Technology.am (May 11, 2009) — Now scientists have created a nanocrystal that constantly emits light. It could be less expensive and more versatile lasers, brighter LED lighting, and biological markers that track how a drug interact with a cell at a level never before possible.
University of Rochester scientists along with researchers at the Eastman Kodak Company have discovered continuously emitting light sources from individual molecules.
They said, many molecules, as well as crystals just a billionth of a meter in size, can absorb or radiate photons. But they also experience random periods when they absorb a photon, but instead of the photon radiating away, its energy is transformed into heat. These “dark” periods alternate with periods when the molecule can radiate normally, leading to the appearance of them turning on and off, or blinking.
“A nanocrystal that has just absorbed the energy from a photon has two choices to rid itself of the excess energy—emission of light or of heat,” says Todd Krauss, professor of chemistry at the University of Rochester. “If the nanocrystal emits that energy as heat, you’ve essentially lost that energy.”
Krauss and Keith Kahen scientist of Kodak were exploring new types of low-cost lighting similar to organic light-emitting diodes, but which might not suffer from the short lifespans and manufacturing challenges inherent in these diodes.
Kahen synthesized nanocrystals of various compositions. After an investigation, they concluded that the reason the blinking didn’t occur was due to the unusual structure of the nanocrystal.
Normally, nanocrystals have a core of one semiconductor material wrapped in a protective shell of another, with a sharp boundary dividing the two.
The new nanocrystal, however, has a continuous gradient from a core of cadmium and selenium to a shell of zinc and selenium. That gradient squelches the processes that prevent photons from radiating, and the result is a stream of emitted photons as steady as the stream of absorbed photons.
With blink-free nanocrystals, Krauss believes lasers and lighting could be incredibly cheap and easy to fabricate.
Currently, different color laser light is created using different materials and processes, but with the new nanocrystals a single fabrication process can create any color laser. To alter the light color, an engineer needs only to alter the size of the nanocrystal.
Krauss says one day it could be the successor of OLED. A grid of differently sized nanocrystals onto a flat surface could create computer displays as thin as paper, or a wall that lights a room in any desired color.