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Phosphorescence

Phosphorescent powder under visible light, ultraviolet light, and total darkness.

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. Image File history File links Question_book-3. ... Bioluminescence is the production and emission of visible light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy. ... Lightsticks Chemoluminescence (sometimes chemiluminescence) is the emission of light (luminescence) as the result of a chemical reaction. ... Image File history File links Download high resolution version (1320x580, 64 KB)An example of phosphorescence. ... Image File history File links Download high resolution version (1320x580, 64 KB)An example of phosphorescence. ... Photoluminescence is a process in which a chemical compound absorbs a photon (electromagnetic radiation), thus transitioning to a higher electronic energy state, and then radiates a photon back out, returning to a lower energy state. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ...

In simpler 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 subatomic reactions 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 quantum mechanically "forbidden" transitions available to return to the lower energy state. These transitions, although "forbidden", will still occur 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. In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... A photophysical process. ... In quantum mechanics, the term symbol is an abbreviated description of the angular momentum quantum numbers in a multi-electron atom. ... A diradical in organic chemistry is a molecular species with two electrons occupying two degenerate molecular orbitals (MO) of the same energy [1] [2]. They are known by their higher reactivities and shorter lifetimes. ... In physical chemistry, chemical kinetics or reaction kinetics is the study of reaction rates in a chemical reaction. ... The Quantum Yield of a radiation-induced process is the number of times that a defined event (usually a chemical reaction step) occurs per photon absorbed by the system. ...

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. Three types of lightsticks in several colours A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. ... Lightsticks Chemoluminescence (sometimes chemiluminescence) is the emission of light (luminescence) as the result of a chemical reaction. ... Sensitiser in chemoluminescence is a compound, capable of light emission after it has received energy from a molecule, which became excited previously in the chemical reaction. ... A fluorophor is a compound that emits light via fluorescence. ...

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. Zinc sulfide (or zinc sulphide) is a chemical compound with the formula ZnS. Zinc sulfide is a white to yellow colored powder or crystal. ... Strontium aluminate (SRA, SrAl, SrAl2O4) is a solid odorless nonflammable pale yellow powder, heavier than water. ...

The study of phosphorescent materials led to the discovery of radioactivity in 1896. Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ...

Equation

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. In theoretical physics, a singlet usually refers to a one-dimensional representation (e. ... In physics, spin is the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ...

Literature

• Phosphorescence is a recurrent symbol used by the writer D. H. Lawrence.

D. H. Lawrence David Herbert Lawrence (11 September 1885 - 2 March 1930) was one of the most important, certainly one of the most controversial, English writers of the 20th century, who wrote novels, short stories, poems, plays, essays, travel books, and letters. ...

See also

• Phosphor

Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ...

External links

Look up phosphorescence, glowing in Wiktionary, the free dictionary.

• Phosphorescence on Scienceworld
• The Cathode Ray Tube site
• Glow in the Dark Project Forum