Discovery and Synthesis of Quantum Dots Wins 2023 Nobel Prize in Chemistry
Moungi G. Bawendi, Louis E. Brus and Alexei Ekimov share the 2023 Nobel Prize in Chemistry.
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The 2023 Nobel Prize in Chemistry has been awarded to Moungi G. Bawendi, the Lester Wolfe Professor of Chemistry at the Massachusetts Institute of Technology, Louis E. Brus, the S. L. Mitchell Professor of Chemistry at Columbia University and Alexei Ekimov, chief scientist at Nanocrystals Technology Inc.
Bawendi, Brus and Ekimov share the prize for their discovery and synthesis of quantum dots – special nanoparticles that are so tiny that their size determines their properties. A crucial part of modern nanotechnology, quantum dots have enabled significant advances in light-emitting diode (LED) displays and medical imaging, among other applications.
Harnessing quantum phenomena
An element’s properties are directly governed by how many electrons it has – this is a fundamental underpinning of chemistry. But when we shrink things down to the quantum realm, chemistry gets weird.
When particles are just a few nanometers in diameter, the space available to their electrons shrinks. This effectively compresses the wavefunction of the electrons, resulting in significant changes to the particle’s properties. This is most visible when looking at a particle’s optical properties; as nanoparticles shrink and the space for electron waves reduces, the color of the light emitted by the nanoparticles will go from red to yellow to green to blue.
Quantum dots are semiconductor particles measuring less than 10 nanometers in size and are made up of just a few thousand atoms in total. Due to their size, the same strange quantum phenomena play a significant role in controlling how the dots absorb and release visible light. But it’s not just the color of a quantum dot that changes with its size –a dot’s melting point, thermodynamic properties and more can be also affected by quantum phenomena.
For this reason, quantum dots are sometimes thought of as being a new class of material, one where you can change the material properties of what you are working with not by swapping it out for an entirely different material, but just by changing its size.
Making the impossible quantum dots
The theoretical basis for tiny nanoparticles with unique size-dependent color-change properties had been laid as early as the 1930s, but few at the time believed that such particles would ever be of practical use. To do so would require the synthesis of perfectly crystalline structures and precise enough control to sculpt atom layer-by-atom layer in nano-dimensions.
In the early 1980s, Alexei Ekimov succeeded in creating size-dependent quantum effects in colored glass. The unique color properties of the glass stemmed from nanoparticles of copper chloride that were held in the glass, with Ekimov able to prove that the copper nanoparticle size had directly affected the color of the glass via quantum effects.
A few years later, Louis Brus would independently make a very similar discovery, this time for nanoparticles floating freely in a fluid.
Moungi Bawendi would revolutionize the production of quantum dots in 1993, with his invention of an ingenious nanoparticle synthesis method that could produce almost-perfect nanoparticles. By specifically controlling the moment in time where crystal nucleation begins, Bawendi’s method made it possible to synthesize quantum dots of high enough quality that they could be utilized for applications outside of the chemistry lab.
Speaking via a telephone link in the official Nobel press conference, Bawendi told of his shock at being awoken by a phone call telling him that he was to be awarded the 2023 Nobel Prize in Chemistry
“I was very surprised, sleepy, shocked and very honored,” he told the assembled audience.
In a touching first reactions interview, Bawendi spoke of his life as a researcher and told of how he has tried to emulate the style and mentorship exhibited by his co-laurate Brus, who was also Bawendi’s postdoc supervisor, with his own students.
Where are quantum dots used?
The optical properties of quantum dots have attracted significant interest in recent decades. Today, quantum dots can be found in a range of everyday products. They might be embedded in pigments, dyes or in high-tech reflective paints to boost their performance. Thin films made up of quantum dots are also sometimes placed on top of fluorescent lamps, to convert their harsh blue light into colors that are easier on the human eye.
An alternative to the organic LED (OLED) display and an improvement on traditional LED screens, the quantum dot LED (QLED) display also harnesses quantum dots as photo-emissive particles to display wider color gamuts with exceptional contrast and luminescence.
Outside of the home, quantum dots can be used in place of organic dyes for medical imaging and biological research.
But that is not where the application of quantum dot technology ends – the field is still very active. Researchers looking into quantum computing are exploring the possibility that so-called “optical computers” could use quantum dots in the same way that current electronic computers use transistors. Research is also ongoing with their application in areas such flexible electronics, improved sensors, solar cells and catalysis for solar fuels.