fluorescence

fluorescence
/floo res"euhns, flaw-, floh-/, n. Physics, Chem.
1. the emission of radiation, esp. of visible light, by a substance during exposure to external radiation, as light or x-rays. Cf. phosphorescence (def. 1).
2. the property possessed by a substance capable of such emission.
3. the radiation so produced.
[1852; FLUOR(SPAR) + -ESCENCE, on the model of OPALESCENCE, in reference to the mineral's newly discovered property]

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Emission of electromagnetic radiation, usually visible light, caused by excitation of atoms in a material, which then reemit almost immediately (within about 10-8 seconds).

The initial excitation is usually caused by absorption of energy from incident radiation or particles, such as X rays or electrons. Because re-emission occurs so quickly, the fluorescence ceases as soon as the exciting source is removed, unlike phosphorescence, which persists as an afterglow. A fluorescent lightbulb is coated on the inside with a powder and contains a gas; electricity causes the gas to emit ultraviolet radiation, which then stimulates the tube coating to emit light. The pixels of a television or computer screen fluoresce when electrons from an electron gun strike them. Fluorescence is often used to analyze molecules, and the addition of a fluorescing agent with emissions in the blue region of the spectrum to detergents causes fabrics to appear whiter in sunlight. X-ray fluorescence is used to analyze minerals.

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Universalium. 2010.

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