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We here focus on the chiroptical response of a glutathione (GS)-protected bimetallic (AuAg)18 nanocluster containing comparable amounts of Au and Ag atoms. X-ray photoelectron spectroscopy (XPS) as well as the electrophoretic pattern allow us to determine the chemical composition of the nanocluster as Au8.5Ag9.5(SG)14. Chiroptical activity of the Au8.5Ag9.5 nanocluster is enhanced as compared to that of the corresponding monometallic Au counterpart, whereas that of bimetallic (AuAg)18 nanocluster with the atomic ratio of Au/Ag = 4.0 (Au14.4Ag3.6) decreases. Since thiolate-protected Au18 nanocluster has recently been revealed to consist of a face-fused Au9 bioctahedral kernel protected by one Au4(SR)5 tetramer, one Au2(SR)3 dimer, and three Au(SR)2 monomers, we use density functional theory (DFT) calculations to predict the lowest-energy structure of a model cluster compound Au9Ag9(SH)14 on the basis of this geometry, yielding a Agcore–Austaple intact core–shell configuration. This structure is in good agr...

Semiconductor–metal hybrid nanostructures (HNs) are promising materials for photovoltaics and photocatalysis because of their efficient charge separation in the excited state. However, analysis of their carrier dynamics has been limited to only a handful of HNs, such as CdSe–Au and CdS–Au. Herein, we synthesized and characterized PbS–Au HNs and examined their carrier dynamics by femtosecond near-IR pump–probe spectroscopy. A decrease in band-edge (1S) bleach yields was clearly observed in PbS–Au HNs as compared to PbS quantum dots (QDs) under 1S excitation, suggesting the existence of ultrafast carrier transfer from the 1S states of PbS QDs to Au nanoparticles (NPs) that was faster than the instrumental response function. A rise time analysis of 1S bleach dynamics determined that no hot carrier transfer was present. In addition to ultrafast carrier transfer, picosecond-scale carrier transfer was observed, with the rate constants increasing with Au NPs diameter. This difference between ultrafast and picose...

Chiral glutathione (GSH)-protected bimetallic Au–Ag nanoclusters (AuAg(SG)) are synthesized by the reduction of mixtures of Au and Ag salts at the feed mole ratio of Au/Ag = 3/1 in the presence of GSH and isolated by gel electrophoretic separation, yielding a family of magic-numbered bimetallic Au–Ag nanoclusters. The PAGE pattern similarity between Au(SG) and AuAg(SG) as well as the analyses based on small-angle X-ray scattering and X-ray photoelectron spectroscopy (XPS) allow comparisons of their chemical compositions for each family of nanoclusters, and the fractioned nanocluster compounds (three samples) are identified as Au12.2Ag2.8(SG)13, Au14.4Ag3.6(SG)14, and Au17.6Ag7.4(SG)18. The XPS study also suggests that (i) incorporation of Ag heteroatoms into smaller-sized Au nanoclusters is less favorable and (ii) Ag heteroatoms preferentially occupy sites on the cluster’s core (including the core-surface and center) rather than the peripheral semiring shell. Optical spectroscopy shows that the electronic...

Photoinduced electron transfer from a CdTe nanocrystal (NC) to a photoluminescence quencher, 1,2,4,5-tetracyanobenzene (TCNB), has been studied with both steady-state photoluminescence spectroscopy...

Exciton recombination dynamics of zinc-blende CdTe nanocrystals (NCs) have been investigated by using an ionic liquid as a cryogenic matrix. Size and temperature dependence of photoluminescence lifetimes of CdTe NCs were studied by time-resolved spectroscopy. The photoluminescence properties in a low-temperature range were characterized by a simple three-level model where populations of two emitting states in CdTe NCs are determined by Boltzmann distribution. Observation at low temperature suggests that the relaxation pathway is dependent on the population between two kinds of excited states of the CdTe NC generated by an electron−hole exchange interaction in the tightly confined particle-in-a-box system.

Size- and temperature-dependence of photoluminescence from CdTe nanocrystals has been studied in a room-temperature ionic liquid. With temperature decreasing from room temperature to 14 K, the photoluminescence intensity increases considerably and the emission quantum yield reaches almost 0.95 below 100 K. The emission profile below 150 K can be deconvoluted into two Gaussian peaks; one is an excitonic band and the other is a trap-related one. The temperature dependence of each band is characterized with regard to its intensity and energy. The energy splitting in the exciton fine structure of the zinc-blende CdTe nanocrystal is clearly demonstrated, and its degree can be estimated to be 5 and 13 meV for the larger (3.0 nm) and the smaller (1.9 nm) CdTe nanocrystals. The existence of the fine structure in the trap emission state and its size-dependent nature are also proposed.