This scientific breakthrough has potential applications in the development of lasers and sensors. Source: Jean Lachat

Scientists at the University of Chicago have demonstrated a way to create infrared light using colloidal quantum dots. Researchers say this method is very promising. Although the experiments are still early, the results are already as efficient as traditional methods.

These dots could one day form the basis of infrared lasers or small, inexpensive sensors such as those used in emissions tests or breathalyzers.

Philippe Guyot-Sionnest, a professor of physics and chemistry at the University of Chicago and one of the authors of the paper published in Nature Photonics, mentioned that the performance of these spots is similar to existing commercial infrared sources. He also expressed optimism that they can further improve this performance. “We’re very excited about the possibilities.”

suitable wavelength

Colloidal quantum dots are small crystals emitting various light colours based on size. They’re efficient, easy to make, and already used in commercial technology; you might have bought a quantum dot TV without knowing it.

However, these quantum dots are being used to create light at visible wavelengths – the part of the spectrum that humans can see. You’re missing out if you want quantum dot light at infrared wavelengths.

But infrared light has many uses. In particular, it is useful for making sensors. You can use infrared to check for harmful gases in your car’s exhaust, test your breath for alcohol levels, and ensure there’s no methane gas in your drilling equipment. This is because different types of molecules absorb specific wavelengths of infrared light, making them easy to distinguish.

“So a cost-effective and easy-to-use method of producing infrared light using quantum dots is very useful, according to graduate student Xingyu Shen, the study’s first author. Professors Philippe Guyot-Sionnest and Xingyu Shen conducted the research in their Gordon Center for Integrated Sciences laboratories at the University of Chicago. Source: Jean Lachat

Infrared lasers are now made through molecular epitaxy, which works well but requires a lot of labour and cost. Scientists think there may be another way.

Guyot-Sionnest and his team have been experimenting with quantum dot and infrared technologies for years. They wanted to use the “cascade” technique to create lasers with colloidal quantum dots, which had not been done before.

In this “cascade” technique, researchers apply an electric current to a device, causing millions of electrons to pass through it. If the device’s structure is correct, electrons will move through various energy levels, similar to falling down a series of waterfalls. Every time an electron drops down an energy level, it has a chance to release some energy in the form of light.

The researchers wanted to know if they could create the same effect with quantum dots. They created a black “ink” made of trillions of tiny nanocrystals, spread it on a surface, and passed an electric current through it.

“We thought it might work, but we were really surprised by how well it worked,” Guyot-Sionnest said. “From our first try, we saw the light.”

In fact, they found that this method was already as effective as other traditional methods of producing infrared light, even in exploratory experiments. With further improvements, the method could easily surpass existing methods, the scientists say.

Potential applications

They hope this discovery will significantly reduce the cost of infrared light and lasers, opening up new application areas.

“I think this is one of the best examples of the potential applications of quantum dots,” Guyot-Sionnest said. “Many other applications can be achieved with other materials, but this structure only works because of quantum mechanics. I think it’s advancing the field in a very interesting way.”

More information: Shen Xingyu et al., Mid-infrared cascade in-band electroluminescence of HgSe-CdSe core-shell colloidal quantum dots, Nature Photonics (2023). DOI: 10.1038/s41566-023-01270-5