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Fluorescent minerals emitting visible light when exposed to ultraviolet light

Fluorescence is the emission of electromagnetic radiation light by a substance that has absorbed radiation of a different wavelength. In most cases, absorption of light of a certain wavelength induces the emission of light with a longer wavelength (and lower energy). However, under conditions in which intense radiation is being absorbed, it is possible for one electron to absorb two photons (multiple photon absorption), which can lead to the emission of radiation having a smaller wavelength than the excitation source. The energy difference between the absorbed and emitted photons is due to thermal losses. Dissipation of vibrational energy occurs on a much greater time scale than fluorescent emission. The most striking examples of this phenomenon occur when the absorbed photon is in the ultraviolet region of the spectrum, and is thus invisible, and the emitted light is in the visible region. Practical applications of this effect are found in mineralogy, gemology, chemical sensors, fluorescent labelling, dyes, biological detectors etc.

The term 'fluorescence' was coined by George Gabriel Stokes in his 1852 paper;[1] the name was suggested "to denote the general appearance of a solution of sulphate of quinine and similar media". (Phil. Trans. R. Soc. Lond. 1853 143, 385-396, quote from page 387). The name itself was derived from the mineral fluorite (calcium difluoride), some examples of which contain traces of divalent europium, which serves as the fluorescent activator to provide a blue fluorescent emission. The fluorite which provoked the observation originally, and which remains one of the most outstanding examples of the phenomenon, originated from the Weardale region, of northern England.











Quantum yield[edit]






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The Jablonski diagram describes most of the relaxation mechanism for excited state molecules.




For more details on this topic, see Fluorescent_light.
Fluorescent paint and plastic lit by UV tubes. Artwork by Beo Beyond


Fluorescent lights were first available to the public at the 1939 World's Fair, and 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 HID lamps coupled their even greater electrical efficiency with phosphor enhancement for better color rendition. White light-emitting diodes became available in the mid 1990s as LED lamps, 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.


Analytical chemistry[edit]


Fluorescence in several wavelengths can be detected by an array detector, to detect compounds from HPLC flow. Also, 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 lower energy atoms being excited and releasing photons, making analysis more efficient.


Main page: Fluorescence spectroscopy

Usually the setup of a Fluorescence assay involves a Light source, which may emit an array different wavelengths of light. Generally, a single wavelegth 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 transitions. To separate and analyze them, the fluorescent radiation is passed through an Emission monochromator, and observed selectively by a detector [2]

Biochemistry and medicine[edit]

Main page: Fluorescence in the life sciences

Fluorescence in the life sciences is used generally as a non-destructive way of tracking or analysis 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). In fact, a protein or other component can be "labelled" with a extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot, finding a large use in many biological applications.[3] [4]
The quantification of a dye is done with a Spectrofluorometer and finds additional applications in:

  • when scanning the fluorescent intensity across a plane one has 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. Labeling multiple antibodies with different fluorophores allows visualization of multiple targets within a single image (multiple channels). DNA microarrays are a variant of this.

. Ethidium bromide fluoresces orange when intercalating DNA and when exposed to UV light.

  • FACS (fluorescent-activated cell sorting)
  • 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 may be carcinogenic - an arguably safer alternative is the dye SYBR Green.

Additionally Fluorescence resonance energy transfer used to study protein interactions, detect specific nucleic acid sequences and used as biosensors, while fluorescent lifetime can give an additional layer of information.

Gemology, mineralogy, geology, and forensics[edit]

Fingerprints can be visualized with fluorescent compounds such as ninhydrin. Blood and other substances are sometimes detected by fluorescent reagents, particularly where their location was not previously known.

Gemstones, minerals, fibers, and many other materials which may be encountered in forensics or with a relationship to various collectibles may have a distinctive fluorescence or may fluoresce differently under short-wave ultraviolet, long-wave ultra violet, or X-rays.




Organic liquids[edit]


Further reading[edit]

  • Lakowicz, J.R. 2006. Principles of Fluorescence Spectroscopy, Third Edition, Plenum Press, New York. ISBN 0-387-31278-1.
  • Valeur, B. 2001. Molecular Fluorescence: Principles and Applications, Wiley-VCH. ISBN 352729919X .
  • Guilbault, G.G. 1990. Practical Fluorescence, Second Edition, Marcel Dekker, Inc., New York. ISBN 0-8247-8350-6.


  2. Harris, D. C. et al, Exploring Chemical Analysis 4th ed., New York, NY (c)2009 by W.H. Freeman and Company
  3. Lakowicz, J.R., Principles of fluorescence spectroscopy. 3rd ed. 2006, New York: Springer. xxvi, 954 p.