Enhanced Lifetime Of Excitons In Nonepitaxial Au/cds Core/shell Nanocrystals

The ability of metal nanoparticles to capture light through plasmon excitations offers an opportunity for enhancing the optical absorption of plasmon-coupled semiconductor materials via energy transfer. This process, however, requires that the semiconductor component is electrically insulated to prevent a backward charge flow into metal and interfacial states, which causes a premature dissociation of excitons. Here we demonstrate that such an energy exchange can be achieved on the nanoscale by using nonepitaxial Au/CdS core/shell nanocomposites. These materials are fabricated via a multistep cation exchange reaction, which decouples metal and semiconductor phases leading to fewer interfacial defects. Ultrafast transient absorption measurements confirm that the lifetime of excitons in the CdS shell (tau approximate to 300 ps) is much longer than lifetimes of excitons in conventional, reduction-grown Au/CdS heteronanostructures. As a result, the energy of metal nanoparticles can be efficiently utilized by the semiconductor component without undergoing significant nonradiative energy losses, an important property for catalytic or photovoltaic applications. The reduced rate of exciton dissociation in the CdS domain of Au/CdS nanocomposites was attributed to the nonepitaxial nature of Au/CdS interfaces associated with low defect density and a high potential barrier of the interstitial phase

Enhancement of the Yield of Photoinduced Charge Separation in Zinc Porphyrin–Quantum Dot Complexes by a Bis(dithiocarbamate) Linkage

This paper describes the use of a phenyl bis­(dithiocarbamate) (PBTC) linker to enhance the quantum yield of photoinduced electron transfer (eT) from a zinc porphyrin (ZnP) molecule (donor) to a CdSe quantum dot (QD) (acceptor), where quantum yield is defined as the fraction of photoexcited ZnP molecules in the sample that donate an electron to the QD. The PBTC ligand links the ZnP to the QD by coordinating to Cd²⁺ on the surface of the QD and the Zn metal center in ZnP via its dithiocarbamate groups. Compared with the donor–acceptor complex formed in the absence of PBTC linkers, where the ZnP molecule adsorbs to the QD through its carboxylate moiety, the PBTC linkage increases the binding affinity between ZnP molecules and QDs by an order of magnitude, from 1.0 × 10⁵ ± (0.7 × 10⁴) M^–1 to 1.0 × 10⁶ ± (1.0 × 10⁵) M^–1, and thereby increases the eT quantum yield by, for example, a factor of 4 (from 8% to 38%) within mixtures where the molar ratio ZnP:QD = 1:1