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.”
