Mechanism of whitening and quenching.

The processes of radiation absorption in a molecule and the energy release by thermal or chemical deactivation, phosphorescence, and fluorescence are outlined briefly, and the difference between fluorescent and non-fluorescent dyestuffs is discussed under physical aspects. After a description of the optical mode of action of fluorescent whitening agents (FWAs), the colorimetrical methods of characterizing FWAs and evaluating the whiteness are investigated.