Monday, November 14, 2005

"QUANTUM: dot technique builds 'better light bulb'"

Vanderbilt University researchers claim their quantum-dot approach to the generation of tunable broad-spectrum white light simplifies solid-state lighting. The quantum-dot light bulb, invented by professor Sandra Rosenthal uses a single size of nanocrystal to produce white light when irradiated with commercially available blue LEDs. The work shows that building a "better light bulb" does not require pumped lasers, exotically formulated phosphors or integrated quantum wells and nanocrystals, Rosenthal said: All you need to do is coat blue LEDs with her broad-spectrum quantum dots. The quantum-dot light bulbs are predicted to last as long as their LEDs-up to 50,000 hours, or 50 times as long as a normal light bulb. Usually the emitted light's wavelength is determined by the nanocrystal size-for example, a 10-nanometer diameter for red-but Rosenthal's group discovered a size and surface treatment combination that enables a single quantum dot to emit a full spectrum combination of light, resulting in warm yellowish white emission. The quantum dots used were half the size of normal nanocrystals and appeared to exhibit photonic surface emission. Rosenthal hopes that stimulating her photonic surface-emitting quantum dots electrically will yield an all-semiconductor white light bulb that does not rely on exotic compounds. The quantum dots theoretically could be sprayed on any surface to turn it into a light bulb producing a variable rainbow of shades.