Researchers at the U.S. Department of Energy's Los Alamos National Laboratory in Los Alamos, N.M., and the Massachusetts Institute of Technology in Cambridge have demonstrated that nanoscale semiconductor particles efficiently emit laser light. Known as nanocrystal quantum dots, the particles may lead to novel optical and optoelectronic devices, including tunable lasers, optical amplifiers, and light-emitting diodes.
These experimental dots are so small, quantum mechanical effects control their behavior. Much like other semiconductor lasers, quantum-dot lasers manipulate a material into a high-energy state before converting it to a low-energy state. This yields the net release of energy emitted in photon form.
One main challenge in manipulating quantum dots is that competing mechanisms emit energy in different forms, including vibrational energy and electron kinetic energy. Since electrons in quantum dots are closely confined within a small volume, they are forced to strongly interact with one another. These interactions may cause the deactivation of the quantum dot through the Auger process. When this occurs, the emission of a photon is prevented.
Quantum dots exhibit sufficiently large optical gain for stimulated emission to overcome the nonradiative Auger process. Such stimulated emission, or lasing, is possible only when the dots in the sample are densely packed. This optimal behavior of quantum dots exists over a range of temperatures. Since the emission wavelength of a quantum dot is a function of its size, scientists can easily create light of various colors.
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