spontaneous emission

That mode of emission which occurs even in the absence of a perturbing external electromagnetic field. The transition between states, n and m, is governed by the Einsteincoefficient of spontaneous emission, A n m.
See also: stimulated emission
Source:
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2277