[floo-res-uhns, flaw-, floh-]
noun Physics, Chemistry.
the emission of radiation, especially of visible light, by a substance during exposure to external radiation, as light or x-rays. Compare phosphorescence ( def 1 ).
the property possessed by a substance capable of such emission.
the radiation so produced.

1852; fluor(spar) + -escence, on the model of opalescence, in reference to the mineral's newly discovered property

nonfluorescence, noun

florescence, fluorescence.
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World English Dictionary
fluorescence (ˌflʊəˈrɛsəns)
1.  physics
 a.  the emission of light or other radiation from atoms or molecules that are bombarded by particles, such as electrons, or by radiation from a separate source. The bombarding radiation produces excited atoms, molecules, or ions and these emit photons as they fall back to the ground state
 b.  such an emission of photons that ceases as soon as the bombarding radiation is discontinued
 c.  such an emission of photons for which the average lifetime of the excited atoms and molecules is less than about 10--8 seconds
2.  Compare phosphorescence the radiation emitted as a result of fluorescence
[C19: fluor + -escence (as in opalescence)]

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Word Origin & History

1852, "glowing in ultraviolet light," coined by Eng. mathematician and physicist Sir George G. Stokes (1819-1903) from fluorspar (see fluorine), because in it he first noticed the phenomenon, + ending -escence from opalescence, phosphorescence.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

fluorescence fluo·res·cence (flu-rěs'əns, flô-)

  1. The emission of electromagnetic radiation, especially of visible light, stimulated in a substance by the absorption of incident radiation and persisting only as long as the stimulating radiation is continued.

  2. The property of emitting such radiation.

fluo·res'cent adj.
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American Heritage
Science Dictionary
fluorescence   (fl-rěs'əns)  Pronunciation Key 
  1. The giving off of light by a substance when it is exposed to electromagnetic radiation, such as visible light or x-rays. As long as electromagnetic radiation continues to bombard the substance, electrons in the fluorescent material become excited but return very quickly to lower energy, giving off light, always of the same frequency. Fluorescent dyes are often used in microscopic imaging, where different dyes can penetrate and illuminate different parts of the sample being examined, helping to distinguish its structures. Compare phosphorescence.

  2. The light produced in this way.

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American Heritage
Cultural Dictionary

fluorescence definition

The emission of light from an object as a result of bombardment by other kinds of electromagnetic radiation, such as x-rays or ultraviolet rays. Fluorescent materials may appear one color when bathed in visible light and another color when exposed to other kinds of electromagnetic radiation.

Note: “Black light” depends on fluorescence for its effects.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Additional levels of security can be added by targeting fluorescence promoters
  to genes of particular purpose.
The gene produces a protein that gives the jellyfish a green fluorescence.
The secret: leveraging the fluorescence already present in white paper.
Under a fluorescence microscope, cancer cells caught in the device have an
  intense green halo.
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