Time-resolved photoluminescence of exciton-polaritons in orthorhombic TlI

Resonant photoluminescence and time-resolved photoluminescence of excitons in orthorhombic TlI have been studied at 10 K. The indirect-exciton luminescence shows an exponential decay with a lifetime of 3.0 ns. Under the resonant excitation of the direct-exciton region, multiple LO-phonon luminescence lines are observed, and have been confirmed to have a quite short lifetime (<20 ps). The dependence of scattering intensity of the multiple lines on the incident photon energy has also been investigated. The exciton relaxation process is discussed in terms of the exciton-polariton picture.