Optical properties of plasmon-coupled charge carriers in CuInS$_{\mathrm{2}}$ and CuInS$_{\mathrm{2}}$/ZnS QDs

The optical properties of plasmon-coupled charge carriers in copper indium disulfide (CIS) and CIS/ZnS QDs were investigated by time-resolved and temperature-dependent photoluminescence (PL) spectroscopy. The fractional Purcell enhancement of plasmon-coupled charge carriers in CIS was observed at shorter, intermediate, and longer spectral regions. The PL lifetimes at surface-/interface-trapped states and shallow-defect states are relatively shorter than those at at deep-trapped states. The temperature-dependent PL studies revealed that the plasmon-exciton coupling reduces the PL thermal quenching, and the charges at surface-/interface-trapped states and shallow-defect states are thermally active compared to the charges at deep-trapped states. The reduction of non-radiative decays in addition to the strong local field leads to the large PL enhancement. The larger PL enhancement of plasmon-coupled CIS/ZnS in comparison with that of plasmon-coupled CIS is accredited to the significant defect-mediated Purcell enhancement for bright emission materials. The Purcell enhancement of plasmon-coupled QDs is attributable to the coupling between plasmon and defect-related carrier pairs through Coulomb interaction and the local field enhancement.