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Stokes Shift Stokes shift ticular molecular structure. If a material has a direct bandgap in the range of visible light, the light shining on it is absorbed, causing electrons to become excited to a higher energy state. The electrons remain in the ex- cited state for about 10−8 seconds. This number varies over several orders of magnitude depending on the sam- ple, and is known as the fluorescence lifetime of the sam- ple. After losing a small amount of energy in some way (hence the longer wavelength), the molecule returns to the ground state and energy is emitted. 2 References Absorption and emission spectra of Rhodamine 6G with ~25 nm [1] Gispert, J.R. (2008). Coordination Chemistry. Wiley- Stokes shift VCH. p. 483. ISBN 3-527-31802-X. [2] Albani, J.R. (2004). Structure and Dynamics of Macro- Not to be confused with Stark shift. molecules: Absorption and Fluorescence Studies. Elsevier. p. 58. ISBN 0-444-51449-X. Stokes shift is the difference (in wavelength or frequency [3] Lakowicz, J.R. 1983. Principles of Fluorescence Spec- units) between positions of the band maxima of the troscopy, Plenum Press, New York. ISBN 0-387-31278- absorption and emission spectra (fluorescence and Raman 1. being two examples) of the same electronic transition.[1] [4] Guilbault, G.G. 1990. Practical Fluorescence, Second It is named after Irish physicist George G. Stokes.[2][3][4] Edition, Marcel Dekker, Inc., New York. ISBN 0-8247- When a system (be it a molecule or atom) absorbs a 8350-6. photon, it gains energy and enters an excited state. One [5] Kitai, A. (2008). Luminescent Materials and Applications. way for the system to relax is to emit a photon, thus los- John Wiley and Sons. p. 32. ISBN 0-470-05818-8. ing its energy (another method would be the loss of heat energy). When the emitted photon has less energy than [6] Rost, F.W.D. (1992). Fluorescence Microscopy. Cam- the absorbed photon, this energy difference is the Stokes bridge University Press. p. 22. ISBN 0-521-23641-X. shift. If the emitted photon has more energy, the en- ergy difference is called an anti-Stokes shift;[5] this ex- tra energy comes from dissipation of thermal phonons 3 See also in a crystal lattice, cooling the crystal in the process. Yttrium oxysulfide doped with gadolinium oxysulfide is a • Stokes line common industrial anti-Stokes pigment, absorbing in the near-infrared and emitting in the visible portion of the • Jablonski diagram spectrum. Photon upconversion is another anti-Stokes • process. Kasha’s rule 1 Stokes fluorescence Stokes fluorescence is the re-emission of longer wave- length photons (lower frequency or energy) by a molecule that has absorbed photons of shorter wavelengths (higher frequency or energy).[6] Both absorption and radiation (emission) of energy are unique characteristics of a par- 1 2 4 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 4 Text and image sources, contributors, and licenses 4.1 Text • Stokes shift Source: http://en.wikipedia.org/wiki/Stokes%20shift?oldid=596292446 Contributors: Smack, Charles Matthews, Lfh, Seth Ilys, BenFrantzDale, Mykhal, V8rik, Srleffler, Supten, Kkmurray, Somoza, Sbyrnes321, SmackBot, Eskimbot, Pedrose, Stichte, Thijs!bot, Pjvpjv, D.H, Gumby600, KylieTastic, Pdcook, SieBot, Man It’s So Loud In Here, Brewcrewer, Alexbot, Dchamberss, Walkman16, Addbot, Jacopo Werther, LaaknorBot, RedBot, EmausBot, Wyang, ChuispastonBot, Widr, Helpful Pixie Bot, Sobarwiki and Anonymous: 22 4.2 Images • File:Stokes_shift-_Rh6G.png Source: http://upload.wikimedia.org/wikipedia/commons/3/3f/Stokes_shift-_Rh6G.png License: Public domain Contributors: Own work Original artist: Sobarwiki 4.3 Content license • Creative Commons Attribution-Share Alike 3.0.
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