Little Glowy Things

See these?

Shiny.

These are called quantum dots. They are incredibly tiny semiconductors, the applications of which are nearly endless. And you’ve probably never heard of them. 

Electricity is basically defined as the movement of electrons from atom to atom. In some substances, called conductors, these electrons move fast and freely; in others, insulators, it’s a little tougher to get them going. Semiconductors are sort of in the middle. Most of the electrons in the atom move around, but some stay where they are. The spatial difference between the moving conduction electrons on the outside of the atom and the fixed valence electrons on the inside is called the band gap. 

Now, this band gap is pretty prominent in most semiconductors; it’s what makes them ‘semi’, since there are a certain number of electrons that can’t move and therefore can’t contribute to the flow of electricity. In fact, for a valence electron to cross this band gap, it needs quite a bit of energy, normally in the form of heat or light. Then, when that energy stops coming, the electron drops back down into the valence layer, giving off the energy it had absorbed. 

Enter quantum dots. Quantum dots are basically semiconductive crystals that have been synthesized to be as small as possible, normally from 2-30 nanometers wide. Why so small? Quantum mechanics dictates that the smaller the dot, the larger the band gap; the larger the band gap, the more energy is given off when an excited electron goes back down into the valence layer. This energy can come in the form of visual light (like the solutions of quantum dots shown above) or plain chemical energy. Quantum dots can be synthesized so accurately that they can be tuned to absorb and release specific energy amounts. This degree of customization makes quantum dots an invaluable piece of technology. 

For starters, quantum dots are already being investigated for application in quantum computing. Their unique reactions to electrical flow could be harnessed to complete more computations in a second than a silicon chip could ever do. Their luminescent properties are being utilized in medical research as a better, more efficient replacement for traditional dyes. Quantum dots shine brighter, last longer, and are often less toxic than dyes previously used. In addition, specific organic molecules can be attached to the quantum dot to better track a critical area in the body, be it a healthy cell, a virus, or a mutation. 

Cells illuminated by quantum dots.
Or else they're alien eggs. I can't really tell. But it's all science anyway.

Solar cells also utilize quantum dots. An efficient solar panel today is only capable of converting, at most, 33% of the sun’s energy into energy we can use; this means that a solar panel a square meter large, absorbing the 1,368 watts of sunlight shining down on it (the solar constant), can only use around 450 watts for electricity. But by covering a solar panel with enough quantum dots, the amount of sunlight absorbed can go up sevenfold, bringing the efficiency ratio up to 42%. Given that the maximum theoretical efficiency of a solar cell can only be 86%... that’s a pretty good jump. 

As of now, quantum dots are still time-consuming to produce; after all, growing hundreds of custom-made crystals nanometers in size can’t be that easy. However, as technology gets better and the production process becomes faster, these problems won’t be problems anymore! Think of the possibilities! 

Quantum Dots: a fantastic example of what Physics can do. 

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