Stokes shift is the difference (in wavelength or frequency units) between positions of the band maxima of the absorption and luminescencespectra (or fluorescence) of the same electronic transition. It is named after Irish physicist George G. Stokes. Image File history File links Stokes_shift. ... Image File history File links Stokes_shift. ... The wavelength is the distance between repeating units of a wave pattern. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Absorption, in optics, is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... Luminescence is light not generated by high temperatures alone. ... Legend: γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves: EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultrahigh frequency VHF = Very high frequency HF = High frequency... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... George Gabriel Stokes Sir George Gabriel Stokes, 1st Baronet (13 August 1819–1 February 1903) was an Anglo-Irish mathematician and physicist. ...
When a molecule or atom absorbs light, it enters an excited electronic state. The Stokes shift occurs because the molecule loses a small amount of the absorbed energy before re-releasing the rest of the energy as luminescence or fluorescence (the so-called Stokes fluorescence), depending on the time between the absorption and the reemission. This energy is often lost as thermal energy. Luminescence is light not generated by high temperatures alone. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ...
Stokes fluorescence
Stokes fluorescence is the reemission of longer wavelength (lower frequency) photons (energy) by a molecule that has absorbed photons of shorter wavelengths (higher frequency). Both absorption and radiation (emission) of energy are unique characteristics of a particular molecule (structure) during the fluorescence process. Light is absorbed by molecules in about 10-15 seconds which causes electrons to become excited to a higher electronic state. The electrons remain in the excited state for about 10-8 seconds then, assuming all of the excess energy is not lost by collisions with other molecules, the electron returns to the ground state. Energy is emitted during the electrons' return to their ground state. Emitted light is always a longer wavelength than the absorbed light due to limited energy loss by the molecule prior to emission.
Further reading
Lakowicz, J.R. 1983. Principles of Fluorescence Spectroscopy, Plenum Press, New York. ISBN 0-387-31278-1.
Guilbault, G.G. 1990. Practical Fluorescence, Second Edition, Marcel Dekker, Inc., New York. ISBN 0-8247-8350-6.
Stokesshift is the distance between the peak absorption and peak emission wavelengths.
The emitted wavelength is always longer (if single photons are absorbed) or equal to the incident wavelength, due to energy conservation; the difference is absorbed as heat in the atomic lattice of the material.
It is named after Irish physicist George G. Stokes.
This red shift is reffered to as the Stokesshift and its origin, magnitude and size dependence is a notable source of controversy, especially for silicon nanoclusters.
The figure to the left is a schematic of the Stokesshift.
The Stokesshift is the difference in energy between the initial absorption and the final emission photons.
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