Boffins switch on super-bright quantum dots

Researchers have set a record for the brightness of quantum dots that could be used in applications including LEDs, optical switches and personalised high-sensitivity biosensors.

The University of Illinois team placed quantum dots on a specially designed photonic crystal, and demonstrated that it could enhance fluorescence intensity by a factor of up to 108.

A quantum dot is a tiny piece of semiconductor material 2nm to 10nm in diameter (a nanometre is one billionth of a metre). When illuminated with invisible ultraviolet light, a quantum dot will fluoresce with visible light.

"We are using photonic crystals in a new way," said Brian Cunningham, a professor of electrical and computer engineering and corresponding author of a paper published in the August issue of the journal Nature Nanotechnology.

"We tune them to the specific wavelength of a laser used to stimulate the quantum dots, which couples the energy more efficiently and increases the brightness."

To enhance the fluorescence, Cunningham and his colleagues began by creating plastic sheets of photonic crystal using a technique called replica moulding. They then fastened commercially available quantum dots to the surface of the plastic.

"We designed the photonic crystal to efficiently capture the light from an ultraviolet laser and to concentrate its intensity right within the surface where the quantum dots are located," said Cunningham.