Exciton-phonon scattering and photoexcitation dynamics in J-aggregate microcavities

We have developed a model accounting for the photoexcitation dynamics and the photoluminescence of strongly coupled J-aggregate microcavities. Our model is based on a description of the J-aggregate film as a disordered Frenkel exciton system, in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. In a strongly coupled microcavity exciton polaritons are formed, mixing super-radiant excitons and cavity photons. The calculation of the microcavity steady-state photoluminescence, following a cw nonresonant pumping, is carried out. The experimental photoluminescence intensity ratio between upper and lower polariton branches is accurately reproduced. In particular, both thermal activation of the photoluminescence intensity ratio and its Rabi splitting dependence are a consequence of the bottleneck in the relaxation, occurring at the bottom of the excitonic reservoir. The effects due to radiative channels of decay of excitons and to the presence of a particular set of discrete optical molecular vibrations active in relaxation processes are investigated.