The mechanism of luminescence consists of the formation of excited states of atoms, molecules or crystals under the influence of energy from an external and internal source, followed by the emission of light quanta (photons).

By the duration of light emission determined by the lifetime of the excited states, a distinction is made between fluorescence (rapidly decaying luminescence) and phosphorescence (prolonged luminescence).

According to the mechanism of excitation a distinction is made between the following classes of luminescence:

- photoluminescence;

- electroluminescence;

- chemiluminescence;

- cathode luminescence;

- X-ray luminescence;

- radioluminescence;

- sonoluminescence.

The most widely used in photonics are sources and converters of light radiation that use electroluminescence (light-emitting diodes, semiconductor injection lasers and amplifiers) and photoluminescence (luminescent coatings, lasers and amplifiers based on rare earth elements, etc.).

Luminescence spectra analysis is one of the most important spectroscopic methods for studying composition and structure of substances. Luminescence techniques make it possible to determine the size, concentration and spatial distribution of nanoparticles, lifetimes of excited states (for example, of nonequilibrium charge carriers in bulk and nanoscale semiconductor structures), etc.

An exceptionally important contribution to the determination of the basic laws of luminescence and development of its applications was made by the Soviet school of physicists established by S. I. Vavilov.