Spontaneous emission is the transition of atoms under the action of a vacuum field. Even if there is no artificially applied radiation field in the space, there will be a zero-point field spontaneously, that is, a vacuum field with radiation field mode n=0. Under the action of this radiation field, the atom will spontaneously transition from the upper energy level to the lower energy level, and at the same time emit a photon with energy hν into the radiation field. Spontaneous radiation is a spontaneous process that is not affected by the external radiation field. Each atom is independent of each other during the spontaneous transition. The spontaneous radiation generated by different atoms has a certain degree of arbitrariness in frequency, phase, polarization direction and propagation direction.
Therefore, spontaneous emission light is irrelevant fluorescence, and the energy of the spontaneous emission light field is distributed in a wide frequency range. The light-emitting process of ordinary light sources is the spontaneous emission process of a large number of atoms at a high energy level. Common light sources such as neon lights, fluorescent lights, LEDs and other common light sources are essentially spontaneous emission.
Spontaneous emission, also known as spontaneous emission, quantum transition, is a luminous process of atoms. Atoms are excited to transition from a low energy level to a high energy level. Atoms in a high energy level (excited state) are unstable. Without any external influence, they will spontaneously and independently return from a high energy level to a low energy level, and release one at the same time. The photon with energy hν=E2-E1. This process of spontaneously returning from an excited state to a lower energy state to emit photons is called the spontaneous emission process. The radiation process that excites atoms to spontaneously transition to lower energy levels. The electrons in the high energy level E2 in the atom generally have to transition to the lower energy level E1, and at the same time emit energy of E2 -E1 of light radiation. If this process occurs spontaneously without being affected by external factors, it is called spontaneous radiation. It is the light-emitting mechanism of ordinary light sources.
This process has nothing to do with external effects. The radiation of each atom is carried out spontaneously and independently. The phases are all different. Moreover, because there is more than one excited state of the atom, different atoms may be in different excited states, so the frequency of spontaneous emission is not single. The light emitted by ordinary light sources (such as incandescent lamps, fluorescent lamps, arc lamps, etc.) is mainly produced by spontaneous radiation. It is incoherent light.
The difference between spontaneous emission and stimulated emission
Spontaneous emission: In an excited atom, an electron can only stay at the excited state energy level for a short period of time, and then spontaneously transitions to a lower energy level and radiates a photon at the same time. This kind of radiation is called spontaneous radiation.
Simulated emission: When the atom is in the excited state E2, if a photon of energy (here E2>E1) comes, under the influence of the incident photon, the atom will Emitting a same photon and jumping to the lower energy level E1, this kind of radiation is called stimulated radiation.
Difference: Unlike spontaneous radiation, radiation must occur under the action of external light and emit a photon identical to the external photon. Stimulated emission light is coherent light. The stimulated emission light plus the original external light can amplify the intensity of the light in the propagation direction. Spontaneous radiation is a spontaneous process that is not affected by the external radiation field. Each atom is independent of each other during the spontaneous transition. The spontaneous radiation generated by different atoms has a certain degree of arbitrariness in frequency, phase, polarization direction and propagation direction.