noun Physics, Chemistry.

  1. 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).
  2. the property possessed by a substance capable of such emission.
  3. the radiation so produced.


  1. physics
    1. 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
    2. such an emission of photons that ceases as soon as the bombarding radiation is discontinued
    3. such an emission of photons for which the average lifetime of the excited atoms and molecules is less than about 10 –8 seconds
  2. the radiation emitted as a result of fluorescenceCompare phosphorescence

1852, “glowing in ultraviolet light,” coined by English mathematician and physicist Sir George G. Stokes (1819-1903) from fluorspar (see fluorine), because in it he first noticed the phenomenon, + -escence, on analogy of phosphorescence.


  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.

  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.

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.

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