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| {{distinguish|Inflorescence}}
| | Share trading instructors are getting to be more and more common, as the internet gives the world of [http://www.financialtrading.com/ financial trading] within the reach of the masses. If you think you know anything, you will certainly require to learn about [http://e-learning.csc.ku.ac.th/wiki/index.php?title=Obtaining_Started_into_Forex_Trading forex nitty gritty reviews]. Modern computer technology has meant that the need for [http://mondediplo.com/spip.php?page=recherche&recherche=trading+instructors trading instructors] is currently higher than ever, as people seek to get rich from the best penny stocks and take advantage of the new options. Here we"ll show you just how to go about selecting your trading and investing coach. <br><br>Tip1 <br><br>The main factor when selecting a trading coach is to look at the facts and figures. Instructors will endeavour to sell their services by declaring a certain degree of performance, and obviously you"re looking for the greatest numbers possible within reason. To learn more, we know you have a gander at: [http://poetsandquantsforexecs.com/members/rocketllama3/activity/11473/ link]. There are certainly some figures which are so high as to be unrealistic, and everyone who needs to develop his past is no good candidate for a coaching relationship. <br><br>Suggestion 2 <br><br>Be sure that a stock trading coach is strictly the thing you need. Having a coach in any endeavor can instil a feeling of control in to you that can reap great rewards. Instructors can provide an essential drive to you, and they will demand effort and application. If you think you know anything, you will maybe require to compare about [http://support.file1.com/entries/54166750-Beat-The-Forex-Marketplace-Everytime-You-Want-And-Earn-Large-Profit- Beat The Forex Marketplace Everytime You Want And Earn Large Profit! : File1.c]. As world famous billionaire investor Warren Buffett has said, Risk comes from perhaps not knowing what you are doing. If your understanding of trading is limited, a coach could be precisely what you have to help you make the big bucks in the best penny stocks. <br><br>Idea 3 <br><br>Be change careful of unrealistic prices. You have a tendency to get what you purchase in this world, and anything which seems too good to be true frequently is. Trading coaches are no exception. Why aren"t they making large sums of money with that understanding as opposed to working teaching programs for peanuts, if somebody really has exceptional capability to make judgements in the stock markets? Some people truly enjoy sharing their knowledge, but they can charge a market price for doing this. <br><br>Suggestion 4 <br><br>Do not create a long-term commitment to your trading coach before you"ve had an effort period when you can check the service. Everyone who is willing to back their sense by proving them-selves to you first is a lot more probably be a real prospect than some body who wants to get the money and work. You should probably wonder why, If a coach won"t give a trial to you. It is difficult to get the most effective small cap stocks having a coach that is no longer working out. <br><br>Stock trading coaches can turn an unprofitable investor into a highly successful one, if you can find the right one. Read the links below to discover how you can access the top penny investment tips..<br><br>If you have any inquiries regarding in which and how to use denver health ([http://royaldeity3921.sosblogs.com http://royaldeity3921.sosblogs.com]), you can make contact with us at the web-page. |
| {{Use dmy dates|date=July 2012}}
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| [[Image:Fluorescent minerals hg.jpg|thumb|right|Fluorescent minerals emit visible light when exposed to [[ultraviolet]] light]]
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| [[File:Diversity of fluorescent patterns and colors in marine fishes - journal.pone.0083259.g001.png|thumb|Fluorescent marine fishes]]
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| '''Fluorescence''' is the emission of light by a substance that has absorbed light or other [[electromagnetic radiation]].
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| It also occurs when molecules are excited to higher electronic states by energetic electron bombardment, such as occurs, for example, in the natural aurora, high-altitude nuclear explosions, and rocket-born electron gun experiments.<ref name=gilmore1992/>
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| It is a form of [[luminescence]]. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. However, when the absorbed electromagnetic radiation is intense, it is possible for one [[electron]] to absorb two [[photon]]s; this [[two-photon absorption]] can lead to emission of radiation having a shorter wavelength than the absorbed radiation. The emitted radiation may also be of the same wavelength as the absorbed radiation, termed "resonance fluorescence".<ref>''Principles Of Instrumental Analysis'' F.James Holler, Douglas A. Skoog & Stanley R. Crouch 2006</ref>
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| The most striking examples of fluorescence occur when the absorbed radiation is in the [[ultraviolet]] region of the [[spectrum]], and thus invisible to the human eye, and the emitted light is in the visible region.
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| Fluorescence has many practical applications, including [[mineralogy]], [[gemology]], chemical sensors ([[fluorescence spectroscopy]]), [[fluorescent labelling]], [[dye]]s, biological detectors, and, most commonly, [[fluorescent lamp]]s.
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| ==History==
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| [[File:Lignum nephriticum - cup of Philippine lignum nephriticum, Pterocarpus indicus, and flask containing its fluorescent solution Hi.jpg|thumb|left|upright|''[[Lignum nephriticum]]'' cup made from the wood of the narra tree (''[[Pterocarpus indicus]]''), and a flask containing its fluorescent [[Solution (chemistry)|solution]]]]
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| [[File:Matlaline -- fluorescent substance from Mexican tree, Eysenhardtia polystachya.JPG|thumb|right|Matlaline, the fluorescent substance in the wood of the tree ''Eysenhardtia polystachya'']]
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| An early observation of fluorescence was described in 1560 by [[Bernardino de Sahagún]] and in 1565 by [[Nicolás Monardes]] in the [[infusion]] known as ''[[lignum nephriticum]]'' ([[Latin]] for "kidney wood"). It was derived from the wood of two tree species, ''[[Pterocarpus indicus]]'' and ''[[Eysenhardtia polystachya]]''.<ref name="acuna">{{cite doi|10.1021/ol901022g|noedit}} Available on-line at: [http://202.127.145.151/siocl/siocl_0001/HHJdatabank/090707ol-6.pdf Chinese Academy of Science].</ref><ref name="saff">{{cite book|author= [[William Edwin Safford|Safford, William Edwin]]|title =Annual report of the Board of Regents of the Smithsonian Institution|chapter =''Lignum nephriticum''|location=Washington|publisher =Government Printing Office|year =1916|page=271–298|url =http://archive.org/download/annualreportofbo1915smitfo/annualreportofbo1915smitfo.pdf}}</ref><ref>{{Cite doi|10.1021/ed100182h|noedit}}</ref><ref>{{cite web |url=http://pubs.acs.org/doi/abs/10.1021/ed083p765 |title=The Fluorescence of Lignum nephriticum: A Flash Back to the Past and a Simple Demonstration of Natural Substance Fluorescence }}</ref> The chemical compound responsible for this fluorescence is matlaline, which is the oxidation product of one of the flavonoids found in this wood.<ref name="acuna"/>
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| In 1819, [[Edward Daniel Clarke|Edward D. Clarke]]<ref>Edward Daniel Clarke (1819) [http://books.google.com/books?id=KWc7AQAAIAAJ&pg=PA34#v=onepage&q&f=false "Account of a newly discovered variety of green fluor spar, of very uncommon beauty, and with remarkable properties of colour and phosphorescence,"] ''The Annals of Philosophy'', '''14''' : 34 - 36; from page 35: "The finer crystals are perfectly transparent. Their colour by transmitted light is an intense ''emerald green''; but by reflected light, the colour is a deep ''sapphire blue''; … ".</ref> and in 1822 [[René Just Haüy]]<ref>Haüy merely repeats Clarke's observation regarding the colors of the specimen of fluorite which he (Clarke) had examined: Haüy, ''Traité de Minéralogie'', 2nd ed. (Paris, France: Bachelier and Huzard, 1822), vol. 1, page 512. Fluorite is called "chaux fluatée" by Haüy. [http://books.google.com/books?id=MvcTAAAAQAAJ&pg=PA512#v=onepage&q&f=false From page 512]: "... violette par réflection, et verdâtre par transparence au Derbyshire." ([the color of fluorite is] violet by reflection, and greenish by transmission in [specimens from] Derbyshire.)</ref> described fluorescence in [[fluorite]]s, [[Sir David Brewster]] described the phenomenon for [[chlorophyll]] in 1833<ref>David Brewster (1834) [http://books.google.com/books?id=I_UQAAAAIAAJ&pg=PA538#v=onepage&q&f=false "On the colours of natural bodies,"] ''Transactions of the Royal Society of Edinburgh'' '''12''' : 538-545; on page 542, Brewster mentions that when white light passes through an alcoholic solution of chlorophyll, red light is reflected from it.</ref> and [[Sir John Herschel]] did the same for [[quinine]] in 1845.<ref>See:
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| * Herschel, John (1845a) [http://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA143#v=onepage&q&f=false "On a case of superficial colour presented by a homogeneous liquid internally colourless,"] ''Philosophical Transactions of the Royal Society of London'', '''135''' : 143-145; see page 145.
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| * Herschel, John (1845b) [http://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA147#v=onepage&q&f=false "On the epipŏlic dispersion of light, being a supplement to a paper entitled, "On a case of superficial colour presented by a homogeneous liquid internally colourless" ,"] ''Philosophical Transactions of the Royal Society of London'', '''135''' : 147-153.</ref>
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| In his 1852 paper on the "Refrangibility" ([[wavelength]] change) of light, [[George Gabriel Stokes]] described the ability of [[fluorite|fluorspar]] and [[uranium glass]] to change invisible light beyond the violet end of the visible spectrum into blue light. He named this phenomenon ''fluorescence'' : "I am almost inclined to coin a word, and call the appearance ''fluorescence'', from fluor-spar [i.e., fluorite], as the analogous term ''opalescence'' is derived from the name of a mineral."<ref>{{cite journal
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| |title=On the Change of Refrangibility of Light
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| |author=Stokes, G. G.
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| |year=1852
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| |journal=Philosophical Transactions of the Royal Society of London |volume=142 |pages=463–562
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| |url=http://books.google.com/books?id=CE9FAAAAcAAJ&pg=PA463#v=onepage&q&f=false
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| |doi=10.1098/rstl.1852.0022 }} From page 479, footnote: "I am almost inclined to coin a word, and call the appearance ''fluorescence'', from fluor-spar, as the analogous term ''opalescence'' is derived from the name of a mineral."</ref> The name was derived from the mineral [[fluorite]] (calcium difluoride), some examples of which contain traces of divalent [[europium]], which serves as the fluorescent activator to emit blue light. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight and observed blue light emitted by an ethanol solution of quinine exposed by it.<ref>Stokes (1852), pages 472-473. In a footnote on page 473, Stokes acknowledges that in 1843, [[A. E. Becquerel|Edmond Becquerel]] had observed that quinine acid sulfate strongly absorbs ultraviolet radiation (i.e., solar radiation beyond Fraunhofer's H band in the solar spectrum). See: Edmond Becquerel (1843) [http://gallica.bnf.fr/ark:/12148/bpt6k2976b/f894.image "Des effets produits sur les corps par les rayons solaires"] (On the effects produced on substances by solar rays), ''Comptes rendus'', '''17''' : 882-884; on page 883, Becquerel cites quinine acid sulfate ("sulfate acide de quinine") as strongly absorbing ultraviolet light.</ref>
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| ==Physical principles==
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| ===Photochemistry===
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| Fluorescence occurs when an orbital [[electron]] of a molecule, atom or [[nanostructure]] relaxes to its [[ground state]] by emitting a [[photon]] of light after being [[excited state|excited]] to a higher quantum state by some type of energy:<ref name="mehta" />
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| Excitation: <math> S_0 + h \nu_{ex} \to S_1 </math>
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| Fluorescence (emission): <math> S_1 \to S_0 + h \nu_{em} + heat </math>
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| here <math> h\nu </math> is a generic term for photon energy with h = [[Planck's constant]] and <math>\nu</math> = [[frequency]] of light. (The specific frequencies of exciting and emitted light are dependent on the particular system.)
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| State S<sub>0</sub> is called the ground state of the [[fluorophore]] (fluorescent molecule) and S<sub>1</sub> is its first (electronically) excited state.
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| A molecule, S<sub>1</sub>, can relax by various competing pathways. It can undergo 'non-radiative relaxation' in which the excitation energy is dissipated as [[heat]] (vibrations) to the solvent. Excited organic molecules can also relax via conversion to a [[triplet state]], which may subsequently relax via [[phosphorescence]] or by a secondary non-radiative relaxation step.
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| Relaxation of an S<sub>1</sub> state can also occur through interaction with a second molecule through [[Quenching (fluorescence)|fluorescence quenching]]. Molecular [[oxygen]] (O<sub>2</sub>) is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state.
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| Molecules that are excited through light absorption or via a different process (e.g. as the product of a reaction) can transfer energy to a second 'sensitized' molecule, which is converted to its excited state and can then fluoresce. This process is used in [[lightstick]]s to produce different colors.
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| ===Quantum yield===
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| 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.<ref>Lakowicz, Joseph R. Principles of Fluorescence Spectroscopy(second edition). Kluwer Academic / Plenum Publishers, 1999 p. 10</ref><ref>Valeur, Bernard, Berberan-Santos, Mario 2012. ''Molecular Fluorescence: Principles and Applications'' 2nd ed., Wiley-VCH, p. 64</ref>
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| : <math> \Phi = \frac {\textrm{Number of photons emitted}} {\textrm{Number of photons absorbed}} </math>
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| The maximum fluorescence quantum yield is 1.0 (100%); every [[photon]] absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent. Another way to define the quantum yield of fluorescence, is by the rate of excited state decay:
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| : <math> \Phi = \frac{ { k}_{ f} }{ \sum_{i}{ k}_{i } } </math>
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| where <math>{ k}_{ f}</math> is the rate of [[spontaneous emission]] of radiation and
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| :<math> \sum_{i}{ k}_{i } </math>
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| is the sum of all rates of excited state decay. Other rates of excited state decay are caused by mechanisms other than photon emission and are, therefore, often called "non-radiative rates", which can include:
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| dynamic collisional quenching, near-field dipole-dipole interaction (or [[resonance energy transfer]]), internal conversion, and [[intersystem crossing]]. Thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected.
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| 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.
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| ===Lifetime===
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| [[File:Jablonski Diagram of Fluorescence Only.png|thumb|Jablonski diagram. After an electron absorbs a high energy photon the system is excited electronically and vibrationally. The system relaxes vibrationally, and eventually fluoresces at a longer wavelength.]]
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| The fluorescence lifetime refers to the average time the molecule stays in its excited state before emitting a photon. Fluorescence typically follows [[first-order kinetics]]:
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| :<math> \left[S 1 \right] = \left[S 1 \right]_0 e^{-\Gamma t} </math>
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| where <math>\left[S 1 \right]</math> is the concentration of excited state molecules at time <math>t</math>, <math>\left[S 1 \right]_0</math> is the initial concentration and [[Gamma|<math>\Gamma</math>]] is the decay rate or the inverse of the fluorescence lifetime. This is an instance of [[exponential decay]]. Various radiative and non-radiative processes can de-populate the excited state. In such case the total decay rate is the sum over all rates:
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| :<math> \Gamma_{tot}=\Gamma_{rad} + \Gamma_{nrad} </math>
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| where <math>\Gamma_{tot}</math> is the total decay rate, <math>\Gamma_{rad}</math> the radiative decay rate and <math>\Gamma_{nrad}</math> the non-radiative decay rate. It is similar to a first-order chemical reaction in which the first-order rate constant is the sum of all of the rates (a parallel kinetic model). If the rate of spontaneous emission, or any of the other rates are fast, the lifetime is short. For commonly used fluorescent compounds, typical excited state decay times for photon emissions with energies from the [[Ultraviolet|UV]] to [[near infrared]] are within the range of 0.5 to 20 [[nanoseconds]]. The fluorescence lifetime is an important parameter for practical applications of fluorescence such as [[fluorescence resonance energy transfer]] and [[Fluorescence-lifetime imaging microscopy]].
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| ===Jablonski diagram===
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| The [[Jablonski diagram]] describes most of the relaxation mechanisms for excited state molecules. The diagram alongside shows how fluorescence occurs due to the relaxation of certain excited electrons of a molecule.<ref name="mehta">[http://pharmaxchange.info/press/2013/03/animation-for-the-principle-of-fluorescence-and-uv-visible-absorbance/ Animation for the principle of fluorescence and UV-visible absorbance]</ref>
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| ===Fluorescence anisotropy===
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| Fluorophores are more likely to be excited by photons if the transition moment of the fluorophore is parallel to the electric vector of the photon.<ref>Lakowicz, J. R. (1999). Principles of Fluorescence Spectroscopy. Kluwer Academic / Plenum Publishers pp 12-13</ref> The polarization of the emitted light will also depend on the transition moment. The transition moment is dependent on the physical orientation of the fluorophore molecule. For fluorophores in solution this means that the intensity and polarization of the emitted light is dependent on rotational diffusion. Therefore, anisotropy measurements can be used to investigate how freely a fluorescent molecule moves in a particular environment.
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| Fluorescence anisotropy can be defined quantitatively as
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| :<math>r = {I_\parallel - I_\perp \over I_\parallel + 2I_\perp}</math>
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| where <math>I_\parallel</math> is the emitted intensity parallel to polarization of the excitation light and <math>I_\perp</math> is the emitted intensity perpendicular to the polarization of the excitation light.<ref>Valeur, Bernard, Berberan-Santos, Mario 2012. ''Molecular Fluorescence: Principles and Applications'' 2nd ed., Wiley-VCH, p.186</ref>
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| ==Rules==
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| There are several general [[rule of thumb|rules]] that deal with fluorescence. Each of the following rules has exceptions but they are useful guidelines for understanding fluorescence. (These rules do not necessarily apply to [[Two-photon absorption]].)
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| ===Kasha–Vavilov rule===
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| The [[Kasha's rule|Kasha–Vavilov rule]] dictates that the quantum yield of luminescence is independent of the wavelength of exciting radiation.<ref>[[International Union of Pure and Applied Chemistry|IUPAC]]. [http://goldbook.iupac.org/K03371.html Kasha–Vavilov rule – Compendium of Chemical Terminology, 2nd ed. (the "Gold Book")]. Compiled by McNaught, A.D. and Wilkinson, A. Blackwell Scientific Publications, Oxford, 1997.</ref> This occurs because excited molecules usually decay to the lowest vibrational level of the excited state before fluorescence emission takes place. The Kasha–Vavilov rule does not always apply and is violated severely in many simple molecules. A somewhat more reliable statement, although still with exceptions, would be that the fluorescence spectrum shows very little dependence on the wavelength of exciting radiation.{{citation needed|date=August 2011}}
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| ===Mirror image rule===
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| For many fluorophores the absorption spectrum is a mirror image of the emission spectrum.<ref>Lakowicz, J. R. (1999). Principles of Fluorescence Spectroscopy. Kluwer Academic / Plenum Publishers pp 6–8</ref> This is known as the mirror image rule and is related to the [[Franck–Condon principle]] which states that electronic transitions are vertical, that is energy changes without distance changing as can be represented with a vertical line in Jablonski diagram. This means the nucleus does not move and the vibration levels of the excited state resemble the vibration levels of the ground state.
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| ===Stokes shift===
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| In general, emitted fluorescent light has a longer wavelength and lower energy than the absorbed light.<ref>Lakowicz, J. R. (1999). Principles of Fluorescence Spectroscopy. Kluwer Academic / Plenum Publishers pp 6–7</ref> This phenomenon, known as [[Stokes shift]], is due to energy loss between the time a photon is absorbed and when it is emitted. The causes and magnitude of Stokes shift can be complex and are dependent on the fluorophore and its environment. However, there are some common causes. It is frequently due to non-radiative decay to the lowest vibrational energy level of the excited state. Another factor is that the emission of fluorescence frequently leaves a fluorophore in the highest vibrational level of the ground state.
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| ==Fluorescence in nature==
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| There are many natural compounds that exhibit fluorescence, and they have a number of applications. Some deep-sea animals, such as the [[greeneye]], use fluorescence.
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| ===Gemology, mineralogy, and geology===
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| [[File:Aragonit_-_Fluorescence.gif|thumb|left|Fluorescence of Aragonite]]
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| [[Gemstone]]s, [[mineral]]s, may have a distinctive fluorescence or may fluoresce differently under short-wave ultraviolet, long-wave ultraviolet, or [[X-ray]]s.
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| Many types of [[calcite]] and amber will fluoresce under shortwave UV. [[Ruby|Rubies]], [[emerald]]s, and the [[Hope Diamond]] exhibit red fluorescence under short-wave UV light; diamonds also emit light under [[X-ray]] radiation.
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| Fluorescence in minerals is caused by a wide range of activators. In some cases, the concentration of the activator must be restricted to below a certain level, to prevent quenching of the fluorescent emission. Furthermore, certain impurities such as iron or copper need to be absent, to prevent quenching of possible fluorescence. Divalent [[manganese]], in concentrations of up to several percent, is responsible for the red or orange fluorescence of [[calcite]], the green fluorescence of [[willemite]], the yellow fluorescence of [[esperite]], and the orange fluorescence of [[wollastonite]] and [[clinohedrite]]. Hexavalent [[uranium]], in the form of the [[uranyl cation]], fluoresces at all concentrations in a yellow green, and is the cause of fluorescence of minerals such as [[autunite]] or [[andersonite]], and, at low concentration, is the cause of the fluorescence of such materials as some samples of [[hyalite opal]]. Trivalent [[chromium]] at low concentration is the source of the red fluorescence of [[ruby]]. Divalent [[europium]] is the source of the blue fluorescence, when seen in the mineral [[fluorite]]. Trivalent [[lanthanide]]s such as [[terbium]] and [[dysprosium]] are the principal activators of the creamy yellow fluorescence exhibited by the [[yttrofluorite]] variety of the mineral fluorite, and contribute to the orange fluorescence of [[zircon]]. [[Powellite]] ([[calcium molybdate]]) and [[scheelite]] (calcium tungstate) fluoresce intrinsically in yellow and blue, respectively. When present together in solid solution, energy is transferred from the higher-energy [[tungsten]] to the lower-energy [[molybdenum]], such that fairly low levels of [[molybdenum]] are sufficient to cause a yellow emission for [[scheelite]], instead of blue. Low-iron [[sphalerite]] (zinc sulfide), fluoresces and phosphoresces in a range of colors, influenced by the presence of various trace impurities.
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| Crude oil ([[petroleum]]) fluoresces in a range of colors, from dull-brown for heavy oils and tars through to bright-yellowish and bluish-white for very light oils and condensates. This phenomenon is used in [[oil exploration]] drilling to identify very small amounts of oil in drill cuttings and core samples.
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| ===Organic liquids===
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| Organic solutions such [[anthracene]] or [[stilbene]], dissolved in [[benzene]] or [[toluene]], fluoresce with [[ultraviolet]] or [[gamma ray]] [[irradiation]]. The decay times of this fluorescence are of the order of nanoseconds, since the duration of the light depends on the lifetime of the excited states of the fluorescent material, in this case anthracene or stilbene.{{Citation needed|date=March 2011}}
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| ===Common materials that fluoresce===
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| * [[Vitamin B2]] fluoresces yellow.
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| * [[Tonic water]] fluoresces blue due to the presence of [[quinine]].
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| * [[Highlighter]] ink is often fluorescent due to the presence of [[pyranine]].
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| * [[Banknote]]s, [[postage stamp]]s and [[credit card]]s often have fluorescent security features.
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| ==Applications of fluorescence==
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| ===Lighting===
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| {{details|Fluorescent lamp}}
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| [[Image:Www Beo cc.jpg|thumb|Fluorescent paint and plastic lit by [[UV tube]]s. Paintings by Beo Beyond]]
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| The common [[fluorescent lamp]] relies on fluorescence. Inside the [[glass]] tube is a partial vacuum and a small amount of [[mercury (element)|mercury]]. An electric discharge in the tube causes the mercury atoms to emit ultraviolet light. The tube is lined with a coating of a fluorescent material, called the ''[[phosphor]]'', which absorbs the ultraviolet and re-emits visible light. Fluorescent [[lighting]] is more energy-efficient than [[incandescent]] lighting elements. However, the uneven [[spectrum]] of traditional fluorescent lamps may cause certain colors to appear different than when illuminated by incandescent light or [[daylight]]. The mercury vapor emission spectrum is dominated by a short-wave UV line at 254 nm (which provides most of the energy to the phosphors), accompanied by visible light emission at 436 nm (blue), 546 nm (green) and 579 nm (yellow-orange). These three lines can be observed superimposed on the white continuum using a hand spectroscope, for light emitted by the usual white fluorescent tubes. These same visible lines, accompanied by the emission lines of trivalent europium and trivalent terbium, and further accompanied by the emission continuum of divalent europium in the blue region, comprise the more discontinuous light emission of the modern trichromatic phosphor systems used in many [[compact fluorescent lamp]] and traditional lamps where better color rendition is a goal.<ref name="How Fluorescent Lamps Work">{{cite web|last=Harris|first=Tom|title=How Fluorescent Lamps Work|url=http://home.howstuffworks.com/fluorescent-lamp.htm|work=HowStuffWorks|publisher=Discovery Communications|accessdate=27 June 2010}}</ref>
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| Fluorescent lights were first available to the public at the [[1939 New York World's Fair]]. Improvements since then have largely been better phosphors, longer life, and more consistent internal discharge, and easier-to-use shapes (such as compact fluorescent lamps). Some [[Gas-discharge lamp#High-intensity discharge lamps|high-intensity discharge (HID) lamps]] couple their even-greater electrical efficiency with phosphor enhancement for better color rendition.{{Citation needed|date=July 2010}}
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| White [[light-emitting diode]]s (LEDs) became available in the mid-1990s as [[LED lamp]]s, in which blue light emitted from the [[semiconductor]] strikes phosphors deposited on the tiny chip. The combination of the blue light that continues through the phosphor and the green to red fluorescence from the phosphors produces a net emission of white light.{{Citation needed|date=July 2010}}
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| [[Glow stick]]s sometimes utilize fluorescent materials to absorb light from the [[chemiluminescence|chemiluminescent]] reaction and emit light of a different color.<ref name="How Fluorescent Lamps Work"/>
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| ===Analytical chemistry===
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| Many analytical procedures involve the use of a [[fluorometer]], usually with a single exciting wavelength and single detection wavelength. Because of the sensitivity that the method affords, fluorescent molecule concentrations as low as 1 part per trillion can be measured.<ref>"Fluorometric Assay Using Dimeric Dyes for Double- and Single-Stranded DNA and RNA with Picogram Sensitivity"; H.S. Rye, J.M. Dabora, M.A. Quesada, R.A. Mathies, A.N. Glazer, Analytical Biochemistry, Volume 208, Issue 1, January 1993, Pages 144–150, http://dx.doi.org/10.1006/abio.1993.1020</ref>
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| Fluorescence in several wavelengths can be detected by an [[Chromatography detector|array detector]], to detect compounds from [[High-performance liquid chromatography|HPLC]] flow. Also, [[Thin layer chromatography|TLC]] plates can be visualized if the compounds or a coloring reagent is fluorescent. Fluorescence is most effective when there is a larger ratio of atoms at lower energy levels in a [[Boltzmann distribution]]. There is, then, a higher probability of excitement and release of photons by lower-energy atoms, making analysis more efficient.
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| ===Spectroscopy===
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| {{Main|Fluorescence spectroscopy}}
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| Usually the setup of a fluorescence assay involves a light source, which may emit many different wavelengths of light. In general, a single wavelength is required for proper analysis, so, in order to selectively filter the light, it is passed through an excitation monochromator, and then that chosen wavelength is passed through the sample cell. After absorption and re-emission of the energy, many wavelengths may emerge due to [[Stokes shift]] and various [[electron transition]]s. To separate and analyze them, the fluorescent radiation is passed through an emission [[monochromator]], and observed selectively by a detector.<ref>{{cite book|author=Daniel C. Harris|title=Exploring chemical analysis|url=http://books.google.com/books?id=x5eEW76lizEC|accessdate=16 April 2011|date=May 2004|publisher=Macmillan|isbn=978-0-7167-0571-0}}</ref>
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| ===Biochemistry and medicine===
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| {{Main|Fluorescence in the life sciences}}
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| [[Image:FluorescentCells.jpg|thumb|right|[[Endothelium|Endothelial cells]] under the microscope with three separate channels marking specific cellular components]]
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| Fluorescence in the life sciences is used generally as a non-destructive way of tracking or analysis of biological molecules by means of the fluorescent emission at a specific frequency where there is no background from the excitation light, as relatively few cellular components are naturally fluorescent (called intrinsic or [[autofluorescence]]).
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| In fact, a [[protein]] or other component can be "labelled" with an extrinsic [[fluorophore]], a fluorescent [[dye]] that can be a small molecule, protein, or quantum dot, finding a large use in many biological applications.<ref>{{cite book|author=Joseph R. Lakowicz|title=Principles of fluorescence spectroscopy|url=http://books.google.com/books?id=-PSybuLNxcAC|accessdate=16 April 2011|year=2006|publisher=Springer|isbn=978-0-387-31278-1|page=xxvi}}</ref>
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| The quantification of a dye is done with a [[spectrofluorometer]] and finds additional applications in:
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| ====Microscopy====
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| * When scanning the fluorescent intensity across a plane one has [[fluorescence microscope|fluorescence microscopy]] of tissues, cells, or subcellular structures, which is accomplished by labeling an antibody with a fluorophore and allowing the antibody to find its target antigen within the sample. Labelling multiple antibodies with different fluorophores allows visualization of multiple targets within a single image (multiple channels). DNA microarrays are a variant of this.
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| * Immunology: An antibody is first prepared by having a fluorescent chemical group attached, and the sites (e.g., on a microscopic specimen) where the antibody has bound can be seen, and even quantified, by the fluorescence.
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| * FLIM ([[Fluorescence Lifetime Imaging Microscopy]]) can be used to detect certain bio-molecular interactions that manifest themselves by influencing fluorescence lifetimes.
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| * Cell and molecular biology: detection of [[colocalization]] using fluorescence-labelled antibodies for selective detection of the antigens of interest using specialized software, such as [[CoLocalizer Pro]].
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| ====Other techniques====
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| * FRET ([[Fluorescence resonance energy transfer]] or [[Förster resonance energy transfer]]) is used to study protein interactions, detect specific nucleic acid sequences and used as biosensors, while fluorescence lifetime (FLIM) can give an additional layer of information.
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| * Biotechnology: [[biosensors]] using fluorescence are being studied as possible [[Fluorescent glucose biosensors]].
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| * Automated sequencing of [[DNA]] by the [[chain termination method]]; each of four different chain terminating bases has its own specific fluorescent tag. As the labelled DNA molecules are separated, the fluorescent label is excited by a UV source, and the identity of the base terminating the molecule is identified by the wavelength of the emitted light.
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| * FACS ([[fluorescence-activated cell sorting]]). One of several important [[cell sorting]] techniques used in the separation of different cell lines (especially those isolated from animal tissues).
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| * DNA detection: the compound [[ethidium bromide]], in aqueous solution, has very little fluorescence, as it is quenched by water. Ethidium bromide's fluorescence is greatly enhanced after it binds to DNA, so this compound is very useful in visualising the location of DNA fragments in [[agarose gel electrophoresis]]. Intercalated ethidium is in a hydrophobic environment when it is between the base pairs of the DNA, protected from quenching by water which is excluded from the local environment of the intercalated ethidium. Ethidium bromide may be carcinogenic – an arguably safer alternative is the dye [[SYBR Green]].
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| * FIGS ([[Fluorescence image-guided surgery]]) is a medical imaging technique that uses fluorescence to detect properly labeled structures during surgery.
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| * SAFI (species altered fluorescence imaging) an imaging technique in [[electrokinetic phenomena|electrokinetics]] and [[microfluidics]].<ref>https://microfluidics.stanford.edu/Publications/ParticleTracking_Diagnostics/Shkolnikov_A%20method%20for%20non-invasive%20full-field%20imaging%20and%20quantification%20of%20chemical%20species.pdf</ref> It uses non-electromigrating dyes whose fluorescence is easily quenched by migrating chemical species of interest. The dye(s) are usually seeded everywhere in the flow and differential quenching of their fluorescence by analytes is directly observed.
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| ===Forensics===
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| [[Fingerprint]]s can be visualized with fluorescent compounds such as [[ninhydrin]]. Blood and other substances are sometimes detected by fluorescent reagents, like [[fluorescein]]. [[Fiber]]s, and other materials that may be encountered in [[Forensic science|forensics]] or with a relationship to various [[collectible]]s, are sometimes fluorescent.
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| ==See also==
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| {{colbegin|3}}
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| * Absorption-re-emission [[atomic line filter]]s use the phenomenon of fluorescence to filter light extremely effectively.
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| * [[Black light]]
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| * [[Blacklight paint]]
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| * [[Evos microscope]]
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| * [[Fluorescence correlation spectroscopy]]
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| * [[Fluorescence image-guided surgery]]
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| * [[Fluorescence in plants]]
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| * [[Fluorescence spectroscopy]]
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| * [[Fluorescent lamp]]
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| * [[Fluorescent multilayer card]]
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| * [[Fluorescent Multilayer Disc]]
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| * [[Fluorometer]]
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| * [[High-visibility clothing]]
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| * [[Laser-induced fluorescence]]
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| * [[List of light sources]]
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| * [[Mössbauer effect]], resonant fluorescence of gamma rays
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| * [[Organic light-emitting diode]]s can be fluorescent
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| * [[Phosphorescence]]
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| * [[Phosphor thermometry]], the use of phosphorescence to measure temperature.
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| * [[Spectroscopy]]
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| * [[Two-photon absorption]]
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| * [[Vibronic spectroscopy]]
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| * [[X-ray fluorescence]]
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| {{colend}}
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| ==References==
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| {{reflist|30em
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| <ref name=gilmore1992>
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| {{cite journal
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| | last = Gilmore
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| | first = Forrest R.
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| | display-authors = 1
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| | last2 = Laher
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| | first2 = Russ R.
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| | last3 = Espy
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| | first3 = Patrick J.
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| | year = 1992
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| | title = Franck-Condon Factors, r-Centroids, Electronic Transition Moments, and Einstein Coefficients for Many Nitrogen and Oxygen Band Systems
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| | journal = [[Journal of Physical and Chemical Reference Data]]
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| | volume = 21
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| | issue = 5
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| | pages = 1005-1107
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| }}
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| </ref>
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| }}
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| ==External links==
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| {{commons category|Fluorescence}}
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| * [http://www.fluorophores.org Fluorophores.org], the database of fluorescent dyes
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| * [http://micro.magnet.fsu.edu/primer/techniques/fluorescence/fluorescenceintro.html FSU.edu], Basic Concepts in Fluorescence
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| * [http://www.lfd.uci.edu/workshop/2008/ "A nano-history of fluorescence" lecture by David Jameson]
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| * [http://www.mcb.arizona.edu/IPC/spectra_page.htm Excitation and emission spectra of various fluorescent dyes]
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| * [http://www.fluomin.org/uk/list.php Database of fluorescent minerals with pictures, activators and spectra (fluomin.org)]
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| {{Artificial light sources}}
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| [[Category:Fluorescence| ]]
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| [[Category:Dyes]]
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| [[Category:Molecular biology]]
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| [[Category:Radiochemistry]]
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