In order to get a general idea of the properties of material objects and the laws in accordance with which the macrocosm familiar to everyone “lives”, it is not at all necessary to graduate from a higher educational institution, because every day everyone faces their manifestations. Although the principle of similarity has been increasingly mentioned lately, supporters of which claim that the micro and the macrocosm are very similar, nevertheless, there is a difference. This is especially noticeable with very small sizes of bodies and objects. Quantum dots, sometimes called nanodots, just represent one of these cases.
Less less
Let's recall the classic structure of an atom, such as hydrogen. It includes a nucleus, which, due to the presence of a positively charged proton in it, has a positive electric charge, that is +1 (since hydrogen is the first element in the periodic table). Accordingly, at a certain distance from the nucleus is an electron (-1), forming an electron shell. Obviously, if you increase the value of the nuclear charge, this will entail the addition of new electrons (recall: in general, an atom is electrically neutral).
The distance between each electron and nucleus is determined by the energy levels of negatively charged particles. Each orbit is constant, the total configuration of particles determines the material. Electrons can jump from one orbit to another, absorbing or releasing energy through photons of one frequency or another. At the most distant orbits are the electrons with the maximum energy level. Interestingly, the photon itself exhibits a dual nature, being defined simultaneously as a massless particle and electromagnetic radiation.
Terms
The very word "photon" of Greek origin, it means "particle of light." Therefore, it can be argued that when an electron changes its orbit, it absorbs (emits) a quantum of light. In this case, it is appropriate to explain the meaning of another word - "quantum". In fact, there is nothing complicated. The word comes from the Latin "quantum", which literally translates as the smallest value of any physical quantity (here - radiation). Let us illustrate with an example what a quantum is: if milligrams were the smallest indivisible value when measuring weight, then it could be called that. This is how a seemingly complex term is simply explained.
Quantum dots: clarification
Often in textbooks you can find the following definition for a nanodot - it is an extremely small particle of any material, the dimensions of which are comparable to the magnitude of the emitted wavelength of the electron (the full spectrum covers the range from 1 to 10 nanometers). Inside it, the potential energy of a single negative charge carrier is less than outside; therefore, the electron is limited in displacements.
However, the term "quantum dots" can be explained differently. The electron that has absorbed the photon “rises” to a higher energy level, and in its place forms a “shortage” - the so-called hole. Accordingly, if an electron has a -1 charge, then a hole is +1. In an effort to return to its former stable state, the electron emits a photon. The connection of charge carriers “-” and “+” in this case is called an exciton and in physics is understood as a particle. Its size depends on the level of absorbed energy (higher orbit). Quantum dots are precisely these particles. The frequency of the energy emitted by the electron directly depends on the particle size of the given material and the exciton. It should be noted that the basis of the color perception of light by the human eye is the different energy of the photons. Each color has a specific frequency of electromagnetic radiation.