The following is an Bohr model (1913) of an atom showing a photon absorbing into an electron, causing it to go up ↑ in orbital position, and photon emitting from an electron causing it to go down ↓ in orbital position:
The term “photon” was first employed by: Leonard Troland (1917), intermixed with “light element” (Compton, 1923), and again photon (Millikan, 1924), citing Compton. The solidified coining, however, was done by Lewis, who defined it as a light particle:
- “I therefore take the liberty of proposing for this hypothetical new atom, which is not light but plays an essential part in every process of radiation, the name photon.”
- — Gilbert Lewis (1926), “The Conservation of Photons” (pg. #)
The following are quotes:
- “Light — an electromagnetic field of certain wavelength range — is a stream of photons; those of light are on the mass shell, those of electric and magnetic fields are not.”
- — Martinus Veltman (2003), Facts and Mysteries in Elementary Particle Physics 
- Veltman, Martinus. (2003). Facts and Mysteries in Elementary Particle Physics (pg. 17). World Scientific.
- Photon – Hmolpedia 2020.