Scientists have demonstrated a new way to make infrared light from quantum dots, and the experiments are still in the early stages

Scientists at the University of Chicago have demonstrated a way to create infrared light using colloidal quantum dots. The researchers say this approach shows great promise; Although the experiment is still in its early stages, these quantum dots are already as efficient as existing conventional methods.

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

"Currently, the performance of these quantum dots is close to that of existing commercial infrared light sources, and we believe we can significantly improve this," says Philippe Guyot-Sionnest, co-author of the study published in Nature Photonics. One of the three authors on the paper.

Suitable wavelength

Colloidal quantum dots are tiny crystals - you could fit a billion crystals at the end of this sentence - and they will emit different colors of light, depending on how big you make them. They are highly efficient, easy to manufacture and are already used in commercial technology; You may have already bought a quantum dot TV and not know it.

However, these quantum dots are being used to make light at visible wavelengths - the part of the spectrum that humans can see. If you want quantum-dot light at infrared wavelengths, you're making a big mistake.

But infrared light has many uses. In particular, it's very useful for making sensors. For example, if you want to know if there are harmful gases in your car's exhaust, or test if you are breathing over the legal alcohol limit, or make sure there is no methane gas in your drilling equipment, you can use infrared. That's because different types of molecules absorb specific wavelengths of infrared light, so they're easy to tell apart.

Infrared lasers are now manufactured by a method called molecular epitaxy, which works well but requires a lot of labor and cost. Scientists think there may be another way.

Guyot-Sionnest and his team have been experimenting with quantum dots and infrared technology for years. Building on their previous invention, they set out to try to recreate a "cascade" technique that has been widely used to make lasers but has never been achieved on colloidal quantum dots.

In this "cascade" technique, researchers apply an electric current to the device, sending millions of electrons through the device. If the structure of the device is just right, the electrons will pass through a series of different energy levels, as if falling down a series of waterfalls. Every time an electron drops an energy level, it has a chance to release some of its energy in the form of light.

The researchers wondered if they could create the same effect with quantum dots. They created a black "ink" made up of trillions of tiny nanocrystals, spread it on a surface, and let an electric current pass through it.

"We thought it might work, but we were really surprised at how well it worked," Guyot-Sionnest said. "From our first attempt, we saw the light."

In fact, they found that this method is already as effective as other traditional methods of generating infrared light, even in exploratory experiments. The scientists say that with further improvements, the method could easily outperform existing methods.

Potential application

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

"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 really only works because of quantum mechanics." I think it's moving the field forward in a really interesting way."

Source: Chinese Optical Journal Network