Defect-mediated spontaneous emission enhancement of plasmon-coupled CuInS_2 and CuInS_2/ZnS

Abstract

The studies of plasmon-coupled excitons at the surface-/interface-, shallow-, and deep-trapped states of copper-indium-disulfide (CIS) with/without zinc-sulfide (ZnS) shell revealed the defect-mediated spontaneous emission enhancement. The PL enhancement with spectral blue-shift of plasmon-coupled excitons in CIS quantum dots (QDs) indicates the large reduction of nonradiative decay at the surface- and shallow-trapped states with strong spectral overlapping. The PL enhancement with spectral red-shift of plasmon-coupled excitons in CIS/ZnS QDs is accredited to the defect-mediated PL enhancement by the higher fractional amplitude at the interface-trapped state around the longer spectral region. The spontaneous emission enhancement of plasmon-coupled CIS QDs were ~2.1, ~2.2, and ~2.8-folds compared to the decay rates of CIS, and those of plasmon-coupled CIS/ZnS QDs were ~24.1, ~32.8, and ~24.9-folds compared to the decay rates of CIS/ZnS at shorter, intermediate, and longer spectral regions due to relatively stable charge carriers and close to the surface plasmon resonance. The PL enhancements of plasmon-coupled CIS at room temperature and 6 K were two-fold and three-fold compared to the integrated CIS PLs, and the PL enhancements of plasmon-coupled CIS/ZnS at room temperature and 6 K were five-fold and eight-fold compared to the integrated CIS/ZnS PLs. The large PL enhancement is attributable to the plasmon-exciton coupling through Coulomb interaction and the local field enhancement. The larger PL enhancement of plasmon-coupled CIS/ZnS compared to that of plasmon-coupled CIS is accredited to the larger spontaneous emission enhancement.