fluorescence

fluorescence , luminescence in which light of a visible color is emitted from a substance under stimulation or excitation by light or other forms of electromagnetic radiation or by certain other means. The light is given off only while the stimulation continues; in this the phenomenon differs from phosphorescence , in which light continues to be emitted after the excitation by other radiation has ceased. Fluorescence of certain rocks and other substances had been observed for hundreds of years before its nature was understood. Probably the first to explain it was the British scientist Sir George G. Stokes, who named the phenomenon after fluorite, a strongly fluorescent mineral. Stokes is credited with the discovery (1852) that fluorescence can be induced in certain substances by stimulation with ultraviolet light. He formulated Stokes's law, which states that the wavelength of the fluorescent light is always greater than that of the exciting radiation, but exceptions to this law have been found. Later it was discovered that certain organic and inorganic substances can be made to fluoresce by activation not only with ultraviolet light but also with visible light, infrared radiation, X rays, radio waves, cathode rays, friction, heat, pressure, and some other excitants. Fluorescent substances, sometimes also known as phosphors, are used in paints and coatings, but their chief use is in fluorescent lighting .

fluorescence Emission of radiation, usually light, from a substance when its atoms have acquired excess energy from a bombarding source of radiation, usually ultraviolet light or electrons. When the source of energy is removed, the fluorescence ceases. Mercury vapour is a fluorescent substance used in motorway lights; television tubes use fluorescent screens.

fluorescence (floo-er-ess-ĕns) n. the emission of light by a material as it absorbs radiation from outside. The radiation absorbed may be visible or invisible (e.g. ultraviolet rays or X-rays). See fluoroscope.
—fluorescent adj.