Volume 91 Issue 5 | p. 8 | News of The Week
Issue Date: February 4, 2013 | Web Date: January 31, 2013

LEDs Made From Silicon Quantum Dots Shine In New Colors

Nanotechnology: The silicon devices could serve as an alternative to light-emitting diodes based on toxic metals
Department: Science & Technology
News Channels: Materials SCENE, Nano SCENE
Keywords: quantum dot LEDs, QLEDs, silicon quantum dots, displays
Silicon quantum dots glow different colors depending on the size of the nanocrystals.
Credit: Nano Lett.
This is a photo of silicon quantum dots in toluene that glow different colors based on the size of the nanocrystals.
Silicon quantum dots glow different colors depending on the size of the nanocrystals.
Credit: Nano Lett.

Quantum dots, semiconducting inorganic nanocrystals, have unique properties, such as the ability to emit pure colors, that could make them ideal as the basis for light-emitting diodes in computers and television displays.

Unfortunately, quantum dot LEDs often rely on toxic heavy metals such as cadmium to emit light. Now, researchers report new colors of LEDs that use silicon quantum dots.

Silicon could be a less toxic alternative, but scientists have struggled to fabricate silicon-based devices that glow in colors across the visible spectrum. Current silicon LEDs emit only red and near-infrared light.

That’s because researchers haven’t controlled the sizes of the silicon quantum dots in their devices, say Uli Lemmer of Karlsruhe Institute of Technology, in Germany, and Geoffrey A. Ozin of the University of Toronto.

To control the sizes of the nanocrystals, Lemmer, Ozin, and their colleagues report separating quantum dots by ultracentrifugation, a technique often used to isolate biomolecules. After synthesizing silicon quantum dots by a previously reported method, the team spun a solution of 1- to 3-nm-diameter nanocrystals in a high-speed centrifuge. The spinning separated the quantum dots into 30 groups; within each group, particles had the same size.

The researchers then took crystals of the same size and fabricated LEDs by spreading a layer of the quantum dots between two electrodes. The wavelength of light emitted by the LEDs increased with the size of the quantum dots. For instance, LEDs with 1.3-nm-diameter particles glowed yellow, while devices with 1.8-nm crystals glowed red (Nano Lett., DOI: 10.1021/nl3038689).

Lemmer and Ozin say they next need to improve the devices’ efficiency at converting electricity into light.

Russell J. Holmes of the University of Minnesota, Twin Cities, thinks sorting quantum dots by size will be crucial if silicon quantum dot LEDs are to gain widespread application. But he says the ultimate challenge for scientists will be producing green and blue devices, which require synthesis of small silicon quantum dots.

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