The Nobel Prize in Chemistry was awarded to Moungi Bawendi, Louis Brus and Alexei Ekimov, on October 4, by the Royal Swedish Academy of Sciences, for their work on quantum dots – very small particles whose properties, such as colour, can be altered depending on their size.

Técnico professors and researchers shared their comments on the prize in several newspapers, such as an opinion piece in Público newspaper by Ermelinda Maçôas and an article in Expresso newspaper with statements by José Paulo Farinha.

What are quantum dots and why did they deserve this prize?

João Paulo Farinha (JPF): Quantum dots are semiconductor particles, often measuring a few nanometers (a meter is a billion nanometers). Their properties, such as colour, can be adjusted simply by changing their size.

The optical, electrical and magnetic properties of a material are normally determined by its chemical composition. However, at the nanometer scale – as is the case with quantum dots – the properties depend strongly on the size of the material. In the case of semiconductor particles, and for the same composition, the colour of the light they emit varies with their size. As the size of the quantum dots decreases, they absorb and emit light in increasingly energetic areas of the visible spectrum (the colour varies from red to blue).

This ability to tune optical properties by changing the size of the quantum dots, without the need to alter their composition, is at the root of their current technological applications and others that will appear in the near future.

Is there any research work on quantum dots at Técnico?

JPF: At IST, several researchers use quantum dots in their work, in the field of bio-imaging and others. I would highlight the work carried out in the area of graphene quantum dots in the Optical and Multifunctional Materials group, at Centro de Química Estrural (CQE).

What are the current technological applications of quantum dots? And what other applications do you foresee in the future?

JPF: Quantum dots are already widely used in LED lighting, in computer and television screens with QLED technology, and in biomedical research, as cell and tissue markers with high brightness and stability. It is expected that they could be used in quantum cryptography and solar cells, where, due to the quantization of energy levels, they can generate multiple charges by absorbing each photon, increasing the electrical energy produced and may even surpass the theoretical efficiency limit of current devices.

What are the contributions of the laureates to this area?

JPF: Ekimov discovered quantum dots, and was first to report the connection between their size and optical properties. Brust, working independently, later proved that their properties were due to quantum effects. Bawendi developed the process of producing quantum dots using molecules that control their size and stabilize the nanoparticles, which has made it possible to obtain quantum dots of precise dimensions and high quality, enabling to apply this technology on a large scale.

What other advances in the field of Chemistry would you like to have seen awarded?

JPF: There are so many possibilities! Thinking of nanotechnology, we should mention metallic nanoclusters, particles with few metallic atoms (dimensions below 2 nanometers). For example, gold nanoclusters are photostable and biocompatible, emitting light of a colour defined by their dimensions (like quantum dots), and can replace natural and synthetic dyes in bio-imaging and other applications. They also have magnetic properties and very promising catalytic activity for application in biocatalysis, photocatalysis and electrocatalysis.

Another hypothesis is controlled radical polymerization, a technology that has revolutionized the production of polymers with extremely well-defined size, composition and architecture, and which are often used in the self-assembly production of various nanostructured materials.

Finally, I would add MOFs (metal-organic frameworks), nanostructured hybrid materials with high porosity and versatile compositions, with very promising applications in such important areas as catalysis, carbon dioxide capture, fuel storage (hydrogen and methane, for example), environmental remediation and controlled drug delivery, among many others.