Stokes shift

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Stokes shift is the difference between positions (expressed in terms of energy, wavenumber or frequency) of the spectral band maxima of the absorption and emission spectra (fluorescence and Raman being two examples) of the same electronic transition. It is named after Irish physicist George Gabriel Stokes. When a system (be it a molecule or atom) absorbs a photon, it gains energy and enters an excited state. The system can relax by emitting a photon. The Stokes shift occurs when the energy of the emitted photon is lower than that of the absorbed photon, representing the difference in energy of the two photons. The Stokes shift is primarily the result of two phenomena: vibrational relaxation or dissipation and solvent reorganization. A fluorophore is a part of a molecule with a dipole moment that exhibits fluorescence. When a fluorophore enters an excited state, its dipole moment changes, but surrounding solvent molecules cannot adjust so quickly. Only after vibrational relaxation do their...

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