Fluorescence
Fluorescence , noun
[From Fluor.]
The color of the radiated light typically differs from the apparent color of the material, as when green crystals of fluor spar afford blue reflections. It is due not to the difference in the color of a distinct surface layer, but to the power which the substance has of modifying the light incident upon it, by first absorbing the light to achieve an excited state, and then radiating light to resume the ground energy level. The light emitted by fluorescent substances is in general of longer wavelength than the incident light. The radiation can also be induced by ionizing radiation which is not electromagnetic, such as alpha or beta rays, and cathode rays. This property is possessed by fluorspar, uranium glass, sulphide of calcium, and many other substances. It finds use in analytical instruments to detect or measure radiation, and in some commercial applications.