Directionally enhanced photoluminescence from distributed feedback cavity polaritons

We observed the directional enhancement of photoluminescence (PL) for nonresonant excitation from cavity polaritons in the distributed feedback (DFB) waveguide microcavities when a cavity standing wave mode is resonant to an exciton. The cavities consist of a quartz grating substrate with ∼700 nm pitch, a (C₆H₅C₂H₄NH₃) ₂PbI₄ film with large exciton oscillator strength, and a polystyrene film. They are regarded as a new type of one-dimensional photonic crystals consisting of resonant dispersive materials which couple strongly to modes in the crystals. On the other hand, a dye-dispersed film on the grating does not exhibit such an enhancement, which demonstrates that the polariton effect is essential. We point out for periodic structures in the strong coupling regime that a macroscopic polarization formed under a resonant condition may-exhibit ultrafast radiative decay.