Linear and Nonlinear Optical Properties of Silver-Coated Gold Nanorods

Silver-coated gold nanorods (GNRs) with large longitudinal surface plasmon resonance (SPR) wavelength tunability were fabricated by depositing silver (Ag) on the surface of GNRs. Linear and third-order optical nonlinear properties together with the ultrafast response time of these nanorods were investigated. The results demonstrate that the longitudinal SPR wavelength of GNRs is very sensitive to the thickness (<i>t</i>_Ag) of the Ag coating layer, which changes the dielectric constant of the environment. As <i>t</i>_Ag increases from 0 to 15 nm, the SPR wavelength decreases dramatically from 840 to 520 nm, the corresponding wavelength-dependent third-order optical susceptibility changes dependently with the changing of the SPR absorption curve while the one-photon and two-photon figures of merit were required for optical switching applications, and the ultrafast response time also changes continuously with varying SPR wavelength. These observations are important for applications of plasmonic structures in ultrafast wavelength division multiplexing devices

Loading Cd_0.5Zn_0.5S Quantum Dots onto Onion-Like Carbon Nanoparticles to Boost Photocatalytic Hydrogen Generation

Carbon dots (C dots, size < 10 nm) have been conventionally decorated onto semiconductor matrixes for photocatalytic H₂ evolution, but the efficiency is largely limited by the low loading ratio of the C dots on the photocatalyst. Here, we propose an inverse structure of Cd_0.5Zn_0.5S quantum dots (QDs) loaded onto the onionlike carbon (OLC) matrix for noble metal-free photocatalytic H₂ evolution. Cd_0.5Zn_0.5S QDs (6.9 nm) were uniformly distributed on an OLC (30 nm) matrix with both upconverted and downconverted photoluminescence property. Such an inverse structure allows the full optimization of the QD/OLC interfaces for effective energy transfer and charge separation, both of which contribute to efficient H₂ generation. An optimized H₂ generation rate of 2018 μmol/h/g (under the irradiation of visible light) and 58.6 μmol/h/g (under the irradiation of 550–900 nm light) was achieved in the Cd_0.5Zn_0.5S/OLC composite samples. The present work shows that using the OLC matrix in such a reverse construction is a promising strategy for noble metal-free solar hydrogen production