Fluorescence 11555 223069842 2008-07-02T12:42:57Z MER-C 1749459 Reverted edits by [[Special:Contributions/24.98.24.188|24.98.24.188]] ([[User talk:24.98.24.188|talk]]) to last version by Untionic {{Unreferenced|date=September 2007}} [[Image:Fluorescent minerals hg.jpg|thumb|300px|right|Fluorescent minerals]] '''Fluorescence''' is a [[luminescence]] that<!--"which" is some what incorrect, for a distinction is to be made in the various types of luminescence--> is mostly found as an [[optical phenomenon]] in cold bodies, in which the molecular absorption of a [[photon]] triggers the emission of another photon with a longer [[wavelength]]. The energy difference between the absorbed and emitted photons ends up as molecular [[kinetic energy|vibrations]] or [[heat]]. Usually the absorbed photon is in the [[ultraviolet]] range, and the emitted [[light]] is in the visible range, but this depends on the absorbance curve and [[Stokes shift]] of the particular [[fluorophore]]. Fluorescence was coined by [[George Gabriel Stokes]] in his 1852 paper, the name was given as a description of the essence of the [[mineral]] [[fluorite]], composed of [[calcium fluoride]], which gave a visible emission when illuminated with "invisible radiation" [[UV]] radiation. ==Equations== ===Photochemistry=== Fluorescence occurs when a molecule , atom or [[nanostructure]] relaxes to its [[ground state]] after being electrically excited. Excitation: <math> S_0 + h \nu \to S_1 </math> Fluorescence (emission): <math>S_1 \to S_0 + h \nu</math>, here <math>h \nu</math> is a generic term for photon energy where: 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.) 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. A molecule in its excited state, 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. 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 because of its unusual triplet ground state. 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. ===Quantum yield=== 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. : <math> \Phi = \frac {\rm \#\ photons \ emitted} {\rm \#\ photons \ absorbed} </math> 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 rates excited state decay: : <math> \frac{ { k}_{ f} }{ \sum_{i}{ k}_{i } } </math> where <math>{ k}_{ f}</math> is the rate of [[spontaneous emission]] of radiation and : <math> \sum_{i}{ k}_{i } </math> 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: 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, this will affect both the excited state lifetime and the fluorescence quantum yield. Fluorescence quantum yield are measured by comparison to a standard with known quantology; the [[quinine]] salt, quinine sulfate, in a sulfuric acid solution is a common fluorescence standard. ===Lifetime=== 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: :<math> \left[S 1 \right] = \left[S 1 \right]_0 e^{-\Gamma t}, </math> 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 <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: :<math> \Gamma_{tot}=\Gamma_{rad} + \Gamma_{nrad} </math> 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 fluorescent compounds that emit photons with energies from the [[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]]. ==Rules== There are several [[rule of thumb|rules]] that deal with fluorescence. The [[Kasha–Vavilov rule]] dictates that the quantum yield of luminescence is independent of the wavelength of exciting radiation. This is not always true 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. The ''[[Jablonski diagram]]'' describes most of the relaxation mechanism for excited state molecules. ==Applications== There are many natural and synthetic compounds that exhibit fluorescence, and they have a number of applications. Some deep-sea animals, such as the [[Greeneye]], use fluorescence. ===Lighting=== The common [[fluorescent lamp|fluorescent tube]] 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 light. The emitted light is in the [[ultraviolet]] (UV) range, is invisible, and is harmful to most living organisms. 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 very energy efficient compared to [[incandescent]] technology, but the [[Visible spectrum|spectra]] produced may cause certain colours to appear unnatural. In the mid 1990s, white [[light-emitting diode]]s (LEDs) became available, which work through a similar process. Typically, the actual light-emitting [[semiconductor]] produces light in the blue part of the spectrum, which strikes a phosphor compound deposited on the chip; the phosphor fluoresces from the green to red part of the spectrum. The combination of the blue light that goes through the phosphor and the light emitted by the phosphor produce a net emission of white light. The modern [[mercury vapor]] [[streetlight]] is said to have been evolved from the fluorescent lamp. [[Lightstick|Glow sticks]] oxidise [[phenyl oxalate ester]] in order to produce light. [[Compact fluorescent lamp|Compact fluorescent lighting]] (CFL) is the same as any typical fluorescent lamp with advantages. It is self-ballasted and used to replace incandescents in most applications. They produce a quarter of the heat per lumen as [[incandescent]] bulbs and last about five times as long. These bulbs contain mercury and must be handled and disposed with care. The disadvantages to the self-ballasting properties of compact fluorescent is that they may not fit properly in all light fixtures. All fluorescent lights have a significant delay in turning on compared to incandescents, a disadvantage in some applications. Additionally, the technology which allows them to be 'plug-and-play' also significantly reduces their life-span and reliability in dimming applications. ===Analytical chemistry=== Fluorescence in several wavelengths can be detected by an [[array detector]], to detect compounds from [[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 levels in a [[Boltzmann distribution]] because then there is more of a chance those atoms will be excited then release a photon and can be analyzed. [[Fingerprint]]s can be visualized with fluorescent compounds such as [[ninhydrin]]. ==Biochemistry and medicine== Biological molecules can be tagged with a fluorescent chemical group ([[fluorophore]]) by a simple chemical reaction, and the fluorescence of the tag enables sensitive and quantitative detection of the molecule. Examples: * [[fluorescence microscope|Fluorescence microscopy]] of tissues, cells or subcellular structures is accomplished by labeling an antibody with a fluorophore and allowing the antibody to find its target antigen within the sample. Labeling multiple antibodies with different fluorophores allows visualization of multiple targets within a single image. * Automated sequencing of [[DNA]] by the [[chain termination method]]; each of four different chain terminating bases has its own specific fluorescent tag. As the labeled 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. [[Image:AgarosegelUV.jpg|thumb|right|Ethidium bromide stained [[agarose gel electrophoresis|agarose gel]]. Ethidium bromide [[fluorescence|fluoresces]] orange when [[intercalation (chemistry)|intercalating]] [[DNA]] and when exposed to [[UV]] light.]] * DNA detection: the compound [[ethidium bromide]], when free to change its conformation in solution, has very little fluorescence. Ethidium bromide's fluorescence is greatly enhanced when it binds to DNA, so this compound is very useful in visualising the location of DNA fragments in [[agarose gel electrophoresis]]. Ethidium bromide can be toxic - a safer alternative is the dye [[SYBR Green]]. * The [[DNA microarray]] * Immunology: An antibody has 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. * FACS ([[fluorescent-activated cell sorting]]) * Fluorescence has been used to study the structure and conformations of DNA and proteins with techniques such as [[Fluorescence resonance energy transfer]], which measures distance at the angstrom level. This is especially important in complexes of multiple biomolecules. * [[Aequorin]], from the jellyfish ''[[Aequorea victoria]]'', produces a blue glow in the presence of Ca<sup>2+</sup> ions (by a chemical reaction). It has been used to image calcium flow in cells in real time. The success with aequorin spurred further investigation of ''A. victoria'' and led to the discovery of [[Green Fluorescent Protein]] (GFP), which has become an extremely important research tool. GFP and related proteins are used as reporters for any number of biological events including such things as sub-cellular localization. Levels of gene expression are sometimes measured by linking a gene for GFP production to another gene. Also, many biological molecules have an intrinsic fluorescence that can sometimes be used without the need to attach a chemical tag. Sometimes this intrinsic fluorescence changes when the molecule is in a specific environment, so the distribution or binding of the molecule can be measured. [[Bilirubin]], for instance, is highly fluorescent when bound to a specific site on serum albumin. [[Zinc protoporphyrin]], formed in developing red blood cells instead of hemoglobin when iron is unavailable or lead is present, has a bright fluorescence and can be used to detect these problems. As of 2006, the number of fluorescence applications is growing in the biomedical biological and related sciences. Methods of analysis in these fields are also growing, albeit with increasingly unfortunate nomenclature in the form of acronyms such as: [[Fluorescence lifetime imaging|FLIM]], FLI, [[Fluorescence loss in photobleaching|FLIP]], CALI, FLIE, [[Fluorescence resonance energy transfer|FRET]], [[Fluorescence recovery after photobleaching|FRAP]], [[Fluorescence correlation spectroscopy|FCS]], PFRAP, smFRET, FIONA, FRIPS, SHREK, SHRIMP, TIRF. Most of these techniques rely on fluorescence microscopes. These microscopes use high intensity light sources, usually mercury or xenon lamps, LEDs, or lasers, to excite fluorescence in the samples under observation. Optical filters then separate excitation light from emitted fluorescence, to be detected by eye, or with a (CCD) camera or other light detectors (photomultiplier tubes, spectrographs, etc). Much research is underway to improve the capabilities of such microscopes, the fluorescent probes used, and the applications they are applied to. Of particular note are confocal microscopes, which use a pinhole to achieve optical sectioning – affording a quantitative, 3D view of the sample. ==Gemology, mineralogy, geology, and forensics== [[Gemstone]]s, [[mineral]]s, [[fiber]]s, and many other materials which may be encountered in [[Forensic science|forensics]] or with a relationship to various [[collectible]]s may have a distinctive fluorescence or may fluoresce differently under short-wave ultraviolet, long-wave ultra violet, or [[X-ray]]s. Many types of [[calcite]] and [http://www.ambarazul.com/newsletter/april06 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. 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 sample. ==Organic liquids== Organic liquids such as mixtures of [[anthracene]] in [[benzene]] or [[toluene]], or [[stilbene]] in the same [[solvent]]s, fluoresce with [[ultraviolet]] or [[gamma ray]] [[irradiation]]. The decay times of this fluorescence is 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. ==See also== * Absorption-re-emission [[atomic line filter]]s use the phenomenon of fluorescence to filter light extremely effectively. * [[Black light]] * [[Blacklight paint]] * [[Fluorescence correlation spectroscopy]] * [[Fluorescence in plants: natural and modified]] * [[Fluorescence spectroscopy]] * [[Fluorescent multilayer card]] * [[Fluorescent Multilayer Disc]] * [[Fluorescent lamp]] * [[Fluorometer]] * [[High-visibility clothing]] * [[Laser-induced fluorescence]] * [[List of light sources]] * [[Phosphorescence]] * [[X-ray fluorescence]] ==References== <references/> {{Unreferenced|date=April 2008}} ==External links== {{commonscat|Fluorescence}} * [http://www.pti-nj.com/Applications.html Fluorescence Applications] Spanning the UV, Vis, and NIR by Photon Technology International Inc. * [http://jobinyvon.com/SiteResources/Data/Templates/1divisional.asp?DocID=514&v1ID=&lang=] Fluorescence Applications & Instruments Slideshows | HORIBA Jobin Yvon * [https://www.micro-shop.zeiss.com/?s=2525647761b33&l=en&p=us&f=f Interactive Fluorescence Dye and Filter Database] Carl Zeiss Interactive Fluorescence Dye and Filter Database. * [http://www.iss.com/resources/lifetime.html ISS Fluorescence Lifetime Standards Tables] * [http://www.iss.com/resources/probes.html ISS Fluorescence Probes Data Tables] * [http://www.fluorescence-foundation.org The Fluorescence Foundation] * [http://www.fluorophores.org Fluorophores.org The database of fluorescent dyes] * [http://www.shsu.edu/~chemistry/chemiluminescence/JABLONSKI.html Jablonski diagram] * [http://scienceworld.wolfram.com/physics/Fluorescence.html Fluorescence on Scienceworld] * [http://micro.magnet.fsu.edu/primer/techniques/fluorescence/fluorescenceintro.html Basic Concepts in Fluorescence] * [http://johnbokma.com/pet/scorpion/detection-using-uv-leds.html Scorpion detection using UV LEDs] * [http://www.confocal-microscopy.org/Protocols%20-%20Immunofluorescence.htm Immunofluorescence Protocol] * [http://www.ii.bham.ac.uk/clinicalimmunology/CISimagelibrary/ An example of use of fluorescence in generating cellular images] * [http://www.darkniteglow.com/ Difference between flourescence and glow in the dark] * [http://www.antibodypatterns.com/ More examples how the fluorescence can be used] * [http://www.betz.lu/index.php/a/2007/06/03/how_to_do_fluorescent_bodypainting_photo Fluorescence in digital Photography] * [http://www.fenskeart.com/!artist.html The Influence of Fluorescence in the World of Art] * [http://luxrerum.icmm.csic.es Fluorescence control by Photonic Crystals - ICMM] * [http://www.uvminerals.org The Fluorescent Mineral Society] * [http://www.lfd.uci.edu Laboratory for Fluorescence Dynamics] * [http://www.mcb.arizona.edu/IPC/spectra_page.htm Exitation and emmision spectra of various fluorescent dyes] [[Category:Luminescence]] [[Category:Spectroscopy]] [[Category:Fluorescence]] [[Category:Radiochemistry]] [[bn:প্রতিপ্রভা]] [[bs:Fluorescencija]] [[de:Fluoreszenz]] [[el:Φθορισμός]] [[es:Fluorescencia]] [[fr:Fluorescence]] [[gl:Fluorescencia]] [[hr:Fluorescencija]] [[it:Fluorescenza]] [[he:קרינה פלואורסנטית]] [[lt:Fluorescencija]] [[nl:Fluorescentie]] [[ja:蛍光]] [[pl:Fluorescencja]] [[pt:Fluorescência]] [[ro:Fluorescenţă]] [[ru:Флуоресценция]] [[sk:Fluorescencia]] [[fi:Fluoresenssi]] [[sv:Fluorescens]] [[tr:Floresans]] [[uk:Флюоресценція]] [[ur:تالُـّـق]] [[zh:荧光]]