Stokes shift

Stokes shift
Name	Stokes shift
Field	Spectroscopy; Photophysics; Photochemistry

Stokes shift The Stokes shift is the spectral difference between absorbed and emitted photons in luminescent materials, relevant to Isaac Newton, George Gabriel Stokes, William Henry Perkin, and institutions such as the Royal Society and Royal Institution. It appears across systems studied at Harvard University, University of Cambridge, Massachusetts Institute of Technology, California Institute of Technology, and in technologies developed by RCA Corporation and General Electric.

Definition and basic principles

The Stokes shift describes the wavelength or frequency displacement between an excitation band and an emission band observed in spectroscopy experiments performed at facilities like Lawrence Berkeley National Laboratory and Max Planck Society centers. In photophysics and photochemistry investigations at Princeton University and ETH Zurich, it is characterized using instruments from Shimadzu Corporation, PerkinElmer, and Agilent Technologies. The concept underpins spectroscopy taught at University of Oxford, Stanford University, and University of Tokyo and is central to analyses in journals such as Nature Photonics, Science, and Journal of Chemical Physics.

Mechanisms and origins

Explanations for the Stokes shift draw on work from researchers associated with Royal Society of Chemistry, American Chemical Society, and theoretical frameworks developed at Institute for Advanced Study and Los Alamos National Laboratory. Mechanistic contributions include vibrational relaxation described using models from Linus Pauling-inspired molecular orbital theory, solvent reorganization framed by Onsager-type continuum approaches, and electronic relaxation pathways investigated in studies at Bell Labs and IBM Research. Nonradiative decay channels invoked in protein fluorophore studies at Max Planck Institute for Biophysical Chemistry and National Institutes of Health labs illustrate energy redistribution processes that produce emission shifted relative to absorption.

Measurement and units

Quantification of the Stokes shift is routinely performed using spectrophotometers and fluorometers produced by Thermo Fisher Scientific and PerkinElmer in laboratories at Yale University and Columbia University. The shift may be reported in nanometers (nm), electronvolts (eV), or wavenumbers (cm−1), conventions employed in publications from American Physical Society, Royal Society, and European Physical Journal. Calibration standards and procedures are documented by bodies such as International Organization for Standardization and used in metrology labs like National Institute of Standards and Technology and Physikalisch-Technische Bundesanstalt.

Applications and examples

Large and small Stokes shifts find application in fluorescence microscopy at centers like Janelia Research Campus and Howard Hughes Medical Institute, flow cytometry instruments by BD Biosciences, and organic light-emitting diode programs at Samsung Electronics and Sony Corporation. In biological assays at Scripps Research and pharmaceutical firms like Pfizer and Roche, Stokes shift considerations guide dye selection for green fluorescent protein derivatives engineered by teams including those at University of California, Berkeley and European Molecular Biology Laboratory. In materials science, perovskite photovoltaics researched at National Renewable Energy Laboratory and quantum dot displays from Nanosys exploit Stokes-shift engineering to improve performance. Examples include fluorophores such as coumarins, rhodamines, and cyanines studied at University of Illinois Urbana–Champaign and Columbia University Irving Medical Center.

Factors affecting Stokes shift

Environmental and molecular determinants are investigated in collaborations involving CERN-adjacent research groups and university consortia including Imperial College London and University of California, San Diego. Solvent polarity effects characterized following approaches by Yves Chauvin-influenced protocols, temperature dependence measured with cryostats developed at Oxford Instruments, and matrix effects studied in polymer labs at Dow Chemical Company and DuPont. Conformational dynamics probed using time-resolved spectroscopy at Argonne National Laboratory and ultrafast lasers from Coherent, Inc. reveal how intramolecular vibrations and intermolecular interactions modulate the magnitude of the shift.

Related phenomena and comparisons

Phenomena related to the Stokes shift are explored alongside resonant Raman scattering studied by teams at Brookhaven National Laboratory, Kasha's rule formulated in discussions involving Michael Kasha and institutions like Columbia University, and anti-Stokes emissions observed in thermographic phosphors used by NASA and European Space Agency. Comparisons are made with phenomena such as Förster resonance energy transfer analyzed at Max Planck Institutes and nonlinear upconversion processes developed by groups at Fujifilm and Nikon Corporation.

Category:Spectroscopy