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Encyclopedia > Fluorescence
Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots.

Fluorescence is a luminescence that 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 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 is named after the mineral fluorite, composed of calcium fluoride, which often exhibits this phenomenon. Image of fluorescence in various sized Cadmium Selenide Quantum Dots. ... Image of fluorescence in various sized Cadmium Selenide Quantum Dots. ... The solar corona as seen in deep ultraviolet light at 17. ... Cadmium selenide (CdSe) is a solid compound of cadmium and selenium. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... Luminescence is light not generated by high temperatures alone. ... An optical phenomenon is any observable event which results from the interaction of light and matter. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... The wavelength is the distance between repeating units of a wave pattern. ... Kinetic energy is the energy by virtue of the motion of an object. ... In physics, heat, symbolized by Q, is defined as energy in transit. ... The solar corona as seen in deep ultraviolet light at 17. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... Stokes shift Stokes shift is the difference (in wavelength or frequency units) between positions of the band maxima of the absorption and luminescence spectra (or fluorescence) of the same electronic transition. ... A fluorophore is a component of a molecule which causes a molecule to be fluorescent. ... Minerals are natural compounds formed through geological processes. ... Fluorite (also called fluor-spar) is a mineral composed of calcium fluoride, CaF2. ... Calcium fluoride (CaF2) is an insoluble ionic compound of calcium and fluorine. ...

### Physical Process

Fluorescence occurs when a molecule or quantum dot relaxes to its ground state after being electronically excited. Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... In physics, the ground state of a quantum mechanical system is its lowest-energy state. ...

Excitation: $S_0 + h nu to S_1$

Fluorescence (emission): $S_1 to S_0 + h nu$

hν is a generic term for photon energy where: h = Planck's constant and ν = frequency of light. (The specific frequencies of exciting and emitted light are dependent on the particular system.) A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... Sine waves of various frequencies; the bottom waves have higher frequencies than those above. ...

State S0 is called the ground state of the fluorophore (fluorescent molecule) and S1 is its first (electronically) excited state.

A molecule in its excited state, S1, 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. Phosphorescent powder under visible light, ultraviolet light, and total darkness. ...

Relaxation of an S1 state can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen (O2) is an extremely efficient quencher of fluorescence because of its unusual triplet ground state. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...

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 'sensitizer' molecule, which is converted to its excited state and can then fluoresce. This process is used in lightsticks. Three types of lightsticks in several colours A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. ...

### Fluorescence 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. The Quantum Yield of a radiation-induced process is the number of times that a defined event (usually a chemical reaction step) occurs per photon absorbed by the system. ...

$Phi = frac {rm # photons emitted} {rm # photons absorbed}$

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: The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ...

$frac{ { k}_{ f} }{ sum_{i}{ k}_{i } }$

where kf is the rate of spontaneous emission of radiation and Spontaneous emission is the process by which a molecule in an excited state drops to the ground state, resulting in the creation of a photon. ...

 ∑ ki i

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 inter-system crossing. Thus, if the rate of any pathway changes, this will affect both the excited state lifetime and the fluorescence quantum yield. Fluorescence resonance energy transfer (or FÃ¶rster resonance energy transfer) describes an energy transfer mechanism between two fluorescent molecules. ...

Fluorescence quantum yield are measured by comparison to a standard with known quantum yield; the quinine salt, quinine sulfate, in a sulfuric acid solution is a common fluorescence standard. Quinine is a natural white crystalline alkaloid having antipyretic, anti-malarial with analgesic and anti-inflammatory properties and a bitter taste. ...

The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. Fluorescence typically follows first-order kinetics:

$left[S_1 right] = left[S_1 right]_0 e^{ frac {-t} {tau}}$

$left[S_1 right]$ is the remaining concentration of excited state molecules at time = t, $left[S_1 right]_0$ is the initial concentration after excitation. The lifetime is related to the rates of excited state decay as:

Thus, 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). Thus, the lifetime is related to the facility of the relaxation pathway. 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. Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... A nanosecond is an SI derived unit of time equal to 10-9 of a second. ... Fluorescence resonance energy transfer (or FÃ¶rster resonance energy transfer) describes an energy transfer mechanism between two fluorescent molecules. ...

## Rules

There are several rules that deal with fluorescence. The Kasha–Vavilov rule dictates that the quantum yield of luminescence is independent of the wavelength of exciting radiation. For law within legal systems see law. ...

This is not quite 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. A Jablonski diagram is a diagram that illustrates the electronic states of a molecule and the transitions between them. ...

## Applications

There are many natural and synthetic compounds that exhibit fluorescence, and they have a number of applications:

### Lighting

The common fluorescent tube relies on fluorescence. Inside the glass tube is a partial vacuum and a small amount of mercury. An electric discharge in the tube causes the mercury atoms to emit light. The emitted light is in the ultraviolet (UV) range and is invisible, and also harmful to living organisms, so 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 over-illumination and unnatural spectra can lead to adverse health effects. Lighting refers to either artificial light sources such as lamps or to natural illumination of interiors from daylight. ... Assorted types of fluorescent lamps. ... The solar corona as seen in deep ultraviolet light at 17. ... A phosphor is a substance that can exhibit the phenomenon of fluorescence (glowing during absorption of radiation of another kind) or phosphorescence (sustained glowing without further stimulus). ... Incandescence is the release of electromagnetic radiation from a hot body due to its high temperature. ... This cosmetics store has lighting levels over twice recommended levels and sufficient to trigger headaches and other health effects Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity. ... The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. ...

In the mid 1990s, white light-emitting diodes (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 effect of apparently white light. Led is also the past tense of the verb to lead Blue, green and red LEDs. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ...

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 are highly efficient with high CRI and good color temp index rating. A spiral type compact fluorescent light bulb. ...

The modern mercury vapor streetlight is said to have been evolved from the fluorescent lamp. A Mercury Vapor Lamp is a gas discharge lamp which uses mercury in an excited state to produce light. ... A streetlight in front of a red sky at night A street light, also known as a light standard, is a raised light on the edge of a road, turned on or lit at a certain time every night. ...

Glow sticks oxidise phenyl oxalate ester in order to produce light. Three types of lightsticks in several colours A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. ... Phenyl oxalate ester, also known as Cyalume, is a liquid ester whos hydrolysis products are responsible for the luminescence in a glowstick. ...

### Biochemistry and medicine

There is a wide range of applications for fluorescence in this field. Large biological molecules can have a fluorescent chemical group attached by a chemical reaction, and the fluorescence of the attached tag enables very sensitive detection of the molecule. Examples:

• 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.
• 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 Syber 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. This is especially important in complexes of multiple biomolecules.
• Aequorin, from the jellyfish Aequorea victoria, produces a blue glow in the presence of Ca2+ 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. The structure of part of a DNA double helix. ... The chain termination or Sanger or dideoxy method is a process used to sequence (read the bases of) DNA. It is named after Frederick Sanger who developed the process in 1975. ... Ethidium bromide (EtBr) is an intercalating agent commonly used as a nucleic acid stain in molecular biology laboratories for techniques such as agarose gel electrophoresis. ... Digital printout of an agarose gel electrophoresis of cat-insert plasmid DNA Agarose gel electrophoresis is a method used in molecular biology to separate DNA strands by size, and to determine the size of the separated strands by comparison to strands of known length. ... Example of an approximately 40,000 probe spotted oligo microarray with enlarged inset to show detail. ... Fluorescent-activated cell sorting is a type of flow cytometry, a method for sorting a suspension of biologic cells into two or more containers, one cell at a time, based upon specific light scattering and fluorescent characteristics of each cell. ... Fluorescence resonance energy transfer (or FÃ¶rster resonance energy transfer) describes an energy transfer mechanism between two fluorescent molecules. ... Aequorin ribbon diagram from PDB database Aequorin is a photoprotein isolated from luminescent jellyfish (like various Aequorea species e. ... Binomial name Aequorea victoria (Murbach and Shearer, 1902) Aequorea victoria is a luminescent jellyfish found off the west coast of North America. ... GFP ribbon diagram from PDB database The green fluorescent protein (GFP) is a protein from the jellyfish Aequorea victoria that fluoresces green when exposed to blue light. ... Bilirubin is a yellow breakdown product of heme catabolism. ...

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: FLIM, FLI, FLIP, CALI, FLIE, FRET, FRAP, 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. The neck of a guitar showing the first four frets. ... FRAP: Fluorescence Recovery After Photobleaching Frap: Frap is a term used to describe movie files recorded from inside 3D computer games. ... The abbreviation FCS can stand for: Federal Commonwealth Society Federation of Conservative Students, student arm of the United Kingdoms Conservative Party. ...

### Gemology, mineralogy and forensics

Fluorescent Minerals

Many types of calcite and amber will fluoresce under shortwave UV.

Rubies, emeralds, and the Hope Diamond exhibit red fluorescence under short-wave UV light; diamonds also emit light under X ray radiation. Also, Fluorescence can be used in Chiral Recognition Ruby is a red gemstone. ... For other uses, see Emerald (disambiguation). ... Hope Diamond in museum The Hope Diamond is a large (45. ... An X-ray picture (radiograph), taken by Wilhelm RÃ¶ntgen, of Albert von KÃ¶llikers hand. ...

## Organic liquids

Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ... Phosphorescent powder under visible light, ultraviolet light, and total darkness. ... Laser-induced fluorescence (LIF) is a spectroscopic method. ... A Standard Household Light bulb This page is a list of sources of light. ... Assorted types of fluorescent lamps. ... X-ray fluorescence (XRF) is the phenomenon where a material is exposed to X-rays of high energy, and as the X-ray (or photon) strikes an atom (or a molecule) in the sample, energy is absorbed by the atom. ... Blacklight paint or blacklight-reactive paint is paint that glows under a blacklight (a source of light whose wavelengths are primarily in the ultraviolet range). ... An atomic line filter, or ALF, (sometimes atomic resonance filter or ARF) is a class of optical band-pass filters used in the physical sciences for filtering light with great precision, accuracy and efficiency. ...

Results from FactBites:

 Fluorescence - LoveToKnow 1911 (1957 words) Stokes found that the fluorescent light is not homogeneous, for on reducing the incident rays to a narrow band of homogeneous light, and examining the dispersed beam through a prism, he found that the blue light consisted of rays extending over a wide range of refrangibility, but not into the ultra-violet. Fluorescence is closely allied to phosphorescence, the difference consisting in the duration of the effect after the exciting cause is removed. The phenomenon of fluorescence can be utilized for the purpose of illustrating the laws of reflection and refraction in lecture experiments since the path of a ray of light through a very dilute solution of a sensitive substance is rendered visible.
 Olympus Microscopy Resource Center: Specialized Microscopy Techniques - Fluorescence Microscopy (2351 words) Fluorescence illumination and observation is the most rapidly expanding microscopy technique employed today, both in the medical and biological sciences, a fact which has spurred the development of more sophisticated microscopes and numerous fluorescence accessories. Fluorescence is the property of some atoms and molecules to absorb light at a particular wavelength and to subsequently emit light of longer wavelength after a brief interval, termed the fluorescence lifetime. Fluorescence Microscopy of Cells in Culture - Serious attempts at the culture of whole tissues and isolated cells were first undertaken in the early 1900s as a technique for investigating the behavior of animal cells in an isolated and highly controlled environment.
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