Angle-dependent optical perfect absorption and enhanced photoluminescence in excitonic thin films

We experimentally demonstrate perfect absorption of incident light in an ultrathin, planar organic layer, together with large photoluminescence (PL) enhancement. We find that diverse features appear in the absorption spectra of J-aggregate excitonic films, depending on the incident light angle and the phase controller thickness. We achieve strong absorption even away from the excitonic absorption pole. We explain the angle-dependent perfect absorption by comparing radiative and nonradiative damping rates for different incident angles. Moreover, we achieve large PL enhancement at strong light absorption conditions. This demonstrates that the absorbed light energy in excitonic perfect absorbers can be retrieved, unlike other perfect absorbers based on metal nanostructures where the absorbed energy is mainly dissipated as heat due to ohmic losses. Excitonic perfect absorbers can be useful for energy conversion devices or fluorescence-based optical devices.