Secondary emission influenced fluorescence decay of a homogeneous fluorophore solution

Comment on "Dependence of the Fluorescent Lifetime τ on the Concentration at High Dilution"

A recent Letter in this Journal (Langhals and Schlücker, J. Phys. Chem. Lett. 202213, 7568-7573) reported a dependence of the fluorescence lifetime of a dye on concentration and attributed it to "electromagnetic interactions with distant resonating structures" on a length scale of more than 100 nm. We show that their results can be explained as a straightforward result of absorption and re-emission of the fluorescence ("radiative energy transport"), which lengthens the apparent lifetime at higher concentrations. This effect has been well-documented in the literature many times. We show that simulations of the fluorescence decays accounting for radiative transport can reproduce the authors' results without postulating any new electromagnetic mechanism.