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.

Left to right: Moungi Bawendi, Louis Brus and Alexei Ekimov.
| Photo Credit: Niklas Elmehed/Nobel Prize Outreach

The 2023 Nobel Prize for chemistry has been awarded to Alexei Ekimov, Louis Brus, and Moungi Bawendi for their work on quantum dots – very small crystals with peculiar properties that have found application in a variety of fields, from new-age LED screens to quantum computers.

Earlier in the day, reports emerged that the Nobel Committee had inadvertently revealed the names of the winners in an email, accessed by the Swedish press, in an unusual break from a tradition in which the identity of the laureates remains a closely guarded secret until the announcement.

Quantum dots are crystals just a few nanometres wide, holding only a few thousand atoms. To compare, a single grain of sand can hold around a sextillion atoms. The electrons in the dot’s atoms are very close to each other, with little wiggle room. At this nanoscale, the effects of quantum mechanics are more apparent.

When some light is shined on a quantum dot, it will absorb and re-emit it at a different frequency, or colour – just like some atoms. Uniquely, the colour depends on the size of the dot: the smaller the dot, the bluer the colour of the re-emitted light. This relationship between size and colour is the result of electrons in the atoms jumping from a lower to a higher energy level, before jumping back. The gap between these levels depends on the size of the dot.

In the early 1980s, Dr. Ekimov and Dr. Brus (separately) synthesised the first quantum dots in glass and a liquid, respectively, proving the existence of such crystals and confirming their ability to fluoresce light of different colours based on their size. But they both had a problem: they couldn’t consistently synthesise high-quality dots.

In 1993, Dr. Bawendi and his team had the answer. They injected small dollops of a compound into a specific solvent until it was saturated, and heated the solution. The compound soon began to coalesce into nanocrystals in the liquid, with the solvent itself giving them a smooth shape. Larger crystals formed when the solution was heated for longer.

“Quantum dots are … bringing the greatest benefit to humankind, and we have just begun to explore their potential,” the Royal Swedish Academy of Sciences said in a statement. “Researchers believe that in the future, quantum dots can contribute to flexible electronics, miniscule sensors, slimmer solar cells, and perhaps encrypted quantum communication.”

The 2023 Nobel Prize in Chemistry has been awarded to Moungi G. Bawendi, Louis E. Brus and Alexei I. Ekimov for the discovery and synthesis of quantum dots, the Royal Swedish Academy of Sciences said in Stockholm.

Quantum dots have unique properties and now spread their light from television screens and LED lamps. They catalyse chemical reactions and their clear light can illuminate tumour tissue for a surgeon, the Academy said in a press release.

Researchers have primarily utilised quantum dots to create coloured light. They believe that in the future quantum dots can contribute to flexible electronics, miniscule sensors, slimmer solar cells and perhaps encrypted quantum communication.

Today quantum dots are an important part of nanotechnology’s toolbox. The 2023 NobelPrize laureates in chemistry have all been pioneers in the exploration of the nanoworld, said the Academy.

In the early 1980s, this year’s chemistry laureates Louis Brus and Alexei Ekimov succeeded in creating — independently of each other — quantum dots, which are nanoparticles so tiny that quantum effects determine their characteristics.

In 1993, chemistry laureate Moungi Bawendi revolutionised the methods for manufacturing quantum dots, making their quality extremely high — a vital prerequisite for their use in today’s nanotechnology.

“Quantum dots are thus bringing the greatest benefit to humankind. Researchers believe that in the future they could contribute to flexible electronics, tiny sensors, thinner solar cells and encrypted quantum communication – so we have just started exploring the potential of these tiny particles,” the release added.

Last year the prestigious Prize was cinched by Carolyn R. Bertozzi, Morten Meldal and K. Barry Sharpless for the development of click chemistry and bioorthogonal chemistry. Their work in click chemistry has been used to develop pharmaceuticals, mapping DNA while bioorthogonal chemistry refined the pharmaceuticals used to treat cancer.

On October 3, the Royal Swedish Academy of Sciences announced the winners of this year’s Nobel Prize in Physics which was shared by Pierre Agostini, Ferenc Krausz and Anne L’Huillier for “experimental methods that generate attosecond pulses of light for the study of electro dynamics in matter.”

The Nobel Prize for Medicine or Physiology was granted to Katalin Karikó and Drew Weissman for their “discoveries concerning nucleoside base modification that enabled the development of effective mRNA vaccines against COVID-19.”

The recipients of the Nobel Prize in Literature will be announced on October 5 followed by the Prize for Peace on October 6 while the Prize for Economic Sciences will be released on October 9.

The prizes carry a cash award of 10 million Swedish kronor (nearly $900,000) and will be awarded on December 10. The money comes from a bequest left by the prize’s creator, Swedish inventor Alfred Nobel, who died in 1895.