Quantum Dots Properties

## Quantum Dots, the Color Master

Quantum Dots are tiny semiconductor particles. They are composed of different types of atoms, such as cadmium, selenium, copper, and/or zinc. In all cases, the Quantum Dot is a capsule in which there is a confinement of one or more electrons, or one or more holes (a deficiency of electrons).

Perhaps the most studied and valued property of Quantum Dots is their fluorescence. The emission of photons of a specific wavelength when excited by an external electric or light source makes Quantum Dots a very unique nanomaterial. Additionally, the wavelength of the emitted light depends on the precise size of the Quantum Dots, for a given specific shape and composition.

## From Quantum Dots Size to Color

Imagine that we have a special recipe to synthesize Quantum Dots by mixing only two types of atoms, which always results in spherical particles. At the start of this synthesis, atoms begin to aggregate to form the first seeds of Quantum Dots. When left to cook for longer, more atoms are added to these Quantum Dot seeds, allowing them to grow larger. The small Quantum Dots at the start of this synthesis and the larger Quantum Dots obtained at the end are of the same composition, same form, but of different sizes. This difference in size will result in a different emitted wavelength of light, thus a different color. Hence, if our Quantum Dots emit within the visible spectrum of light, smaller Quantum Dots will provide a shorter wavelength, or color closer to blue, while larger Quantum Dots will provide a longer wavelength, or color closer to red.

However, this process is not limited to only the visible spectrum. It is possible to create much larger Quantum Dots that emit in the infrared, or much smaller Quantum Dots that emit in the ultraviolet range.

## Mastering Quantum Dot Synthesis

The first important steps of the synthesis method are:

having a very low size dispersion of Quantum Dots during their synthesis. If we want to utilize Quantum Dots for their optical properties, which is always the case in real life applications, it is necessary to have uniform particle sizes to obtain the same color. If the Quantum Dots of different colors are mixed in the final solution, purification to obtain a pure color will be long and difficult.

being able to precisely adjust the size of the Quantum Dots synthesized, so that each batch has exactly the same properties, otherwise they will be difficult to use industrially.

## More Powerful Quantum Dots

The control on the shape of Quantum Dots obtained is thus very interesting. The first methods of synthesis allowed researchers to obtain spherical nanocrystals, with a confinement of charge in three dimensions. Today, it is possible to make cylindrical Quantum Dots (confinement in two dimensions), or flat (confinement in one dimension) like the Quantum Plates developed at Nexdot.

The shape influences the intrinsic properties of Quantum Dots. For example, Quantum Plates are brighter than spherical Quantum Dots with equal excitation, and emit light in one direction only.

Cylindrical Quantum Dots and Quantum Plates also have advantages in certain applications. It is possible to synthesize a “connector” at each end of a cylindrical Quantum Dot. In the case of Quantum Plates, they can be easily assembled and aligned with respect to each other.