When the photoelectric effect happens or blackbody radiation happens or when an electron jumps from a ground to an excited state, we say light is emitted by electron.

Now, light is made up of photons. So, can we say that electron emits photons?

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    – andselisk
    Mar 8 at 11:33

Electrons bound in atoms and molecules emit a photon at change of their quantum-allowed energy level, saving the total energy, momentum and angular momentum.

Free electrons emit photons, if they are accelerated and the time derivative of their acceleration is nonzero. This emission is very low for low speeds and/or accelerations.(*)

This effect is observed from the space, when lightnings are accompanied by short bursts of gamma-ray-like photons, created by Bremsstrahlung ( deceleration) radiation. Their origin is in decelerated electrons from ionized air, that were accelerated by during the lightning by the electrostatic potential gradient.

Electrons are not the only quantum objects able to emit photons. Most of subatomic particles and atomic nuclei can emit photon to reach their lower and allowed energy level. E.g. distinguishing between X-ray and gamma ray photons is not by their energy ( they largely overlap ), but by their origin. The origin of the former is energy change of inner electrons of heavy atoms, th eorigin of the latter is energy change of the nucleus.

(*) An electron circularly orbiting in a cyclotron or synchrotron emits synchrotron radiation, but a linearly accelerated electron with constant acceleration does not emit this radiation ( or minimally, as conditions cannot be exactly met ). This is the reason to built linear accelerators. They are on one hand limited by the 1-pass only, on the other hand there is no radiative energy loss, which is significant for high particle energies. Things get more complicated with relativistic effects at high speeds, but you can still get the picture.


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