Core-mantle-shell framework for optimizing the distribution and size of metallic nanoparticles in dielectric spheres on light absorption and photoelectric efficiency

Abstract

The composite structure of metallic nanoparticles and dielectric spheres, integrating metallic resonances with Mie resonance modes of dielectrics, shows great promise for efficient light absorption applications. However, the spatial distribution and size of metallic nanoparticles within dielectric spheres, aimed at maximizing optical absorption and minimizing photothermal energy loss, remain critical yet underexplored challenges. This work proposes a core–mantle–shell structure that boosts performance by incorporating metallic nanoparticles as a spherical mantle layer positioned in regions of strong electric fields induced by Mie resonances within the dielectric sphere, while enabling a fabrication process that is both straightforward and practical. With optimized spatial distribution and an increased number of nanoparticles, the average visible light absorption at the same Ag volume fraction is boosted to 2.67 times that of a single Ag particle at the sphere's center. The core-mantle-shell structure offers high flexibility in selecting core materials while allowing the shell to be porous. Based on plasmonic hot-electron charge generation and separation model calculations, Ag nanoparticles with a radius of ∼15 nm optimize photoelectric conversion efficiency, achieving 12.55 % under 1.5–3.1 eV light. The optimal metallic nanoparticle positions and sizes in core-mantle-shell structures were also consistent across other metal and dielectric materials, paralleling the results found in the SiO₂–Ag NPs-TiO₂ core-mantle-shell framework. The optimized structure, synthesized as SiO₂–Ag NPs-TiO₂ core-mantle-shell, exhibited significantly enhanced light absorption in the visible range. Compared with the SiO₂–TiO₂ core-shell, the photocatalytic degradation rate of methyl orange was improved by a factor of 4.5.