and disperse them evenly. An encapsulating polymer was designed as a backbone on which the dots could be attached. Without the polymer, the nanocrystals would clump up and lose their emissive properties.
Quantum dots are an attractive alternative to conventional lighting sources because they are efficient. Nanocrystals are smaller than waves of light, so unlike the much larger phosphors used in conventional lighting, they don’t scatter light waves. Scattering can reduce optical efficiency by as much as 50 percent.
The Department of Energy estimates that lighting accounts for more than 20 percent of electricity used in the nation. Increased efficiencies could reduce demand, which in turn would lower costs and take some burden off the grid.