Krypton discharge ampoule (Kr), 99.999%, 18x100 mm.

Any substance consists of molecules, and its physical properties depend on how the molecules are ordered and how they interact with each other. In ordinary life, we observe three states of aggregation of matter - solid, liquid and gaseous. There is, however, a fourth state, which physicists are inclined to attribute to the number of aggregates. This is a plasma state. Plasma is characterized by partial or complete stripping of electrons from their atomic orbits, while the free electrons themselves remain inside the substance. Thus, the plasma, being ionized, as a whole remains electrically neutral, since the number of positive and negative charges in it remains equal. Glowing ampoules are plasma .. Why do gases glow after all? The fact is that the gases injected into the ampoules consist of billions and billions of atoms. Each atom has electrons in its orbit around the nucleus. When electrons enter the electromagnetic field of the Tesla coil, they begin to jump from atom to atom, as they should be when a current passes. Gas atoms are excited when they collide with electrons. Electrons in an atom of gases are not prone to vagrancy, therefore, after excitation, the atom calms down and the electrons return to their place. As a result, the atom emits a photon of light. The energy of photons in different atoms is different and, accordingly, lies in different parts of the spectrum of visible light, so gases glow in different colors.