Title: delayed fluorescence
Long Title: IUPAC Gold Book - delayed fluorescence
DOI: 10.1351/goldbook.D01579
Status: current

Definition
Three types of delayed fluorescence are known:   E-type delayed fluorescence: The process in which the first excited singlet state becomes populated by a thermally activated radiationless transition from the first excited triplet state. Since in this case the populations of the singlet and triplet states are in thermal equilibrium, the lifetimes of delayed fluorescence and the concomitant phosphorescence are equal.   P-type delayed fluorescence: The process in which the first excited singlet state is populated by interaction of two molecules in the triplet state (triplet-triplet annihilation) thus producing one molecule in the excited singlet state. In this biphotonic process the lifetime of delayed fluorescence is half the value of the concomitant phosphorescence.   Recombination fluorescence: The first excited singlet state becomes populated by recombination of radical ions with electrons or by recombination of radical ions of opposite charge.  

Related Terms
- annihilation: https://goldbook.iupac.org//terms/view/A00366
- biphotonic process: https://goldbook.iupac.org//terms/view/B00669
- delayed luminescence: https://goldbook.iupac.org//terms/view/D01580
- fluorescence: https://goldbook.iupac.org//terms/view/F02453
- lifetime: https://goldbook.iupac.org//terms/view/L03515
- phosphorescence: https://goldbook.iupac.org//terms/view/P04569
- radiationless transition: https://goldbook.iupac.org//terms/view/R05057
- radical ions: https://goldbook.iupac.org//terms/view/R05073
- singlet state: https://goldbook.iupac.org//terms/view/S05699
- triplet state: https://goldbook.iupac.org//terms/view/T06503

Source
- PAC, 1984, 56, 231. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-Part VI: molecular luminescence spectroscopy' on page 233 (https://doi.org/10.1351/pac198456020231)

Related References
- Orange Book, 2nd ed., p. 185 (https://media.iupac.org/publications/analytical_compendium/)
- PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2235 (https://doi.org/10.1351/pac199668122223)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/D01579/html
- json: https://goldbook.iupac.org/terms/view/D01579/json
- xml: https://goldbook.iupac.org/terms/view/D01579/xml

Citation: Citation: 'delayed fluorescence' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.D01579
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Accessed: 2026-06-29T15:03:22+00:00