Effect of triplet-triplet absorption on time-resolved phosphorescence

Molecular radiative transport, consisting in consecutive emission-absorption events by atoms or molecules of the same species, is studied in the case of excited-state absorption, a situation relevant to the phosphorescence of polycyclic aromatic hydrocarbons. This type of transfer differs in a number of ways from the better studied atomic resonance and molecular fluorescence cases, and leads to decays with a very distinctive form. A simple 1D model is introduced and used to discuss qualitatively the phosphorescence build-up and the phosphorescence decay in the presence of reabsorption. A new empirical phosphorescence decay law is also presented and justified on the basis of a phenomenological equation. The phosphorescence build-up and the phosphorescence decay in the presence of reabsorption are discussed and confronted with experimental results obtained for both normal and perdeuterated coronene.