New Nanocrystalline Material Rapidly Converts Blue Laser Emission to White Light

A nanocrystal-based material converts blue laser emission to white light for combined illumination and data communication. (Photo credit: KAUST 2016)

A team of researchers from King Abdullah University of Science & Technology (KAUST) have created a nanocrystalline material that rapidly produces white light out of blue light.

Bluetooth and Wi-Fi are already proven technologies, but there are several benefits obtained by shortening the wavelength of the electromagnetic waves used to transmit data.

Visible-light communication (VLC) utilizes parts of the electromagnetic spectrum that are not regulated and potentially highly energy-efficient. VCL also provides a way to integrate data transmission with illumination and display technologies, for instance, using ceiling lights to supply internet connections to laptops.

Several VLC applications require LEDs that generate white light. These are often fabricated by integrating a diode that transmits blue light with phosphorous that coverts a portion of this radiation into green and red light. However, this conversion process is not fast enough to meet 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.

Boon Ooi, Professor of Electrical Engineering, KAUST

As an alternative, Ooi, Associate Professor Osman Bakr and their colleagues use a nanocrystal-based converter that facilitates much higher data rates.

The researchers developed nanocrystals of cesium lead bromide that were about 8nm in size using a simple and cost-effective solution-based technique that integrated a conventional nitride phosphor. When a blue laser light was used to illuminate, the nanocrystals emitted green light and the nitride emitted red light. Collectively these created a warm white light.

The team differentiated the material’s optical properties with a method called femtosecond transient spectroscopy. They could illustrate that the optical processes in cesium lead bromide nanocrystals take place on a time-scale of approximately seven nanoseconds.

This then made it possible for the optical emission to be modulated at a frequency of 491 MHz, which is 40 times faster than is achievable using phosphorus, and convey data at a rate of two billion bits per second.

The rapid response is partly due to the size of the crystals. Spatial confinement makes it more likely that the electron will recombine with a hole and emit a photon.

Osman Bakr, Associate Professor, KAUST

Significantly, the white light produced using their perovskite nanostructures was of a quality consistent with current 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.

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