We describe a new approach to making ultrathin Ag nanoshells with a higher level of extinction in the infrared than in the visible. The combination of near-infrared active ultrathin nanoshells with their isotropic optical properties is of interest for energy-saving applications. For such applications, the morphology must be precisely controlled, since the optical response is sensitive to nanometer-scale variations. To achieve this precision, we use a multi-step, reproducible, colloidal chemical synthesis. It includes the reduction of Tollens’ reactant onto Sn2+-sensitized silica particles, followed by silver-nitrate reduction by formaldehyde and ammonia. The smooth shells are about 10 nm thick, on average, and have different morphologies: continuous, percolated, and patchy, depending on the quantity of the silver nitrate used. The shell-formation mechanism, studied by optical spectroscopy and high-resolution microscopy, seems to consist of two steps: the formation of very thin and flat patches, followed by their guided regrowth around the silica particle, which is favored by a high reaction rate. The optical and thermal properties of the core-shell particles, embedded in a transparent poly(vinylpyrrolidone) film on a glass substrate, were also investigated. We found that the Ag-nanoshell films can convert 30% of the power of incident near-infrared light into heat, making them very suitable in window glazing for radiative screening from solar light.

Localized surface plasmons can modify linear optical responses of materials located in their vicinity. In particular, rare earth ions luminescence can be enhanced by gold nanoparticles. Luminescence exaltation is a complex phenomenon that depends on multiple parameters, a critical one being the coupling distance between the emitting species and the plasmonic core. An original multilayer nanostructure designed to precisely control the distance between the gold cores and the luminescent ions, and to study its effect on the luminescent properties is presented here. Homogeneous silica shells with controlled thicknesses adjustable from 2 to 50 nm and rare earth ion doping rates up to 2×10 20 Eu/cm 3 of silica were deposited onto gold nanospheres. These original nanostructures are then incorporated into densified sol-gel silica composites with high-optical quality. Luminescence properties are studied for increasing gold-europium (III) distances. Strong luminescence quenching is evidenced for coupling distances up to 28 nm.