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Melbourne Uni Develops New LED Technology

Your smart device could soon be even smarter with a new infrared light-emitting diode (LED) that is ‘tuneable’ to different wavelengths of light – it could enable your fridge to tell you when your food is going off and your phone to tell you if that Gucci purse is real.

The technology has been developed by the University of Melbourne, the Lawrence Berkeley National Laboratory, the University of California, Berkeley, and the Australian Research Council Centre of Excellence for Transformative Meta-Optical Systems (TMOS). They have come up with a device that could identify a suite of gases, potentially including lethal ones, improving the safety of firefighters, miners, the military, and your local plumber. The work appeared in the journal, Nature.

Infrared (IR) spectrometers are common laboratory equipment that can identify different materials by analysing their infrared signatures, which is invisible to the human eye. Just like an AM radio can be tuned to different frequencies of radio waves, IR spectrometers can be tuned to different wavelengths, giving a broad-spectrum analysis of a gas sample. However, these machines are bulky and expensive and not usually practical to take out of the laboratory and into the field.

University of Melbourne Professor Kenneth Crozier said that the team’s new technology bonds a thin layer of black phosphorus crystals to a flexible, plastic-like substrate, allowing it to be bent in ways that cause the black phosphorus to emit light of different wavelengths essentially creating a tuneable infrared LED that allows for the detection of multiple materials. He noted that this technology could fit inside smartphones and become part of everyday use.

For example, the bacteria found in meat release various gases as they multiply. The presence of these gases is a good indication that the meat is spoiling and is no longer fit for consumption.

Professor Crozier, who is also the Deputy Director of TMOS, noted that the device placed inside a fridge could send a notification that meat is going off. When pointed at a handbag, it could reveal whether the bag is made of real leather or a cheaper substitute.

Current materials that are used for IR photodetectors and light-emitting devices can be difficult to manufacture, in large part due to the need for multiple layers of perfectly linked crystals. This new black phosphorus technology requires just one layer allowing the device to be flexible, giving it unique properties when bent.

Professor Ali Javey, from the University of California at Berkeley, whose group led the work stated that the shift in black phosphorus’ emission wavelength with bending is quite dramatic, enabling the LED to be tuned across the mid-infrared.

Importantly, the device could make the work of firefighters, miners and military safer, allowing them to identify potentially lethal gases from safe distances as the ultra-thin, ultra-light devices can be placed on small drones. Flying such a drone over a building fire could tell firefighters what dangers they face and the equipment they’ll need.

The low-cost technology could also make its way into devices for use by plumbers and building managers.

“Our IR photodetectors could be integrated into a camera so that we could look at our phone screen and ‘see’ gas leaks or emissions and be able to determine what kind of gas it is,” Professor Crozier said.

In the research, the team demonstrates high-performance room-temperature infrared optoelectronics with actively variable spectra by presenting black phosphorus as an ideal candidate. Enabled by the highly strain-sensitive nature of its bandgap, which varies from 0.22 to 0.53 electronvolts, they show a continuous and reversible tuning of the operating wavelengths in light-emitting diodes and photodetectors composed of black phosphorus.

Furthermore, they leverage the platform to demonstrate multiplexed nondispersive infrared gas sensing, whereby multiple gases (for example, carbon dioxide, methane and water vapour) are detected using a single light source.

With its active spectral tunability, while also retaining high performance, the work bridges a technological gap, presenting a potential way of meeting different requirements for emission and detection spectra in optoelectronic applications.

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