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Triplet phosphorescence occurs when an atom absorbs a high-energy photon, and the energy becomes locked in the spin multiplicity of the electrons, generally changing from a fluorescent "singlet state" to a slower emitting "triplet state". There are two, separate mechanisms that may produce phosphorescence, called triplet phosphorescence (or simply phosphorescence) and persistent phosphorescence (or persistent luminescence).
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Whereas fluorescent materials stop emitting light within nanoseconds (billionths of a second) after the excitation radiation is removed, phosphorescent materials may continue to emit an afterglow ranging from a few microseconds to many hours after the excitation is removed.
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In a modern, scientific sense, the phenomena can usually be classified by the three different mechanisms that produce the light, and the typical timescales during which those mechanisms emit light. In a general or colloquial sense, there is no distinct boundary between the emission times of fluorescence and phosphorescence (i.e.: if a substance glows under a black light it is generally considered fluorescent, and if it glows in the dark it is often simply called phosphorescent). Instead, a phosphorescent material absorbs some of the radiation energy and reemits it for a much longer time after the radiation source is removed. Unlike fluorescence, a phosphorescent material does not immediately reemit the radiation it absorbs. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Phosphorescence is a type of photoluminescence related to fluorescence. Phosphorescent, europium-doped, strontium silicate-aluminate oxide powder under visible light, fluorescing/phosphorescing under long-wave UV light, and persistently phosphorescing in total darkness