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  • Samar Deshmukh

Quantum Dots- A new world of nano-colour

What is colour? To be more specific, what do we mean when we say an object is of a certain colour? When we see a colour of an object through our eyes, we are observing a certain wavelength of colour. But when white light strikes the object, why does only a certain wavelength come out? This  is because all the other wavelengths are absorbed by the object. On a molecular level, the electrons of the particles absorb the light and shift to a higher energy state farther away from the nucleus. In most cases, then, the nucleus takes that energy, and it goes into their vibration, which is why things get heated under the sun’s light.

However, for some other materials, instead of just absorbing light into heat, the electrons un-excite themselves by releasing specific wavelengths of light. Instead of just absorbing the other colours, it emits its own light to the colour which we want. This is called Luminescence.

If we make a nanocrystal barely a few nanometers big, the properties of light at the quantum scale as well as the properties of the crystal completely change, and they go from obeying our conventional physics to obeying quantum mechanics. These nanocrystals are so small that we call them quantum dots. They are luminescent, however they have some special properties which differentiate them from all other materials.

When studying biology at an extremely zoomed-in level, it is hard to discriminate between certain parts of a specimen, or even see what it is doing due to its transparency. This is why we ‘stain’ an organism, using fluorescent dyes to colour certain parts to increase the contrast and make it much easier to view in a microscope.

This is where quantum dots come in. They are much, much brighter than the ordinary dyes we use, and they are widely used in biology because of their immense brightness. In addition to that, after long exposure to light, ordinary dyes get photobleached, which means that they are chemically damaged from the light and don’t emit colour anymore. In contrast, quantum dots have a drastically larger lifespan and do not get photobleached easily.

Ordinarily, when we see a certain colour, we also see a range of colours that are near it, and not just one specific wavelength. But with quantum dots, they are very accurate in the wavelength that they emit, so they could also be used in our televisions to produce more accurate and distinct colours.

With light being one of the, if not the most enigmatic subject in the entire field of physics, and it having such a widespread and important use in technology ranging from lasers to microscopic biology, the discovery and the process of mass-production of quantum dots was a game-changing discovery. For this very reason, its discovery and synthesis were given the nobel prize in chemistry, in 2023. 

Because we have already figured out how to make quantum dots, a huge opportunity has been opened to apply this discovery to new technologies and inventions without having to produce quantum dots from scratch. With so much of the groundwork already done, it will be interesting to see where quantum dots are used in the future.

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