How Fluorescence Occurs at the Atomic Level
An electron absorbs UV light energy from an ultraviolet
light source causing it to move to a higher energy orbit that is unstable.
The electron then returns to its normal orbit releasing the energy as both
heat and longer wavelength visible light. The fluorescing wavelength is
always longer (lower energy) since some of the energy is lost as heat in
the process. The small amount of heat generated is not noticeable in fluorescent
minerals. It has been estimated that around 15% of minerals fluoresce.
A few minerals fluoresce in their pure state, but most require the presence of other trace elements called activators to fluoresce. Common activators include the uranyl ion, the disulfide ion, manganese, chromium, and the rare-earth elements. In some cases, crystal structure defects can also serve to activate fluorescent minerals. Since activators are typically impurities in the mineral, a given mineral may fluoresce from some locations and not fluoresce in other locations where the activator is not present. In some cases, different activators can even produce different colors in the same mineral.