Fluorescence is the emission of energy during exposure of the diamond to ultraviolet light. Fluorescence stops when the radiation stops.
Not all diamonds have fluorescence (only 50% or so).
If the stone doesn’t have fluorescence it does not mean that this is not a diamond, but if the stone does have fluorescence it is certain that it`s a diamond
Fluorescence will generally be in shades of blue, purple, but there are other Fluorescence sectors like green, yellow and more.
There are four levels of common Fluorescence: