White Light for Faster Communication

A nanocrystal-based material converts blue laser emission to white light for combined illumination and data communication (Source: KAUST)

A nanocrystal-based material converts blue laser emission to white light for combined illumination and data communication (Source: KAUST)

A nano­crystalline material that rapidly makes white light out of blue light has been developed by researchers at King Abdullah University of Science and Techno­logy KAUST. While Wi-Fi and Bluetooth are now well established techno­logies, there are several advantages gained by shortening the wavelength of the electro­magnetic waves used for trans­mitting information. Visible-light commu­nication (VLC) makes use of parts of the electro­magnetic spectrum that are unre­gulated and is potentially more energy-efficient. VCL also offers a way to combine information trans­mission with illu­mination and display techno­logies, for example, using ceiling lights to provide internet connec­tions to laptops.

Many such VLC appli­cations require light-emitting diodes (LEDs) that produce white light. These are usually fabricated by combining a diode that emits blue light with phos­phorous that turns some of this radiation into red and green light. However, this conversion process is not fast enough to match the speed at which the LED can be switched on and off. “VLC using white light generated in this way is limited to about one hundred million bits per second,” said KAUST Professor of Electrical Engi­neering Boon Ooi. Instead, Ooi and their colleagues use a nano­crystal-based converter that enables much higher data rates.

The team created nano­crystals of cesium lead bromide that were roughly eight nanometers in size using a simple and cost-effective solution-based method that incor­porated a con­ventional nitride phosphor. When illuminated by a blue laser light, the nano­crystals emitted green light while the nitride emitted red light. Together, these combined to create a warm white light.

The researchers charac­terized the optical properties of their material using a technique known as femto­second transient spectros­copy. They were able to show that the optical processes in cesium lead bromide nano­crystals occur on a time-scale of roughly seven nano­seconds. This meant they could modulate the optical emission at a frequency of 491 Megahertz, 40 times faster than is possible using phos­phorus, and transmit data at a rate of two billion bits per second.

“The rapid response is partly due to the size of the crystals,” said Bakr. “Spatial con­finement makes it more likely that the electron will recombine with a hole and emit a photon.” Impor­tantly, the white light generated using their perovskite nano­structures was of a quality comparable to present LED techno­logy. “We believe that white light generated using semi­conductor lasers will one day replace the LED white-light bulbs for energy-ef­ficient lighting,” said Ooi. (Source: KAUST)

Reference: I. Dursun et al.: Perovskite Nanocrystals as a Color Converter for Visible Light Communication, ACS Phot. 3, 1150 (2016); DOI: 10.1021/acsphotonics.6b00187

Link: Photonics Laboratory, Computer, Electrical, and Mathematical Sciences and Engineering CEMSE, King Abdullah University of Science and Technology KAUST, Thuwal, Saudi Arabia

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