1.
Phosphorescent (band)
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Phosphorescent is the working moniker of American singer-songwriter, Matthew Houck. Originally from Alabama, Houck began recording and performing under this nom de plume in 2001 in Athens and he is currently based in Brooklyn, New York. Before recording under the name Phosphorescent, Matthew Houck traveled the world playing under the moniker Fillup Shack, Houck later changed his recording name to Phosphorescent, and released the full-length LP A Hundred Times or More in 2003. Notably, in the notes of A Hundred Times or More. The album was released through Athens-based independent label Warm Records, the following year, he released the EP The Weight of Flight. Phosphorescent rose to critical acclaim after releasing Aw Come Aw Wry in August 2005. The latter was named the 12th best album of 2007 by Stylus Magazine, in 2009, inspired by Willie Nelsons tribute album to Lefty Frizzell To Lefty From Willie, Houck crafted a tribute album to Nelson himself entitled, To Willie which was released through Dead Oceans. Phosphorescent released Heres to Taking It Easy in 2010, muchacho, Phosphorescents sixth studio album was released in 2013 to critical acclaim. The song Wolves from 2007s Pride was used in the 2011 film Margin Call, starring Kevin Spacey, the song Nothing Was Stolen from 2010s Heres to Taking It Easy was used in the 2012 film The Vow, starring Rachel McAdams and Channing Tatum. It is also used in season 1 episode 2 Signal and Noise of the television series Frequency, official website Ukulele Session by Noahm for Le Soir Phosphorescent, A Full-Grown Man
2.
Bioluminescence
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Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence, Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria and terrestrial invertebrates such as fireflies. In some animals, the light is produced by organisms such as Vibrio bacteria. The principal chemical reaction in bioluminescence involves the light-emitting pigment luciferin, the enzyme catalyzes the oxidation of luciferin. In some species, the type of luciferin requires cofactors such as calcium or magnesium ions, in evolution, luciferins vary little, one in particular, coelenterazine, is found in nine different animal, though in some of these, the animals obtain it through their diet. Conversely, luciferases vary widely in different species, Bioluminescence has arisen over forty times in evolutionary history. It was not until the nineteenth century that bioluminescence was properly investigated. The phenomenon is widely distributed among animal groups, especially in environments where dinoflagellates cause phosphorescence in the surface layers of water. On land it occurs in fungi, bacteria and some groups of invertebrates, in the laboratory, luciferase-based systems are used in genetic engineering and for biomedical research. Other researchers are investigating the possibility of using bioluminescent systems for street and decorative lighting, before the development of the safety lamp for use in coal mines, dried fish skins were used in Britain and Europe as a weak source of light. This experimental form of illumination avoided the necessity of using candles which risked sparking explosions of firedamp, another safe source of illumination in mines was bottles containing fireflies. In 1920, the American zoologist E. Newton Harvey published a monograph, The Nature of Animal Light, Harvey notes that Aristotle mentions light produced by dead fish and flesh, and that both Aristotle and Pliny the Elder mention light from damp wood. He also records that Robert Boyle experimented on these light sources, tuckey, in his posthumous 1818 Narrative of the Expedition to the Zaire, described catching the animals responsible for luminescence. He mentions pellucids, crustaceans, and cancers, under the microscope he described the luminous property to be in the brain, resembling a most brilliant amethyst about the size of a large pins head. Charles Darwin noticed bioluminescence in the sea, describing it in his Journal, While sailing in these latitudes on one very dark night, the sea presented a wonderful and most beautiful spectacle. There was a breeze, and every part of the surface. The vessel drove before her bows two billows of liquid phosphorus, and in her wake she was followed by a milky train. Darwin also observed a luminous jelly-fish of the genus Dianaea and noted that When the waves scintillate with bright green sparks, but there can be no doubt that very many other pelagic animals, when alive, are phosphorescent
3.
Chemiluminescence
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Chemiluminescence is the emission of light, as the result of a chemical reaction. There may also be limited emission of heat, the decay of this excited state to a lower energy level causes light emission. In theory, one photon of light should be given off for each molecule of reactant and this is equivalent to Avogadros number of photons per mole of reactant. In actual practice, non-enzymatic reactions seldom exceed 1% QC, quantum efficiency, in a chemical reaction, reactants collide to form a transition state, the enthalpic maximum in a reaction coordinate diagram, which proceeds to the product. Normally, reactants form products of chemical energy. The difference in energy between reactants and products, represented as Δ H r x n, is turned into heat, since vibrational energy is generally much greater than the thermal agitation, it rapidly disperses in the solvent through molecular rotation. This is how exothermic reactions make their solutions hotter, in a chemiluminescent reaction, the direct product of the reaction is an excited electronic state. Chemiluminescence differs from fluorescence or phosphorescence in that the excited state is the product of a chemical reaction rather than of the absorption of a photon. It is the antithesis of a reaction, in which light is used to drive an endothermic chemical reaction. Here, light is generated from an exothermic reaction. A standard example of chemiluminescence in the setting is the luminol test. Here, blood is indicated by luminescence upon contact with iron in hemoglobin, when chemiluminescence takes place in living organisms, the phenomenon is called bioluminescence. A light stick emits light by chemiluminescence, luminol in an alkaline solution with hydrogen peroxide in the presence of iron or copper, or an auxiliary oxidant, produces chemiluminescence. This is a reaction of phosphorus vapor, above the solid, with oxygen producing the excited states 2. Another gas phase reaction is the basis of nitric oxide detection in commercial analytic instruments applied to environmental air-quality testing, ozone is combined with nitric oxide to form nitrogen dioxide in an activated state. NO+O3 → NO2+ O2 The activated NO2 luminesces broadband visible to infrared light as it reverts to an energy state. A photomultiplier and associated electronics counts the photons that are proportional to the amount of NO present, the ozone reaction produces a photon count proportional to NO that is proportional to NO2 before it was converted to NO. In the case of a sample that contains both NO and NO2, the above reaction yields the amount of NO and NO2 combined in the air sample
4.
Europium
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Europium is a chemical element with symbol Eu and atomic number 63. It was isolated in 1901 and is named after the continent of Europe and it is a moderately hard, silvery metal which readily oxidizes in air and water. Being a typical member of the series, europium usually assumes the oxidation state +3. All europium compounds with oxidation state +2 are slightly reducing, Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds, Europium is one of the least abundant elements in the universe, only about 5×10−8% of all matter in the universe is europium. Europium is a metal with a hardness similar to that of lead. It crystallizes in a cubic lattice. Some properties of europium are strongly influenced by its half-filled electron shell, Europium has the second lowest melting point and the lowest density of all lanthanides. Europium becomes a superconductor when it is cooled below 1.8 K and this is because europium is divalent in the metallic state, and is converted into the trivalent state by the applied pressure. In the divalent state, the local magnetic moment suppresses the superconductivity. Europium is the most reactive rare earth element and it rapidly oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days. This behavior is unusual to most lanthanides, which almost exclusively form compounds with a state of +3. The +2 state has an electron configuration 4f7 because the half-filled f-shell gives more stability, in terms of size and coordination number, europium and barium are similar. For example, the sulfates of both barium and europium are also highly insoluble in water, divalent europium is a mild reducing agent, oxidizing in air to form Eu compounds. In anaerobic, and particularly geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths. This ion-exchange process is the basis of the europium anomaly. Bastnäsite tends to show less of a negative europium anomaly than does monazite, the development of easy methods to separate divalent europium from the other lanthanides made europium accessible even when present in low concentration, as it usually is. Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, while 153Eu is stable, 151Eu was recently found to be unstable to alpha decay with half-life of 5+11 −3×1018 years, giving about 1 alpha decay per two minutes in every kilogram of natural europium
5.
Strontium
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Strontium is a chemical element with symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically, the metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two neighbors in the periodic table, calcium and barium. It occurs naturally in the minerals celestine, strontianite, and putnisite, natural stable strontium, on the other hand, is not hazardous to health. Strontium was first isolated as a metal in 1808 by Humphry Davy using the then-newly discovered process of electrolysis, the production of sugar from sugar beet was in the 19th century the largest application of strontium. At the peak of production of cathode ray tubes, as much as 75 percent of strontium consumption in the United States was used for the faceplate glass. With the displacement of cathode ray tubes by other display methods, Strontium is a divalent silvery metal with a pale yellow tint whose properties are mostly intermediate between and similar to those of its group neighbors calcium and barium. It is softer than calcium and harder than barium and its melting and boiling points are lower than those of calcium, barium continues this downward trend in the melting point, but not in the boiling point. The density of strontium is similarly intermediate between those of calcium and barium, three allotropes of metallic strontium exist, with transition points at 235 and 540 °C. The standard electrode potential for the Sr2+/Sr couple is −2.89 V, Strontium is intermediate between calcium and barium in its reactivity toward water, with which it reacts on contact to produce strontium hydroxide and hydrogen gas. Strontium metal burns in air to produce both strontium oxide and strontium nitride, but since it does not react with nitrogen below 380 °C, at room temperature, it forms only the oxide spontaneously. Besides the simple oxide SrO, the peroxide SrO2 can be made by oxidation of strontium metal under a high pressure of oxygen. Strontium hydroxide, Sr2, is a base, though it is not as strong as the hydroxides of barium or the alkali metals. Due to the size of the heavy s-block elements, including strontium. Organostrontium compounds contain one or more strontium–carbon bonds and they have been reported as intermediates in Barbier-type reactions. Organostrontium compounds tend to be similar to organoeuropium or organosamarium compounds due to the similar ionic radii of these elements. Most of these compounds can only be prepared at low temperatures, because of its extreme reactivity with oxygen and water, this element occurs naturally only in compounds with other elements, such as in the minerals strontianite and celestine. It is kept under a liquid such as mineral oil or kerosene to prevent oxidation
6.
Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
7.
Fluorescence
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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. Fluorescent materials cease to glow immediately when the radiation source stops, unlike phosphorescence, Fluorescence also occurs frequently in nature in some minerals and in various biological states in many branches of the animal kingdom. An early observation of fluorescence was described in 1560 by Bernardino de Sahagún and it was derived from the wood of two tree species, Pterocarpus indicus and Eysenhardtia polystachya. The chemical compound responsible for this fluorescence is matlaline, which is the product of one of the flavonoids found in this wood. The name was derived from the fluorite, some examples of which contain traces of divalent europium. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight, the specific frequencies of exciting and emitted light are dependent on the particular system. S0 is called the state of the fluorophore, and S1 is its first excited singlet state. A molecule in S1 can relax by various competing pathways and it can undergo non-radiative relaxation in which the excitation energy is dissipated as heat to the solvent. Excited organic molecules can also relax via conversion to a triplet state, relaxation from S1 can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation, this phenomenon is known as the Stokes shift. The emitted radiation may also be of the wavelength as the absorbed radiation. Molecules that are excited through light absorption or via a different process can transfer energy to a second sensitized molecule, the fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed, Φ = Number of photons emitted Number of photons absorbed The maximum fluorescence quantum yield is 1.0, each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent, thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected. Fluorescence quantum yields are measured by comparison to a standard, the quinine salt quinine sulfate in a sulfuric acid solution is a common fluorescence standard. The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. This is an instance of exponential decay, various radiative and non-radiative processes can de-populate the excited state
8.
Energy level
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A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy and these discrete values are called energy levels. The energy spectrum of a system with discrete energy levels is said to be quantized. In chemistry and atomic physics, a shell, or a principal energy level. The closest shell to the nucleus is called the 1 shell, followed by the 2 shell, then the 3 shell, the shells correspond with the principal quantum numbers or are labeled alphabetically with letters used in the X-ray notation. Each shell can contain only a number of electrons, The first shell can hold up to two electrons, the second shell can hold up to eight electrons, the third shell can hold up to 18. The general formula is that the nth shell can in principle hold up to 2 electrons, since electrons are electrically attracted to the nucleus, an atoms electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a requirement, atoms may have two or even three incomplete outer shells. For an explanation of why electrons exist in these shells see electron configuration, if the potential energy is set to zero at infinite distance from the atomic nucleus or molecule, the usual convention, then bound electron states have negative potential energy. If an atom, ion, or molecule is at the lowest possible level, it. If it is at an energy level, it is said to be excited. If more than one quantum state is at the same energy. They are then called degenerate energy levels, quantized energy levels result from the relation between a particles energy and its wavelength. For a confined particle such as an electron in an atom, only stationary states with energies corresponding to integral numbers of wavelengths can exist, for other states the waves interfere destructively, resulting in zero probability density. Elementary examples that show mathematically how energy levels come about are the particle in a box, the first evidence of quantization in atoms was the observation of spectral lines in light from the sun in the early 1800s by Joseph von Fraunhofer and William Hyde Wollaston. The notion of levels was proposed in 1913 by Danish physicist Niels Bohr in the Bohr theory of the atom. The modern quantum mechanical theory giving an explanation of these levels in terms of the Schrödinger equation was advanced by Erwin Schrödinger and Werner Heisenberg in 1926. When the electron is bound to the atom in any closer value of n, assume there is one electron in a given atomic orbital in a hydrogen-like atom
9.
Quantum mechanics
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Quantum mechanics, including quantum field theory, is a branch of physics which is the fundamental theory of nature at small scales and low energies of atoms and subatomic particles. Classical physics, the physics existing before quantum mechanics, derives from quantum mechanics as an approximation valid only at large scales, early quantum theory was profoundly reconceived in the mid-1920s. The reconceived theory is formulated in various specially developed mathematical formalisms, in one of them, a mathematical function, the wave function, provides information about the probability amplitude of position, momentum, and other physical properties of a particle. In 1803, Thomas Young, an English polymath, performed the famous experiment that he later described in a paper titled On the nature of light. This experiment played a role in the general acceptance of the wave theory of light. In 1838, Michael Faraday discovered cathode rays, Plancks hypothesis that energy is radiated and absorbed in discrete quanta precisely matched the observed patterns of black-body radiation. In 1896, Wilhelm Wien empirically determined a distribution law of black-body radiation, ludwig Boltzmann independently arrived at this result by considerations of Maxwells equations. However, it was only at high frequencies and underestimated the radiance at low frequencies. Later, Planck corrected this model using Boltzmanns statistical interpretation of thermodynamics and proposed what is now called Plancks law, following Max Plancks solution in 1900 to the black-body radiation problem, Albert Einstein offered a quantum-based theory to explain the photoelectric effect. Among the first to study quantum phenomena in nature were Arthur Compton, C. V. Raman, robert Andrews Millikan studied the photoelectric effect experimentally, and Albert Einstein developed a theory for it. In 1913, Peter Debye extended Niels Bohrs theory of structure, introducing elliptical orbits. This phase is known as old quantum theory, according to Planck, each energy element is proportional to its frequency, E = h ν, where h is Plancks constant. Planck cautiously insisted that this was simply an aspect of the processes of absorption and emission of radiation and had nothing to do with the reality of the radiation itself. In fact, he considered his quantum hypothesis a mathematical trick to get the right rather than a sizable discovery. He won the 1921 Nobel Prize in Physics for this work, lower energy/frequency means increased time and vice versa, photons of differing frequencies all deliver the same amount of action, but do so in varying time intervals. High frequency waves are damaging to human tissue because they deliver their action packets concentrated in time, the Copenhagen interpretation of Niels Bohr became widely accepted. In the mid-1920s, developments in mechanics led to its becoming the standard formulation for atomic physics. In the summer of 1925, Bohr and Heisenberg published results that closed the old quantum theory, out of deference to their particle-like behavior in certain processes and measurements, light quanta came to be called photons
10.
Radioactive decay
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A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, however, for a collection of atoms, the collections expected decay rate is characterized in terms of their measured decay constants or half-lives. This is the basis of radiometric dating, the half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitude, from nearly instantaneous to far longer than the age of the universe. A radioactive nucleus with spin can have no defined orientation. If there are multiple particles produced during a single decay, as in decay, their relative angular distribution. Such a parent process could be a previous decay, or a nuclear reaction, the decaying nucleus is called the parent radionuclide, and the process produces at least one daughter nuclide. Except for gamma decay or internal conversion from an excited state. When the number of changes, an atom of a different chemical element is created. The first decay processes to be discovered were alpha decay, beta decay, alpha decay occurs when the nucleus ejects an alpha particle. This is the most common process of emitting nucleons, but highly excited nuclei can eject single nucleons, or in the case of cluster decay, specific light nuclei of other elements. Beta decay occurs when the nucleus emits an electron or positron, the nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. All of these result in a well-defined nuclear transmutation. By contrast, there are radioactive decay processes that do not result in a nuclear transmutation, another type of radioactive decay results in products that vary, appearing as two or more fragments of the original nucleus with a range of possible masses. For a summary table showing the number of stable and radioactive nuclides in each category, there are 29 naturally occurring chemical elements on Earth that are radioactive. They are those that contain 34 radionuclides that date before the time of formation of the solar system, well-known examples are uranium and thorium, but also included are naturally occurring long-lived radioisotopes, such as potassium-40. Radioactivity was discovered in 1896 by the French scientist Henri Becquerel and these materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it, all results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper and these radiations were given the name Becquerel Rays
11.
Jablonski diagram
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A Jablonski diagram is a diagram that illustrates the electronic states of a molecule and the transitions between them. The states are arranged vertically by energy and grouped horizontally by spin multiplicity, nonradiative transitions are indicated by squiggly arrows and radiative transitions by straight arrows. The vibrational ground states of each state are indicated with thick lines. The diagram is named after the Polish physicist Aleksander Jabłoński, radiative transitions involve the absorption, if the transition occurs to a higher energy level, or the emission, in the reverse case, of a photon. Nonradiative transitions arise through several different mechanisms, all differently labeled in the diagram, relaxation of the excited state to its lowest vibrational level is called Vibrational relaxation. This process involves the dissipation of energy from the molecule to its surroundings, a third type is intersystem crossing, this is a transition to a state with a different spin multiplicity. In molecules with large spin-orbit coupling, intersystem crossing is more important than in molecules that exhibit only small spin-orbit coupling. This type of transition can give rise to phosphorescence. Spectroscopy Franck–Condon principle Grotrian diagram Florida State University, Jablonski diagram primer
12.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
13.
Intersystem crossing
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Intersystem crossing is a radiationless process involving a transition between two electronic states with different spin multiplicity. When an electron in a molecule with a ground state is excited to a higher energy level. A singlet state is an electronic state such that all electron spins are paired. That is, the spin of the electron is still paired with the ground state electron. In a triplet state the excited electron is no longer paired with the ground state electron, since excitation to a triplet state involves an additional forbidden spin transition, it is less probable that a triplet state will form when the molecule absorbs radiation. When a singlet state nonradiatively passes to a state, or conversely a triplet transitions to a singlet. In essence, the spin of the electron is reversed. The probability of this occurring is more favorable when the vibrational levels of the two excited states overlap, since little or no energy must be gained or lost in the transition. As the spin/orbital interactions in such molecules are substantial and a change in spin is more favourable. This process is called spin-orbit coupling, simply-stated, it involves coupling of the electron spin with the orbital angular momentum of non-circular orbits. In addition, the presence of species in solution enhances intersystem crossing. The radiative decay from an excited triplet state back to a state is known as phosphorescence. Since a transition in spin multiplicity occurs, phosphorescence is a manifestation of intersystem crossing, the time scale of intersystem crossing is on the order of 10−8 to 10−3 s, one of the slowest forms of relaxation
14.
Chemical kinetics
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Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Van t Hoff studied chemical dynamics and published in 1884 his famous Etudes de dynamique chimique, after van t Hoff, chemical kinetics deals with the experimental determination of reaction rates from which rate laws and rate constants are derived. Relatively simple rate laws exist for zero order reactions, first order reactions, and second order reactions, and can be derived for others. Elementary reactions follow the law of action, but the rate law of stepwise reactions has to be derived by combining the rate laws of the various elementary steps. In consecutive reactions, the rate-determining step often determines the kinetics, in consecutive first order reactions, a steady state approximation can simplify the rate law. The activation energy for a reaction is determined through the Arrhenius equation. Gorban and Yablonsky have suggested that the history of chemical dynamics can be divided into three eras, the first is the van t Hoff wave searching for the general laws of chemical reactions and relating kinetics to thermodynamics. The second may be called the Semenov--Hinshelwood wave with emphasis on reaction mechanisms, the third is associated with Aris and the detailed mathematical description of chemical reaction networks. Depending upon what substances are reacting, the rate varies. Acid/base reactions, the formation of salts, and ion exchange are fast reactions, when covalent bond formation takes place between the molecules and when large molecules are formed, the reactions tend to be very slow. Nature and strength of bonds in reactant molecules greatly influence the rate of its transformation into products, the physical state of a reactant is also an important factor of the rate of change. When reactants are in the phase, as in aqueous solution. However, when they are in different phases, the reaction is limited to the interface between the reactants, reaction can occur only at their area of contact, in the case of a liquid and a gas, at the surface of the liquid. Vigorous shaking and stirring may be needed to bring the reaction to completion and this means that the more finely divided a solid or liquid reactant the greater its surface area per unit volume and the more contact it with the other reactant, thus the faster the reaction. To make an analogy, for example, when one starts a fire, one uses wood chips, in organic chemistry, on water reactions are the exception to the rule that homogeneous reactions take place faster than heterogeneous reactions. In a solid, only those particles that are at the surface can be involved in a reaction, for example, Sherbet is a mixture of very fine powder of malic acid and sodium hydrogen carbonate. On contact with the saliva in the mouth, these chemicals quickly dissolve and react, releasing carbon dioxide, also, fireworks manufacturers modify the surface area of solid reactants to control the rate at which the fuels in fireworks are oxidised, using this to create different effects. For example, finely divided aluminium confined in a shell explodes violently, if larger pieces of aluminium are used, the reaction is slower and sparks are seen as pieces of burning metal are ejected
15.
Glow stick
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A glow stick is a self-contained, short-term light-source. It consists of a translucent plastic tube containing isolated substances that, the light cannot be turned off and can only be used once. Glow sticks are used for recreation, but may also be relied upon for light during military, police, fire. Bisoxalate, trademarked Cyalume, was invented by Michael M. Rauhut and Laszlo J. Bollyky of American Cyanamid, other early work on chemiluminescence was carried out at the same time, by researchers under Herbert Richter at China Lake Naval Weapons Center. Several US patents for glow stick type devices were received by various inventors, bernard Dubrow and Eugene Daniel Guth patented a Packaged Chemiluminescent Material in June 1965. In October 1973, Clarence W. Gilliam, David Iba Sr. in June 1974 a patent for a Chemiluminescent Device was issued with Herbert P. Richter and Ruth E. Tedrick listed as the inventors. In January 1976, a patent was issued for the Chemiluminescent Signal Device, with Vincent J. Esposito, Steven M. Little and this patent recommended a single glass ampoule that is suspended in a second substance, that when broken and mixed together, provide the chemiluminescent light. The design also included a stand for the device so it could be thrown from a moving vehicle. In December 1977 a patent was issued for a Chemical Light Device with Richard Taylor Van Zandt as the inventor, glow sticks are waterproof, do not use batteries, generate negligible heat, are inexpensive, and are reasonably disposable. They can tolerate high pressures, such as found under water. They are used as sources and light markers by military forces, campers. Glow sticks are considered the light source that is safe for use immediately following any catastrophic event. Glowsticking is the use of sticks in dancing. This is one of their most widely known uses in popular culture, as they are used for entertainment at parties, concerts. They are used by marching band conductors for evening performances, glow sticks are used in festivals. Glow sticks also serve multiple functions as toys, readily visible night-time warnings to motorists, yet another use is for balloon-carried light effects. Glow sticks are used to create special effects in low light photography. The Guinness Book of Records says the worlds largest glow stick was cracked at 9 ft 10 in tall and it was created using Plexiglass by KNIXS GmbH in Darmstadt Weiterstadt, Germany, on 29 June 2009
16.
Photoelectrochemical process
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Photoelectrochemical processes are processes in photoelectrochemistry, they usually involve transforming light into other forms of energy. These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, electron excitation is the movement of an electron to a higher energy state. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to move electrons to an energy band. When an excited electron falls back to an energy state again. This can be done by radiation of a photon or giving the energy to a third spectator particle as well, in physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state. The excited state, in general, is in relation to the ground state, photoexcitation is the mechanism of electron excitation by photon absorption, when the energy of the photon is too low to cause photoionization. The absorption of the takes place in accordance with Plancks quantum theory. Photoexcitation is exploited in dye-sensitized solar cells, photochemistry, luminescence, optically pumped lasers, in chemistry, photoisomerization is molecular behavior in which structural change between isomers is caused by photoexcitation. Both reversible and irreversible photoisomerization reactions exist, however, the word photoisomerization usually indicates a reversible process. Photoisomerizable molecules are already put to use, for instance, in pigments for rewritable CDs, DVDs. In addition, recent interest in photoisomerizable molecules has been aimed at molecular devices, such as switches, molecular motors. Photoisomerization behavior can be categorized into several classes. Two major classes are trans-cis conversion, and open-closed ring transition, examples of the former include stilbene and azobenzene. This type of compounds has a bond, and rotation or inversion around the double bond affords isomerization between the two states. Examples of the latter include fulgide and diarylethene and this type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light. Still another class is the Di-pi-methane rearrangement, Photoionization is the physical process in which an incident photon ejects one or more electrons from an atom, ion or molecule. This is essentially the process that occurs with the photoelectric effect with metals. In the case of a gas or single atoms, the term photoionization is more common, the ejected electrons, known as photoelectrons, carry information about their pre-ionized states
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Fluorophore
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A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds, fluorophores are sometimes used alone, as a tracer in fluids, as a dye for staining of certain structures, as a substrate of enzymes, or as a probe or indicator. More generally they are bonded to a macromolecule, serving as a marker for affine or bioactive reagents. Fluorophores are notably used to stain tissues, cells, or materials in a variety of methods, i. e. fluorescent imaging. Fluorescein, by its amine reactive isothiocyanate derivative FITC, has one of the most popular fluorophores. From antibody labeling, the applications have spread to nucleic acids thanks to, other historically common fluorophores are derivatives of rhodamine, coumarin, and cyanine. The fluorophore absorbs light energy of a wavelength and re-emits light at a longer wavelength. Wavelengths of maximum absorption and emission are the terms used to refer to a given fluorophore. The excitation wavelength spectrum may be a narrow or broader band. The emission spectrum is usually sharper than the spectrum, and it is of a longer wavelength. Excitation energies range from ultraviolet through the spectrum, and emission energies may continue from visible light into the near infrared region. Quantum yield, efficiency of the transferred from incident light to emitted fluorescence Lifetime. It refers to the time taken for a population of excited fluorophores to decay to 1/e of the original amount, stokes shift, difference between the maximum excitation and maximum emission wavelengths. These characteristics drive other properties, including the photobleaching or photoresistance, other parameters should be considered, as the polarity of the fluorophore molecule, the fluorophore size and shape, and other factors can change the behavior of fluorophores. Fluorophores can also be used to quench the fluorescence of other fluorescent dyes or to relay their fluorescence at longer wavelength See more on fluorescence principle. Fluorescence particles are not considered fluorophores, the size of the fluorophore might sterically hinder the tagged molecule, and affect the fluorescence polarity. Fluorophore molecules could be either utilized alone, or serve as a fluorescent motif of a functional system, fluorescent proteins GFP, YFP and RFP can be attached to other specific proteins to form a fusion protein, synthesized in cells after transfection of a suitable plasmid carrier. Oxazine derivatives, Nile red, Nile blue, cresyl violet, oxazine 170, acridine derivatives, proflavin, acridine orange, acridine yellow, etc
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Zinc sulfide
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Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is black because of various impurities, the pure material is white. In its dense synthetic form, zinc sulfide can be transparent, ZnS exists in two main crystalline forms, and this dualism is often a salient example of polymorphism. In each form, the geometry at Zn and S is tetrahedral. The more stable form is known also as zinc blende or sphalerite. The hexagonal form is known as the mineral wurtzite, although it also can be produced synthetically, the transition from the sphalerite form to the wurtzite form occurs at around 1020 celsius. When silver is used as activator, the color is bright blue. Using manganese yields a color at around 590 nanometers. Copper gives long-time glow, and it has the familiar greenish glow-in-the-dark, copper-doped zinc sulfide is used also in electroluminescent panels. It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light, zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to just over 12 micrometers. It can be used planar as a window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from hydrogen gas and zinc vapour, and this is sold as FLIR-grade. This material when hot isostatically pressed can be converted to a form known as Cleartran. Early commercial forms were marketed as Irtran-2 but this designation is now obsolete, zinc sulfide is a common pigment, sometimes called sachtolith. When combined with barium sulfate, zinc sulfide forms lithopone, fine ZnS powder is an efficient photocatalyst, which produces hydrogen gas from water upon illumination. Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors and these are prototypical II-VI semiconductors, and they adopt structures related to many of the other semiconductors, such as gallium arsenide. The cubic form of ZnS has a gap of about 3.54 electron volts at 300 kelvin
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Strontium aluminate
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Strontium aluminate is a solid odorless, nonflammable, pale yellow, monoclinic crystalline powder, heavier than water. It is chemically and biologically inert, when activated with a suitable dopant, it acts as a photoluminescent phosphor with long persistence of phosphorescence. There are also other strontium aluminates, e. g. SrAl4O7, Sr3Al2O6, SrAl12O19 and it is frequently used in glow in the dark toys, where it displaces the cheaper but less efficient ZnS, Cu. However, the material has high hardness, causing abrasion to the handling it. Different aluminates can be used as the host matrix and this influences the wavelength of emission of the europium ion, by its covalent interaction with surrounding oxygens, and crystal field splitting of the 5d orbital energy levels. Strontium aluminate phosphors produce green and aqua hues, where gives the highest brightness. The excitation wavelengths for strontium aluminate range from 200 to 450 nm, the wavelength for its green formulation is 520 nm, its blue-green version emits at 505 nm, and the blue one emits at 490 nm. Colors with longer wavelengths can be obtained from the strontium aluminate as well, for europium-dysprosium doped aluminates, the peak emission wavelengths are 520 nm for SrAl2O4,480 nm for SrAl4O7, and 400 nm for SrAl12O19. SrAl2O4, Eu2+, Dy3+ is important as a persistently luminiscent phosphor for industrial applications and it can be produced by molten salt assisted process at 900 °C. The most described kind is the stoichiometric green-emitting SrAl2O4, Eu2+, SrAl2O4, Eu2+, Dy3+, B3+ shows significantly longer afterglow than the europium-only doped material. The Eu2+ dopant shows high afterglow, while Eu3+ has almost none, polycrystalline SrAl12O19, Mn is used as a green phosphor for plasma displays, and when doped with praseodymium or neodymium it can act as a good active laser medium. Sr0. 95Ce0. 05Mg0. 05Al11. 95O19 is a phosphor emitting at 305 nm, several strontium aluminates can be prepared by the sol-gel process. The wavelengths produced depend on the crystal structure of the material. Slight modifications in the process can significantly influence the emission wavelengths. Strontium aluminate phosphor is usually fired at about 1250 °C, though temperatures are possible. Subsequent exposure to temperatures above 1090 °C is likely to cause loss of its phosphorescent properties, at higher firing temperatures, the Sr3Al2O6 undergoes transformation to SrAl2O4. The glow intensity depends on the size, generally, the bigger the particles. Strontium aluminate based pigments are marketed under brand names like Art N Glow, Core Glow
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Flashtube
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A flashtube, also called a flashlamp, is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations. Flashtubes are made of a length of tubing with electrodes at either end and are filled with a gas that. Flashtubes are used mostly for photographic purposes but are employed in scientific, medical, industrial. The lamp comprises a hermetically sealed tube, which is filled with a noble gas, usually xenon. Additionally, a high power source is necessary to energize the gas as a trigger event. A charged capacitor is used to supply energy for the flash. In some applications, the emission of light is undesired, whether due to production of ozone, damage to laser rods, degradation of plastics. In these cases, a fused silica is used. A better alternative is a cerium-doped quartz, it does not suffer from solarization and has higher efficiency and its cutoff is at about 380 nm. The power level of the lamps is rated in watts/area, total electrical input power divided by the inner wall surface. Cooling of the electrodes and the envelope is of high importance at high power levels. Air cooling is sufficient for lower power levels. High power lamps are cooled with a liquid, typically by flowing demineralized water through a tube in which the lamp is encased, water-cooled lamps will generally have the glass shrunk around the electrodes, to provide a direct thermal conductor between them and the cooling water. The cooling medium should flow also across the length of the lamp. Above 15 W/cm2 forced air cooling is required, liquid cooling if in a confined space, liquid cooling is generally necessary above 30 W/cm2. For this reason, thinner glass is used for continuous-wave arc-lamps. Thicker materials can generally handle more impact energy from the wave that a short-pulsed arc can generate. The material of the envelope provides another limit for the power,1 mm thick fused quartz has a limit of 200 W/cm2
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Fused quartz
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Fused quartz or fused silica is glass consisting of silica in amorphous form. It differs from traditional glasses in containing no other ingredients, which are added to glass to lower the melt temperature. Fused silica, therefore, has high working and melting temperatures, the optical and thermal properties of fused quartz are superior to those of other types of glass due to its purity. For these reasons, it use in situations such as semiconductor fabrication. It has better ultraviolet transmission than most other glasses, and so is used to make lenses and its low coefficient of thermal expansion also makes it a useful material for precision mirror substrates. Fused quartz is produced by fusing high-purity silica sand, which consists of quartz crystals, quartz contains only silicon and oxygen, although commercial quartz glass often contains impurities. The most dominant impurities are aluminium and titanium, melting is effected at approximately 1650 °C using either an electrically heated furnace or a gas/oxygen-fuelled furnace. This results in a transparent glass with a purity and improved optical transmission in the deep ultraviolet. Fused quartz is normally transparent, the process of fusion results in a material that is translucent, the material can however appear opaque owing to the presence of small air bubbles trapped within the material. The water content is determined by the manufacturing process, flame fused material always has a higher water content due to the combination of the hydrocarbons and oxygen fuelling the furnace forming hydroxyl groups within the material. An IR grade material typically has an content of <10 parts per million, most of the applications of fused silica exploit its wide transparency range, which extends from the UV to the near IR. Fused silica is the key starting material for optical fiber, used for telecommunications, vacuum tubes with silica envelopes allowed for radiation cooling by incandescent anodes. Because of its strength fused silica was used in deep diving vessels such as the Bathysphere, the combination of strength, thermal stability, and UV transparency makes it an excellent substrate for projection masks for photolithography. EPROMs are recognizable by the transparent fused quartz window which sits on top of the package, through which the chip is visible. Due to the stability and composition it is used in semiconductor fabrication furnaces. Fused quartz has nearly ideal properties for fabricating first surface mirrors such as used in telescopes. The material behaves in a way and allows the optical fabricator to put a very smooth polish onto the surface and produce the desired figure with fewer testing iterations. These lenses are used for UV photography, as the glass has a lower extinction rate than lens made with more common flint or crown glass formulas
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Air-gap flash
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An air-gap flash is a photographic light source capable of producing sub-microsecond light flashes, allowing for high-speed photography. This is achieved by an electric discharge between two electrodes over the surface of a quartz tube. The distance between the electrodes is such that a discharge does not occur. To start the discharge a high-voltage pulse is applied on an electrode inside the quartz tube, the flash can be triggered electronically by being synchronised with an electronic detection device such as a microphone or an interrupted laser beam in order to illuminate a fast event. A sub-microsecond flash is fast enough to stop even a supersonic bullet in flight without noticeable motion blur. The person credited with popularising the flash is Harold Eugene Edgerton, william Henry Fox Talbot is said to have created the first spark-based flash photo, using a Leyden jar, the original form of the capacitor. Edgerton was one of the founders of EG&G company who sold an air-gap flash under the name Microflash 549, there are several commercial flashes available today. The aim of a flash is to be very fast. An air-gap flash system typically consists of a capacitor that is discharged through a gas, the speed of a flash is mainly determined by the time it takes to discharge the capacitor through the gas. This time is proportional to t d i s c h a r g e ∝ L C, in which L is the inductance, to be fast, both L and C must be kept small. The brightness of the flash is proportional to the energy stored in the capacitor, E = C V22 and this shows that high brightness calls for a large capacitance and a high voltage. Typical values are 0.05 µF capacitance,0.02 µH inductance,10 J energy,0.5 µs duration, air is preferred as a gas because it is fast. Xenon has a higher efficiency in turning energy into light. The spark is guided over a surface to improve the light output and benefit from the cooling capacity. This has an effect in the form of quartz erosion because of high energy discharge. Since the spark gap discharges in air generating a plasma, the spectrum shows both a continuum and spectral lines, mainly of nitrogen since air is 79% nitrogen, the spectrum is rich in UV but covers the entire visible range down to infra-red. When a quartz tube is used as ignition tube, it shows a clear phosphorescence in blue after the flash, amateur air-gap flash for ultra-high-speed photography by Niels Noordhoek MIT Edgerton center Scientific American article on air-gap flash
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Luminous paint
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Luminous paint or luminescent paint is paint that exhibits luminescence. In other words, it gives off light through fluorescence, phosphorescence. Fluorescent paints offer a range of pigments and chroma which also glow when exposed to the long-wave ultraviolet frequencies. These UV frequencies are found in sunlight and some artificial lights, human eyes perceive these changes as the unusual glow of fluorescence. The fluorescent type of luminescence is different from the natural bio-luminescence of bacteria, insects and fish such as the case of the firefly. Bio-luminescence involves no reflection at all, but living generation of light, there are both visible and invisible fluorescent paints. The visible appear under white light to be any bright color, invisible fluorescent paints appear transparent or pale under daytime lighting, but will glow under UV light in a limited range of colors. Since these can seem to disappear, they can be used to create a variety of clever effects, both types of fluorescent painting benefit when used within a contrasting ambiance of clean, matte-black backgrounds and borders. Such a black out effect will minimize other awareness, so cultivating the peculiar luminescence of UV fluorescence, both types of paints have extensive application where artistic lighting effects are desired, particularly in black box entertainments and environments such as theaters, bars, shrines, etc. Out-of-doors, however, UV wavelengths are scattered in space or absorbed by complex natural surfaces. Furthermore, the complex pigments will degrade quickly in sunlight, phosphorescent paint is commonly called glow-in-the-dark paint. It is made from such as silver-activated zinc sulfide or doped strontium aluminate. The mechanism for producing light is similar to that of fluorescent paint, phosphorescent paints have a sustained glow which lasts for up to 12 hours after exposure to light, fading over time. This type of paint has been used to mark escape paths in aircraft and for use such as stars applied to walls. It is an alternative to radioluminescent paint, kenners Lightning Bug Glo-Juice was a popular non-toxic paint product in 1968, marketed at children, alongside other glow-in-the-dark toys and novelties. When applied as a paint or a more sophisticated coating, phosphorescence can be used for detection or degradation measurements known as phosphor thermometry. Radioluminescent paint contains a radioactive isotope combined with a radioluminescent substance, the isotopes selected are typically strong emitters of fast electrons, preferred since this radiation will not penetrate an enclosure. Radioluminescent paints will glow without exposure to light until the radioactive isotope has decayed and they are therefore sometimes referred to as self-luminous
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Phosphor
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A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness, and fluorescent materials, where the emission decay takes place over tens of nanoseconds, Phosphors are often transition metal compounds or rare earth compounds of various types. The most common uses of phosphors are in CRT displays and fluorescent lights, CRT phosphors were standardized beginning around World War II and designated by the letter P followed by a number. Phosphorus, the element named for its light-emitting behavior, emits light due to chemiluminescence. A material can emit light either through incandescence, where all atoms radiate, or by luminescence, in inorganic phosphors, these inhomogeneities in the crystal structure are created usually by addition of a trace amount of dopants, impurities called activators. The wavelength emitted by the center is dependent on the atom itself. The scintillation process in inorganic materials is due to the band structure found in the crystals. An incoming particle can excite an electron from the band to either the conduction band or the exciton band. This leaves a hole behind, in the valence band. Impurities create electronic levels in the forbidden gap, the excitons are loosely bound electron-hole pairs that wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light, in case of inorganic scintillators, the activator impurities are typically chosen so that the emitted light is in the visible range or near-UV where photomultipliers are effective. The holes associated with electrons in the band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons, the delayed de-excitation of those metastable impurity states, slowed down by reliance on the low-probability forbidden mechanism, again results in light emission. Many phosphors tend to lose efficiency gradually by several mechanisms, the degradation of electroluminescent devices depends on frequency of driving current, the luminance level, and temperature, moisture impairs phosphor lifetime very noticeably as well. Harder, high-melting, water-insoluble materials display lower tendency to lose luminescence under operation, examples, BaMgAl10O17, Eu2+, a plasma display phosphor, undergoes oxidation of the dopant during baking. Thin coating of aluminium phosphate or lanthanum phosphate is effective in creation a barrier layer blocking access of oxygen to the BAM phosphor, for the cost of reduction of phosphor efficiency. Addition of hydrogen, acting as an agent, to argon in the plasma displays significantly extends the lifetime of BAM, Eu2+ phosphor. Y2O3, Eu phosphors under electron bombardment in presence of oxygen form a non-phosphorescent layer on the surface, the traps also damage the crystal lattice
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Phosphoroscope
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A phosphoroscope is piece of experimental equipment devised in 1857 by physicist A. E. Becquerel to measure how long it takes a phosphorescent material to stop glowing after it has been excited. It consists of two rotating disks with holes in them, the holes are placed on each disk at equal angled radial lines and a given distance from the centre but they do not align with each other. A sample of phosphorescent material is placed in between the two disks, light coming in through a hole in one of the discs excites the phosphorescent material which then emits light for a short amount of time. The disks are rotated and by changing their speed the length of time the material glows can be determined. Description and image of a phosphoroscope at the Kenyon College Department of Physics
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Tritium
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Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons, naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays. It can be produced by irradiating lithium metal or lithium bearing ceramic pebbles in a nuclear reactor, the name of this isotope is derived from the Greek word τρίτος meaning third. While tritium has several different experimentally determined values of its half-life and it decays into helium-3 by beta decay as in this nuclear equation, and it releases 18.6 keV of energy in the process. The electrons kinetic energy varies, with an average of 5.7 keV, beta particles from tritium can penetrate only about 6.0 mm of air, and they are incapable of passing through the dead outermost layer of human skin. The unusually low energy released in the beta decay makes the decay appropriate for absolute neutrino mass measurements in the laboratory. The low energy of tritiums radiation makes it difficult to detect tritium-labeled compounds except by using liquid scintillation counting, Tritium is produced in nuclear reactors by neutron activation of lithium-6. This is possible with neutrons of any energy, and is an exothermic reaction yielding 4.8 MeV, in comparison, the fusion of deuterium with tritium releases about 17.6 MeV of energy. High-energy neutrons can produce tritium from lithium-7 in an endothermic reaction. This was discovered when the 1954 Castle Bravo nuclear test produced a high yield. High-energy neutrons irradiating boron-10 will also produce tritium, A more common result of boron-10 neutron capture is 7Li. The reactions requiring high neutron energies are not attractive production methods for peaceful applications, Tritium is also produced in heavy water-moderated reactors whenever a deuterium nucleus captures a neutron. This reaction has a quite small absorption cross section, making water a good neutron moderator. Even so, cleaning tritium from the moderator may be desirable after several years to reduce the risk of its escaping to the environment. Ontario Power Generations Tritium Removal Facility processes up to 2,500 tonnes of water a year. Deuteriums absorption cross section for thermal neutrons is about 0.52 millibarns, whereas that of oxygen-16 is about 0.19 millibarns and that of oxygen-17 is about 240 millibarns. Tritium is a product of the nuclear fission of uranium-235, plutonium-239. The release or recovery of tritium needs to be considered in the operation of reactors, especially in the reprocessing of nuclear fuels
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National Diet Library
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The National Diet Library is the only national library in Japan. It was established in 1948 for the purpose of assisting members of the National Diet of Japan in researching matters of public policy, the library is similar in purpose and scope to the United States Library of Congress. The National Diet Library consists of two facilities in Tokyo and Kyoto, and several other branch libraries throughout Japan. The Diets power in prewar Japan was limited, and its need for information was correspondingly small, the original Diet libraries never developed either the collections or the services which might have made them vital adjuncts of genuinely responsible legislative activity. Until Japans defeat, moreover, the executive had controlled all political documents, depriving the people and the Diet of access to vital information. The U. S. occupation forces under General Douglas MacArthur deemed reform of the Diet library system to be an important part of the democratization of Japan after its defeat in World War II. In 1946, each house of the Diet formed its own National Diet Library Standing Committee, hani Gorō, a Marxist historian who had been imprisoned during the war for thought crimes and had been elected to the House of Councillors after the war, spearheaded the reform efforts. Hani envisioned the new body as both a citadel of popular sovereignty, and the means of realizing a peaceful revolution, the National Diet Library opened in June 1948 in the present-day State Guest-House with an initial collection of 100,000 volumes. The first Librarian of the Diet Library was the politician Tokujirō Kanamori, the philosopher Masakazu Nakai served as the first Vice Librarian. In 1949, the NDL merged with the National Library and became the national library in Japan. At this time the collection gained a million volumes previously housed in the former National Library in Ueno. In 1961, the NDL opened at its present location in Nagatachō, in 1986, the NDLs Annex was completed to accommodate a combined total of 12 million books and periodicals. The Kansai-kan, which opened in October 2002 in the Kansai Science City, has a collection of 6 million items, in May 2002, the NDL opened a new branch, the International Library of Childrens Literature, in the former building of the Imperial Library in Ueno. This branch contains some 400,000 items of literature from around the world. Though the NDLs original mandate was to be a library for the National Diet. In the fiscal year ending March 2004, for example, the library reported more than 250,000 reference inquiries, in contrast, as Japans national library, the NDL collects copies of all publications published in Japan. The NDL has an extensive collection of some 30 million pages of documents relating to the Occupation of Japan after World War II. This collection include the documents prepared by General Headquarters and the Supreme Commander of the Allied Powers, the Far Eastern Commission, the NDL maintains a collection of some 530,000 books and booklets and 2 million microform titles relating to the sciences
