Nanoparticles of I-III-VI semiconductors are promising candidates for novel non-toxic fluorescent materials. However, removal of defect levels responsible for their broad-band emission has not been successful to date. The present study demonstrates, for the first time, the coating of core AgInS 2 nanoparticles-one of the I-III-VI group semiconductors with a bandgap in the visible region-with III-VI group semiconductors. The AgInS 2 /InS x and AgInS 2 /GaS x (x = 0.8-1.5) core/shell structures generate intense narrow-band photoluminescence originating from a band-edge transition at a wavelength shorter than that of the original defect emission. Microscopic analyses reveal that the GaS x shell has an amorphous nature, which is unexpected for typical shell materials such as crystalline lattice-matching ZnS. Singleparticle spectroscopy shows that the average linewidth of the band-edge photoluminescence is as small as 80.0 meV (or 24 nm), which is comparable with that of industry-standard II-VI semiconductor quantum dots. In terms of photoluminescence quantum yield, a value of 56% with nearly single-band emission has been achieved as a result of several modifications to the reaction conditions and post-treatment to the core/shell nanoparticles. This work indicates the increasing potential of AgInS 2 nanoparticles for use as practical cadmium-free quantum dots.
Homogeneously alloyed bimetallic particles of AuPd with an average size of ca. 2 nm were successfully prepared by simultaneous sputter deposition of Au and Pd in an ionic liquid in the absence of any additional stabilizing agents. The chemical composition of the AuPd alloy was tunable depending on the area fraction of Au plates in the Au-Pd binary targets for sputtering. The particles were immobilized on an HOPG surface by heat treatment along with the increase in the average size of particles from ca. 2 nm to ca. 7 nm. Ionic liquid species adsorbed on the as-prepared AuPd nanoparticle films on HOPG caused the prevention of electrocatalytic reactions, but repetition of potential sweep cycling in a basic aqueous solution removed the adsorbed ionic species, resulting in electrocatalytic oxidation of ethanol at the AuPd alloy nanoparticle-immobilized HOPG electrode. The electrocatalytic activity of AuPd nanoalloy particles varied upon changing the fraction of Au and Pd in the particles, and alloy particles having an Au fraction of ca. 0.61 exhibited the maximum activity against ethanol oxidation, being higher than the activity of the pure Pt surface.
Positively charged CdS nanoparticles having diameter of 3.0 ± 0.2 nm were prepared by the chemical
modification of their surfaces with thiocholine. Chains of size-quantized CdS nanoparticles were prepared by
using the electrostatic interaction between positively charged nanoparticle surfaces and the phosphate groups
of DNA molecules. The observation by transmission electron microscopy revealed that the CdS nanoparticles
were arranged in a quasi one dimension with dense packing. The line width of a nanoparticle array was equal
to the diameter of CdS nanoparticles that was ca. 3.0 nm. The average distance between the centers of the
adjacent nanoparticles was estimated to be 3.5 nm, which was almost equal to the length of 10 base pairs in
DNA double strands.
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