Spontaneous emission

A - atom in the excited state (electron at E2 energy level) B - photon emission (hν) C - atom in low energy state (electron at E1 & lt; E2)

Spontaneous emission occurs when electrons on levels excited spontaneously return to lower energy levels, emitting photons.

The phenomenon occurs universally and is responsible for almost every luminescence of bodies, eg warm gases, excited atoms, liquid and solid bodies, as well as electronic devices such as light emitting diodes (LED).

The number of body spontaneous emissions in which the excited state is N atoms is given by the formula: & # x2202; N & # x2202; t = & # x2212; A 21 N {\displaystyle {\frac {\partial N}{\partial t}}=-A_{21}N} ,

where A21 is a constant emission factor for a given atomic transition (constant introduced by Einstein).

In the absence of new excitations, this leads to the equation determining the number of atoms remaining in the excited state: N ( t ) = N ( 0 ) e & # x2212; t τ 21 {\displaystyle N(t)=N(0)e^{-{\frac {t}{\tau _{21}}}}} ,

where: N (0) the initial number of excited atoms, τ21 is the lifetime and is associated with the coefficient A, τ21 = (A21).

Other photon emission methods:

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