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phos·pho·res·cence (fŏs'fə-rĕs'əns)  |
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A delayed luminescence, that is, a luminescence that persists after removal of the exciting source. It is sometimes called afterglow.
This original definition is rather imprecise, because the properties of the detector used will determine whether or not there is an observable persistence. There is no generally accepted rigorous definition or uniform usage of the term phosphorescence. In the literature of inorganic luminescent systems, some authors define phosphorescence as delayed luminescence whose persistence time decreases with increasing temperature. According to this usage, luminescence whose persistence time is independent of temperature is called fluorescence regardless of the length of the afterglow; a temperature-independent afterglow of long duration is called simply a slow fluorescence, which implies that the atomic or molecular transition involved is forbidden to a greater or lesser degree by the spectroscopic selection rules. The most common mechanism of phosphorescence in photoconductive inorganic systems, however, occurs when electrons or holes, set free by the excitation process and trapped at lattice defects, are expelled from their traps by the thermal energy in the system and recombine with oppositely charged carriers with the emission of light. See also Hole states in solids; Selection rules (physics).
In the organic literature the term phosphorescence is reserved for the forbidden luminescent transition from a metastable energy state M to the ground state G, while the afterglow corresponding to the M→ E→G process (where E is a higher energy state) is called delayed fluorescence. See also Fluorescence; Light; Luminescence.
| Dental Dictionary: phosphorescence |
The seeming ability to glow in the dark; occurs in substances that continue to emit light following exposure to and subsequent removal of a radiation source.
| Architecture: phosphorescence |
The emission of light as the result of the absorption of electromagnetic radiation; continues for a noticeable length of time after excitation.
| Columbia Encyclopedia: phosphorescence |
| Veterinary Dictionary: phosphorescence |
The emission of light without appreciable heat; it is characterized by the emission of absorbed light after a delay and at a considerably longer wavelength than that of the absorbed light. Caused by a number of bacteria, especially in seawater. One of them, Pseudomonas phosphorescens, may infect coldrooms via infected fish but does not constitute decomposition so that phosphorescent meat is still edible.
| Geological Glossary: Phosphorescence |
A luminescence emanating from substances that have been irradiated with ultraviolet light or x-rays, but persisting after the source of the stimulation has been removed (see
| Wikipedia: Phosphorescence |
Phosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur less often in certain materials, absorbed radiation may be re-emitted at a lower intensity for up to several hours.
The study of phosphorescent materials led to the discovery of radioactivity in 1896.
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In simple terms, phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in some cases the mechanism used for "glow-in-the-dark" materials which are "charged" by exposure to light. Unlike the relatively swift reactions in a common fluorescent tube, phosphorescent materials used for these materials absorb the energy and "store" it for a longer time as the processes required to re-emit the light occur less often.
Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, on the order of 10 nanoseconds. However, for light to be absorbed and emitted at these fast time scales, the energy of the photons involved (i.e. the wavelength of the light) must be carefully tuned according to the rules of quantum mechanics to match the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the absorbed photon energy undergoes an unusual intersystem crossing into an energy state of higher spin multiplicity (see term symbol), usually a triplet state. As a result, the energy can become trapped in the triplet state with only classically "forbidden" transitions available to return to the lower energy state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet lifetimes on the order of milliseconds. However, some compounds have triplet lifetimes up to minutes or even hours, allowing these substances to effectively store light energy in the form of very slowly degrading excited electron states. If the phosphorescent quantum yield is high, these substances will release significant amounts of light over long time scales, creating so-called "glow-in-the-dark" materials.
where S is a singlet and T a triplet whose subscripts denote states (0 is the ground state, and 1 the excited state). Transitions can also occur to higher energy levels, but the first excited state is denoted for simplicity.
Some examples of "glow-in-the-dark" materials do not glow because they are phosphorescent. For example, "glow sticks" glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemi-luminescence, an excited state is created via a chemical reaction. The excited state will then transfer to a "dye" molecule, also known as a sensitizer or fluorophor, and subsequently fluoresce back to the ground state.
Common pigments used in phosphorescent materials include zinc sulfide and strontium aluminate. Use of zinc sulfide for safety related products dates back to the 1930s. However, the development of strontium oxide aluminate, with a luminance approximately 10 times greater than zinc sulfide, has relegated most zinc sulfide based products to the novelty category. Strontium oxide aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage. Strontium aluminate based afterglow pigments are marketed under brandnames like Super-LumiNova[1][2] or NoctiLumina.[3]
 left: ZnS, right: aluminate |
 pigments in the dark |
 pigments in the dark after 4 min |
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Architecture. McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Geological Glossary. Peterson Field Guide to Rocks and Minerals, by Frederick H. Pough. Copyright © 1998 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Phosphorescence". Read more |
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