05 October 2023

2023 Nobel Prize in Chemistry awarded for the discovery and synthesis of ‘quantum dots’

The Royal Swedish Academy of Sciences has awarded the 2023 Nobel Prize in the field of Chemistry to Moungi G. Bawendi, at Massachusetts Institute of Technology (MIT), Louis E. Brus, at Columbia University, and Alexei I. Ekimov at Nanocrystals Technology Inc., for their roles in the discovery and synthesis of quantum dots.

Quantum dots are semiconducting nanoparticles having diameters as small as a few nanometres. Quantum dots are often made up of only a few thousand atoms. To put this in perspective, a quantum dot has the same relationship to the size of a football, as the football has to the size of the Earth. Due to their size, quantum dots have certain properties of both bulk semiconductor materials and individual atoms or molecules, making them useful across various applications.   

When quantum dots are illuminated, electrons are excited from their valence band into their conductance band (photoexcitation). When the excited electron drops back into the valence band, energy is released in the form of light. This is a phenomenon known as photoluminescence. The optoelectronic properties of quantum dots can be adjusted by changing their size and possibly even their shape. The wavelength of the photoluminescence can therefore be fine-tuned in order to emit a specific desired wavelength of visible light.

Quantum dots were first intentionally prepared by Alexei Ekimov during experiments on the effects of dopants on the colour of glass. Ekimov discovered that glass containing copper chloride crystals would have a different colour depending on the crystal’s size. However, Ekimov lived in the Soviet Union where his work was not accessible to scientists on the other side of the iron curtain. Unaware of Ekimov’s work, Louis Brus was the first to prepare quantum dots floating freely in a solution. Brus was working with cadmium sulphide nanoparticles when he discovered that their optical properties would change over time as the particles grew in size.

Almost a decade later, a major breakthrough was achieved by Moungi Bawendi who succeeded in growing nanocrystals of reliable and specific sizes. Bawendi’s preparation methods were easy to use and made quantum dot science much more accessible to scientists around the world.

Today, quantum dots find application in various optoelectronic devices. The light emitting properties of quantum dots are useful in the emerging technology of quantum dot display screens. Quantum dot displays allow for the wavelength emitted by the quantum dots to be precisely controlled. This results in vibrant and true-to-life colour reproduction, surpassing that of conventional LCD and OLED displays. Quantum dot displays offer a more visually impressive display as well as being more eco-friendly and energy-efficient than conventional display devices.

Quantum dots are also capable of the very similar process of turning light into electricity, which forms the basis of solar cells. Unlike traditional solar cell materials, quantum dots can have a wide range of band gaps depending on their size. This means that by taking advantage of mixtures of quantum dot sizes, these mixtures can be made to absorb a wide range of wavelengths from the sun’s rays. This can lead to much more efficient electricity production than is possible using conventional solar panels, which only absorb a narrow range of wavelengths allowing much of the energy to go to waste.

It is clear that Ekimov, Brus, and Bawendi have made a considerable scientific contribution, which will enable whole new fields of research and technology to be realised. Development of new quantum dot based optoelectronic devices is ongoing and is certainly an area in which we expect to see more exciting developments in the future.