Spontaneous emission - definition

Spontaneous emission is a quantum phenomenon involving the spontaneous transition of an excited atom, molecule or other quantum system to a lower energy state accompanied by the emission of a photon. This process occurs without the involvement of an external electromagnetic field and is one of the primary mechanisms for the interaction of matter with radiation.

In atomic physics, spontaneous emission describes the deexcitation of an electron from a higher energy state to a lower one, resulting in the release of a portion of energy in the form of a photon with a frequency corresponding to the difference in energy levels. Because this process is random and uncontrolled, the emitted radiation is random in phase, direction and polarisation. This distinguishes it from forced emission, in which a photon initiates the transition and radiation with the same parameters as the excitation photon is produced, which is crucial in the operation of lasers.

The probability of spontaneous emission occurring is described by the Einstein factor A, which depends on the properties of the energy levels and physical constants. The excited state lifetime, which is the inverse of this coefficient, determines how long an atom or molecule remains in an excited state before the emission of a photon.

Spontaneous emission plays a fundamental role in many fields of science and technology, including spectroscopy, solid state physics, astrophysics and light source technology. It is the primary mechanism for light emission in fluorescent lamps, light-emitting diodes (LEDs) and natural radiation sources such as stars. In optoelectronic systems, it affects the characteristics of light sources, optical noise and efficiency signal processing of light.

LEDs

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