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Caged Atoms Offer Big Possibilities

Photonics Spectra
Oct 2000
Daniel S. Burgess

A technique that traps single atoms for study at room temperature may find applications in dense optical storage media, single-atom lasers and novel detectors. By doping nanocrystals with rare-earth ions, researchers are discovering phenomena that will benefit our understanding of matter and may lead to new materials.

A team from Oak Ridge National Laboratory and Nanocrystals Technology of Briarcliff, N.Y., has examined 2- to 10-nm-diameter Y2O3 particles, each of which cages a single europium ion. The researchers found that the crystals blink randomly at three well-defined intensity levels when they are exposed to laser light. Blinking has been documented in fluorescent molecules and in quantum dots, but, until now, it had always been observed as a binary, on/off phenomenon.

The nanocrystals were prepared using a proprietary chemical precipitation technique, said Ramesh N. Bhargava, founder and president of Nanocrystals Technology, which supplied the samples. The researchers illuminated the particles with 514.5-nm light from a low-power argon-ion laser. They collected 610- to 630-nm luminescence with an NA-0.85 objective on an inverted microscope from Nikon Inc. of Melville, N.Y., and detected it with a high-speed frame-transfer CCD camera from Princeton Instruments Inc. of Trenton, N.J.

The ability to study atoms at room temperature using standard microscopy is important in itself. The researchers, however, are already looking ahead toward more practical applications.

Efficient storage media for computing and for multimedia applications spring immediately to mind. Europium-doped nanocrystals could be used as nanoscale optical data storage units capable of storing four bits in a single element, said Michael D. Barnes, a staff scientist at the lab and member of the research team. "The main issue ... is the ability to externally control which state is accessed and its persistence time." He said the researchers are investigating the mechanism behind the blinking, with the hope that they can learn to manipulate it.
The applications, however, are wide open. Bhargava noted that the nano-particles display high quantum efficiency, making them suitable for use in sensors and displays, and as biotags and quantum-dot lasers. He said that, while research into the blinking phenomenon is still in its infancy, the company is looking into various applications.

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