Scientists demonstrate a new and improved method for producing infrared light using quantum dots

Scientists from the University of Chicago have demonstrated a way to create infrared light using colloidal quantum dots. The researchers said the method shows great promise. The points are already as effective as current conventional methods, although the trials are still in their infancy.

The dots could one day form the basis of infrared lasers as well as small, cost-effective sensors, such as those used in exhaust emissions tests or alcohol analyzers.

“Right now, the performance of these points is close to that of existing commercial infrared sources, and we have reason to believe we can improve that significantly,” said Philippe Joyo-Sionest, a professor of physics and chemistry at the University of Chicago and a member of the research team. James Frank Institute, and one of three authors on the paper published in Nature photonics. “We are very excited about the possibilities.”

correct wavelength

Colloidal quantum dots are tiny crystals — you could insert a billion of them in the period at the end of this sentence — that emit different colors of light depending on their size. It is highly effective, easy to make, and is already being used in commercial technology; You may have already purchased a quantum dot TV without even knowing it.

However, those quantum dots are used to emit light in the visible wavelength, which is the part of the spectrum that humans can see. If you want quantum dot light in the infrared wavelength, you’re probably out of luck.

But infrared has many uses. In particular, it is very useful for making sensors. If you want to see if harmful gases are coming out of your car’s exhaust, test if your breath is above the legal alcohol limit, or make sure no methane is coming out of your drilling station, for example, you can use an infrared light. This is because different types of molecules will each absorb infrared light at a very specific wavelength, so it is easy to tell them apart.

“So a cost-effective and easy-to-use method for producing infrared light using quantum dots can be very useful,” explained Xingyu Chen, a graduate student and first author of the new study.

Infrared lasers are now being manufactured by a method called molecular epitaxy, which works well but is labor and cost intensive. Scientists thought there might be another way.

Guyot-Sionest and his team have been experimenting with quantum dots and infrared technology for years. Building on their previous inventions, they set out to attempt to recreate the “cascade” technology that is widely used to make lasers, but has never been achieved with colloidal quantum dots.

In this “cascade” technique, researchers run an electric current through a device, sending millions of electrons traveling through it. If the structure of the device is just right, the electrons will travel through a series of distinct energy levels, like falling down a series of cascades. Each time an electron descends to an energy level, it has the opportunity to emit some of that energy in the form of light.

The researchers wondered if they could create the same effect using quantum dots. They made black “ink” made of trillions of tiny nanocrystals, spread it on a surface and sent an electric current through it.

“We thought it was more likely to work, but we were really surprised by how well it worked,” Guyot-Sionest said. “Immediately, from the first time we tried it, we saw the light.”

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

potential applications

They hope this discovery will lead to much cheaper lamps and lasers, which could open up new applications.

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