Paris:

Quantum dots are tiny crystals that scientists can tune to different colours, giving an extra-vivid pop to next-generation TV screens or illuminating tumours inside bodies so surgeons can hunt them down. Three scientists won the Nobel Chemistry Prize on Wednesday for their work turning an idea first theorised in the 1930s into a reality that now has pride of place in living rooms across the world.

What are quantum dots?

Quantum dots are semiconducting particles just one-thousandth the width of a human hair. In 1937, the physicist Herbert Froehlich predicted that once particles were small enough — so-called nanoparticles — they would come under the strange spell of quantum mechanics.

To explain this quantum phenomenon, American Chemical Society president Judith Giordan said to “think of it like a little box”.

When a particle is shrunk down small enough, the electron is “going to whack into the sides of the box,” she told AFP.

In a larger box, the electrons would whack the sides less often, meaning they have less energy.

For quantum dots, the larger boxes emit red light, while the smaller ones show up blue.

This means that by controlling the size of the particle, scientists can make their crystals red, blue and everything in between.

Leah Frenette, an expert on quantum dots at Imperial College London, told AFP that working with the nanomaterial was like “watching rainbows all day”. 

But it would be 40 years after Froehlich’s prediction that anyone was able to actually observe this phenomenon.

In the early 1980s, Russian-born physicist Alexei Ekimov — one of Wednesday’s new laureates — melted coloured glass and X-rayed the results. 

He noticed that the smaller particles were more blue, also recognising that this was a quantum effect.

But being glass, the material was not easy to manipulate — and being published in a Soviet scientific journal meant few noticed.

At around the same time in the United States, another new laureate Louis Brus — oblivious of Ekimov’s work — became the first to discover this colourful quantum effect in a liquid solution.

“For a long time, nobody thought you could ever actually make such small particles, yet this year’s laureates succeeded,” Nobel Committee member Johan Aqvist said.

“However, for quantum dots to become really useful, you needed to be able to make them in solution with exquisite control of their size and surface.”

The third new Nobel winner, French-born Moungi Bawendi, found a way to do just this in his lab at the Massachusetts Institute of Technology in 1993.

By precisely controlling the temperature of a liquid mixture of particles called colloids, Bawendi was able to grow nanocrystals to the exact size he wanted, paving the way for mass production.

What are quantum dots used in?

The most common everyday use of quantum dots is probably in “QLED” televisions.

Cyril Aymonier, head of France’s Institute of Condensed Matter Chemistry, told AFP that the nanocrystals “improve the resolution of the screen and preserve the quality of the colour for longer”.

Doctors also use their bright fluorescence to highlight organs or tumours in the bodies of patients.

Frenette said she is working on diagnostic tests which would use the dots as “little beacons” for diseases in medical samples. 

One problem is that most quantum dots are made using cadmium, a toxic heavy metal.

Both Aymonier and Frenette said they are working on quantum dots that are not toxic.

What’s quantum dots’ future use?

In the future, quantum dots could have the potential to double the efficiency of solar cells, Giordan said.

Their strange quantum powers could produce twice as many electrons as existing technology, she explained.

“That’s amazing because we are coming closer to the limit of current solar materials,” she added.

Were quantum dots used in the past?

While quantum dots are considered on the cutting edge of science, people have probably been using them for centuries without knowing it.

The reds and yellows in stained glass windows as far as back as the 10th-century show that artists of the time unwittingly took advantage of techniques that resulted in quantum dots, according to scientists.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

Winners of the 2023 Nobel Prize in Chemistry on the screen: scientists Moungi Bawendi, Louis Brus and Alexi Ekimov, for discovery and synthesis of quantum dots.
| Photo Credit: AP/Claudio Bresciani

The story so far: The 2023 Nobel Prize in chemistry was awarded to Moungi G. Bawendi, Louis E. Brus and Alexei I. Ekimov on Wednesday for the discovery and synthesis of quantum dots. These nanoparticles have wide-ranging applications across fields like electronics, advanced surgery, and quantum computing.

The prize itself was embroiled in some controversy earlier when the names of winners were reportedly leaked to a Swedish newspaper. But Johan Åqvist, the chair of the deciding committee, said the decision hadn’t been final at the time. “There was a press release sent out for still unknown reasons. We deeply regret that this happened. The important thing is that it did not affect the recipients in any way,” he was quoted as saying by The Guardian.

What are quantum dots?

Quantum dots are particles that are a few nanometres wide. They exhibit unique optical properties due to their small physical size. Their structure and atomic composition are the same as bulk materials, but the properties of the latter don’t depend on their size.

In fact ,the properties of quantum dots can be changed by changing their size.

At the scale of nanometres, materials and particles are capable of new, size-dependent properties because quantum physical forces start to dominate. At the macroscopic scale, on the other hand, like in our day to day lives, gravity and the rules of classical physics dominate.

By the 1970s, physicists knew that the optical properties of glass could be changed by adding a small amount of another element, like gold, silver, cadmium, sulphur, or selenium. They also knew how or why some of these changes could occur, but quantum dots as such hadn’t been synthesised yet.

The Nobel-winning research

In the early 1980s, Dr. Ekimov succeeded in creating size-dependent quantum effects in coloured glass. From 1979, he studied the properties of glasses that were tinted with copper chloride, heated to a high temperature, and then cooled. He found that different ways of preparing this glass led to it absorbing light differently. This happened because the copper chloride formed tiny crystals, and that crystals of different sizes—depending on the preparation process—interacted with light differently.

In 1983, Dr. Brus and his colleagues went a step ahead and prepared similar crystals in a liquid solution, rather than in a glass. This allowed the researchers to better manipulate and study the crystals. These crystals also interacted with light differently depending on small variations in their size.

Finally, in 1993, Dr. Bawendi and his coworkers developed a technique to make these peculiar crystals—i.e. the quantum dots—of well-defined sizes and with high optical quality. This process began by injecting some substance (of which the dot would be made) into a hot solvent and then heating the solution. Nanocrystals automatically began to take shape, and larger particles formed when the solution was heated for longer. The solvent also ensured that the crystals had a smooth outer surface.

This method was quite easy, which meant many scientists could use it to make quantum dots that they required and study them.

Modern-day applications

Today, one of the simplest applications of quantum dots is to light computer monitors and television screens. Blue LEDs behind the screen excite these dots, causing them to emit light of different colours. Combining these colours gives rise to even more colours as well as brightness.

Nanoscale-sized quantum dots are also used to map biological tissues by biochemists.

Quantum dots are also used in photovoltaic cells to improve the absorption and efficiency in converting solar light into electricity.

Certain cancer treatments use quantum dots for targeted drug delivery and other therapeutic measures. This has wider applications in the field of nanomedicine too.

Quantum dots can be used as security markers on currency and documents as an anti-counterfeit measure. Broadly, they can be used as fluorescent markers to tag and track objects.