Tunable Black Gold: Controlling the Near‐Field Coupling of Immobilized Au Nanoparticles Embedded in Mesoporous Silica Capsules

Abstract Efficient light‐to‐heat conversion is central for various applications such as thermo‐photovoltaics and solar steam generation. Although metals can strongly absorb light and generate heat, their free electrons shield the electric field before any substantial penetration in the metal. Excitation of surface plasmons can suppress metal reflection and convert it into a black metal, for example, black gold. In this work, mesoporous silica capsules grafted with immobilized Au nanoparticles (NPs) with different sizes via controlled chemical synthesis are synthesized. It is shown that changing the size of immobilized NPs modifies the interparticle coupling strength, thus, modifying the NPs absorption. The broadness of the plasmon resonance is tuned across the visible, near‐infrared, and short wavelength infrared regions. The ability to control the broadness of black gold absorption is not possible in other systems based on bottom‐up synthesis. The proposed approach broadens the possibilities of utilizing black gold in many applications such as thermo‐photovoltaics, and solar energy harvesting especially in hybrid solar converters.