Quantum dots are nanoparticles of different colours depending on their size, primarily used to create coloured light
The winners of Nobel Prize in Chemistry, 2023. Photo: @NobelPrize / X (formerly Twitter)
_ The Nobel Prize in Chemistry 2023 was awarded to Moungi G Bawendi, Louis E Brus and Alexei I Ekimov for the discovery of quantum dots used in light-emitting diode or LED lights
Quantum dots are nanoparticles or small particles ranging between 1 and 100 nanometres in size. These are so tiny that their size determines their properties. The smallest quantum dots shine in blue and the big ones shine in yellow and red, and they only differ by size.
“Quantum dots have many fascinating and unusual properties. Importantly, they have different colours depending on their size,” Johan Åqvist, Chair of the Nobel Committee for Chemistry, said in a statement.
Researchers have primarily used quantum dots to create coloured light. These particles have found several applications — from helping spread light from television screens and LED lamps using their clear light to illuminate tumor tissue during surgery.
The first observation of these effects was made by Louis E Brus from Columbia University and Alexei I Ekimov from Nanocrystals Technology Inc. “For a long time, no one thought one could make such small particles. But this year’s laureates succeeded,” Åqvist said at the announcement on October 4, 2023.
In the early 1980s, Ekimov created size-dependent quantum effects in coloured glass, which gets its hue from nanoparticles of copper chloride. Ekimov demonstrated that the particle size affected the colour of the glass via quantum effects.
When particle size drops to a certain value, a critical limit is reached where the energy level separations normally experienced by a particle are effectively spread even further apart. This is called the quantum size effect. It follows quantum mechanics, a subfield in physics that describes the atomic world to a surprising degree of precision, according to the University of Waterloo.
Brus proved size-dependent quantum effects in particles floating freely in a fluid for the first time.
Moungi G Bawendi from the Massachusetts Institute of Technology helped make these quantum dots useful by making them in a solution with exquisite control of their size and surface.
He used a range of solvents, temperatures, techniques and a variety of substances to develop well-organised nanocrystals. Though the crystals were getting better, they were not good enough.
However, Bawendi continued his efforts to produce higher-quality nanoparticles. In 1993, he tasted success after his team injected the substances that would form nanocrystals into a heated and carefully chosen solvent.
The team succeeded in growing nanocrystals of a specific size by varying the temperature of the solution. These crystals also had a smooth and even surface.
Given their applications, the Nobel committee noted that quantum dots are bringing the greatest benefit to humankind and we have just begun to explore their potential. In the future, quantum dots could contribute to flexible electronics, miniscule sensors, slimmer solar cells and perhaps encrypted quantum communication.
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