In organic and organic/inorganic hybrid materials, the role of the exciton reservoir (i.e., uncoupled excitons) towards populating exciton-polariton states —emerging when an excitonic transition strongly couples with a microcavity optical mode— is not well understood. Here, we identify many-body processes in the exciton reservoir by probing the time-resolved nonlinear photoluminescence of polaritons in an organic dye (1,6,7,12-bay-substituted perylene-diimide derivative) and a Ruddlesden-Popper (PEA)2PbI4 perovskite. We observe that, in the dye, exciton-exciton annihilation is hindered in the strong light-matter coupling regime and, in (PEA)2PbI4, Auger recombination obstructs the population of exciton-polaritons via radiative pumping by the emission of the exciton reservoir.
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