Quenching (fluorescence)

A reduction in fluorescence caused by a process competing with photon emission, for example a collision that removes excitation energy without emitting a photon. Measuring less light because fewer excitation photons reach the sample does not by itself establish fluorescence quenching.

Loss of fluorescent population through nonemitting ground-state association. In a simple static-only case the surviving unbound emitters keep their lifetime, distinguishing it from dynamic quenching; mixtures and association-dependent spectra complicate that test.

Quenching by an excited-state encounter that introduces an additional decay rate $k_Q[Q]$. It reduces both fluorescence quantum yield and lifetime in the simple single-population model.

For purely dynamic quenching of a single emitting population, ${\Phi }_0/{\Phi }_Q={\tau }_0/{\tau }_Q=1+k_Q{\tau }_0[Q]$. The slope measures $k_Q{\tau }_0$, so determining a bimolecular quenching constant requires the unquenched lifetime or equivalent independent rate information.

An increase in fluorescence caused by reducing a quenching interaction. Dye dilution can reduce Förster resonance energy transfer; the signal alone need not identify the process that diluted the dyes.