Calcite & Willemite in UV Light, Buckwheat Dump, Franklin, NJ
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. Most emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. However, when the absorbed electromagnetic radiation is intense, it is possible for one electron to absorb two photons; this two-photon absorption can lead to emission of radiation having a shorter wavelength than the absorbed radiation.
Fluorescence occurs when an orbital electron of a molecule, atom or nanostructure relaxes to its ground state by emitting a photon of light after being excited to a higher quantum state.