Quinton Rice

Time-resolved and temperature-dependent photoluminescence of ternary and quaternary nanocrystals of CuInS2 with ZnS capping and cation exchange

Time-resolved and temperature-dependent photoluminescence (PL) spectroscopy of ternary compound copper indium disulfide (CuInS2, or CIS) core materials, CIS/ZnS coreshells, and quaternary compound ZnCuInS2 (ZnCIS) revealed their optical properties with spectral, temporal, and thermal characteristics, which were closely linked to surface-related recombination, and shallow or deep defect-related donor-acceptor transitions. The PL peaks of semiconductor nanocrystals (SNCs) with sizes near Bohr radius displayed at ∼775 nm for CIS, ∼605 nm for CIS/ZnS, and ∼611 nm for ZnCIS. The spectral blue shift and spectral narrowing with CIS/ZnS and ZnCIS are assigned to the increased spatial confinement and surface regularity with the etching of core materials. Both the shorter lifetime at surface-trapped states or interface states and the longer lifetime at intrinsic defect-related states of CIS, CIS/ZnS, and ZnCIS SNCs were widely distributed across the entire PL spectral region. The surface or interface-trapped electr...

Defect-mediated spontaneous emission enhancement of plasmon-coupled CuInS 2 and CuInS 2 /ZnS

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.

Fractional contributions of defect-originated photoluminescence from CuInS 2 /ZnS coreshells for hybrid white LEDs

The wide optical tunability and broad spectral distribution of CuInS2/ZnS (CIS/ZnS) coreshells are key elements for developing the hybrid white light emitting diodes where the nanoparticles are stacked on the blue LEDs. Two CIS/ZnS555 nm and CIS/ZnS665 nm coreshells are utilized for the hybrid white LED development. The time-resolved spectroscopy of CIS/ZnS555 nm and CIS/ZnS665 nm reveals the correlation between the fast, intermediate, and slow decay components and the interface-trapped state and shallow-and deep-trapped states, although the fractional amplitudes of photoluminescence (PL) decay components are widely distributed throughout the entire spectra. The temperature-resolved spectroscopy explains that the PL from deep-trapped donor-acceptor (DA) state has relatively large thermal quenching, due to the relative Coulomb interaction of DA pairs, compared to the thermal quenching of PL from interface defect state and shallow-trapped DA state. A good spectral coupling between the blue diode excitation and the PL from CIS/ZnS leads to the realization of hybrid white LEDs.

Plasmon-Coupled CdSe/ZnS and CdTe/CdS/ZnS Coreshells for Hybrid Light Emitting Devices.

Plasmon-coupled CdSe/ZnS and CdTe/CdS/ZnS coreshells are investigated for their optoelectronic applications because of their high color purity, wide optical tunability, large PL enhancement, and compact and easy integration into electronic devices. The quantum confinement of carriers within quantum dots (QDs) with sizes near the exciton Bohr radius (CdSe ~ 5.8 nm, CdTe ~ 7 nm) exhibits the features of discrete energy states and blue-shift from the bulk bandgap (CdSe ~718 nm, CdTe ~ 863 nm) in the optical spectrum. While the fluorescence from the QDs is attributable to the exciton carrier recombination, large PL enhancement and fast emission time is achieved through plasmon-exciton coupling via the Coulomb interaction. Large PL enhancement of QDs in the vicinity of plasmonic particles was observed and attributed to the reduction of the non-radiative decay rate and large local field enhancement. The large PL enhancement and wide optical tunability along with high color purity from plasmon-coupled QDs enables the realization of hybrid LEDs.