Let us suppose that the size of a substance becomes smaller and smaller. When it attains the size of a ‘Nanoparticle’ (1-100 nm), its properties change drastically. Thus, the quantum effects come into existence.
The Nobel Prize winners of 2023 explored the world of Nanoparticles. They synthesized nanoparticles known as quantum dots.
Moungi G. Bawendi, Louis E. Brus and Aleksey Yekimov received the Nobel Prize in Chemistry 2023.
Quantum dots are tiny nanoparticles. It was in 1983 that Moungi Bawendi gave us the method for producing quantum dots in the laboratory.
Today, we use the properties of the quantum dots in our lives.
A quantum dot is a small crystal. Hence, it may have hundreds or thousands of atoms.
Even before the discovery of Nanoparticles, some scientists predicted from the famous Schrodinger’s equation that when a particle becomes extremely small, the electrons are confined to move in a limited space, say a three-dimensional box. Thus, the electrons behave as waves and thus result in drastic changes in properties.
The three-dimensional box leads to the quantization of energy. A particle absorbs radiation and emits a characteristic wavelength. The Schrodinger’s equation helps to understand the phenomenon.
Based on such assumptions, scientists predicted size-dependent quantum effects.
However, the Nanoparticles or the quantum dots were yet to be discovered.
Story of Colored Glass.
Some scientists accidentally found some unique phenomenon in the composition of coloured glass.
In ancient times, there were different glasses with different colours.
While manufacturing glass, they added a trace amount of silver, gold or cadmium and heated it to a higher temperature.
Thus, they produced shades of different colours.
Hence, while studying coloured glasses, they found that a single substance can change the colour of the whole glass.
For example, CdSe and CdS.- Their presence in glass results in either yellow or red colour glass.
Thus, they found that the colour arises from the particles inside the glass and depends on their size.
Similarly, they manufactured glass with nano-sized crystals of copper chloride- embedded in the glass.
The colour of the glass was because of the presence of Nanoparticles of CuCl2.
Hence, they discovered a size-dependent quantum effect.
Hence, quantum dots absorb light and emit it at other wavelengths, showing different colours.
These were the first quantum dots ever produced.
Synthesis of Quantum Dots by Moungi Bawendi.
Moungi Bawendi injected a substance that can form Cadmium Selenide into the hot solvent.
The crystals started growing when he raised the temperature.
Applications of Quantum Dots
Quantum dots create coloured light.
We can alter the colour they glow with if we change their size.
Quantum dots make it possible to produce three primary colours of light needed on a television screen.
In addition, they are using them for tracking tumours in the body and LED lamps & in catalysis.
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