The difference (usually in frequency units) between the spectral positions of the band maxima (or the band origin) of the absorption and luminescence
arising from the same electronic transition. Generally, the luminescence
occurring at a longer wavelength
than the absorption is stronger than the opposite. The latter may be called an anti-Stokes shift.
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2278
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook