To put it simply, quantum dot is a semiconductor, the electrical characteristics of which depend on its size and shape. Adjusting the size of the quantum dot, we can change the energy of the emitted photon, and hence can change the color emitted by the quantum dot of light. The main advantage of quantum dots lies in the possibility of changing the size, fine-tune the wavelength of the emitted light.
Quantum dots — fragments of a conductor or semiconductor (such as InGaAs, CdSe, or GaInP/InP), charge carriers (electrons or holes) which are limited in space in all three dimensions. The size of the quantum dots must be so small that quantum effects were significant. This is achieved if the kinetic energy of the electron is considerably greater than all other energy scales, primarily more than the temperature expressed in energy units.
To put it simply, quantum dot is a semiconductor, the electrical characteristics of which depend on its size and shape. The smaller the crystal size, the longer the distance between the energy levels. The transition of an electron energy level lower emitted photon. Adjusting the size of quantum dots, we can change the energy of the emitted photon, and hence can change the color emitted by the quantum dot of light. The main advantage of quantum dots lies in the possibility of changing the size, fine-tune the wavelength of the emitted light.
Quantum dots of different sizes can be assembled into a gradient multi-layer nanofilms.
There are two types of quantum dots (based on the method of creation):
– epitaxial quantum dots;
– colloidal quantum dots.
Colloidal quantum dots are an excellent replacement of traditional organic and inorganic phosphors. They surpass them by brightness of fluorescence, the photostability, but also possess some unique properties.
In particular, fluorescence of quantum dots depends on their size – so small (~2 nm) CdSe nanocrystals luminesce in the blue region of the spectrum, and the size of about 7 nm in the red. This property allows to obtain quantum dots with almost any wavelength of the fluorescence from the UV to near-infrared by changing the particle size and the nature of the semiconductor forming the nanocrystal.
It is equally important that the quantum dots have very wide (any wave length less than the exciton peak absorption) absorption spectrum, and thus quantum dots of different sizes can be excited with a single source of light. This effect is used to multiplex analysis of biological macromolecules (e.g., immunoassay). The peaks of photoluminescence of quantum dots is quite narrow (width at half maximum of less than 30 nm) and symmetric, it is also very important while identifying multiple fluorescent signals.
Quantum dots can be delivered in a form suitable for further covalent joining of biological molecules as well as polymeric microspheres.
– for various biochemical and biomedical research, including multicolor imaging of biological objects (viruses, cell organelles, cells, tissue) in vitro and in vivo, and also as a passive fluorescent markers and active indicators to estimate the concentration of a certain substance in a particular sample,
– for multi-channel optical coding, for example, in flow cytometry and high-performance analysis of proteins and nucleic acids,
– to study the spatial and temporal distribution of biomolecules by confocal microscopy,
– in an immunoassay,
– when in situ diagnosis of cancer markers,
– in blotting
– as a source of white color
– in LEDs,
– in semiconductor technology
– in TVs, displays, quantum dots and multi-touch screens with quantum dots in the backlight,
– in solar batteries as a material that converts solar energy into direct electric current (allows to achieve an effective absorption of several different parts of the spectrum of solar radiation).