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Fluorescence

(Science: chemistry, physics) The emission of one or more photons by a molecule or atom activated by the absorption of a quantum of electro magnetic radiation.

Typically the emission, that is of longer wavelength than the excitatory radiation, occurs within 10exp 8 seconds: phosphorescence is a phenomenon with a longer or much longer delay in re radiation. Note that rays, x-rays, uv, visible light and ir radiations may all stimulate fluorescence.