Exciton-polariton dynamics modulated by exciton-photon detuning in a ZnO microwire

In a ZnO microcavity, the exciton-polariton effect with ultralarge Rabi splitting (can be as large as several hundreds of millielectron volts) may dominate the optical properties at the energies near the band edge. Due to the light-matter coupling, the renormalized energy states, i.e., the exciton-polariton states are expected to show very different dynamical behavior compared to the free exciton state. In this work, we used a femtosecond laser to pump a high-quality ZnO whispering gallery microcavity at room temperature. In the time-resolved photoluminescence measurements, we observed that both the fast and slow decay rates of the exciton-polaritons are faster than that of the free exciton due to the strong coupling between excitons and photons in a microcavity. The decay time constants are found to depend on the exciton-photon energy detuning (delta = E-photon - E-exciton).