An optical ion trap holds a calcium ion which emits a ultraviolet-violet photon with a wavelength of 397 nm397\text{ nm}397 nm during a specific electronic transition.
Calculate, in eV\text{eV}eV, the change in the energy level of the calcium ion that is responsible for the emission of a photon of this wavelength.
Explain, with reference to the physical processes within the ion, the difference between how this emission line is produced compared to an absorption line of the same wavelength.
