Scalable preparation of highly homogeneous plasmonic gold nanocubes and their application in strong light–matter coupling

Abstract

Plasmonic gold nanocubes (AuNCs) are highly promising for nanophotonic and plasmonic applications due to their intense localized surface plasmon resonances (LSPRs). However, achieving scalable production of homogeneous AuNCs with reproducible optical properties remains challenging. Here, we introduce a centrifugal depletion‐induced flocculation (CDF) method that yields AuNCs with exceptional uniformity and high recovery (98–99%) within 20–60 minutes. By carefully optimizing centrifugation parameters and depletion‐agent concentrations, we effectively remove synthetic impurities, resulting in nanoparticles with significantly reduced spectral linewidths and high structural uniformity. Using the AuNCs, we demonstrate strong plasmon–exciton coupling with molecular J-aggregates: the hybrids exhibit clear spectral splitting and anti-crossing behavior characteristic of the strong-coupling regime. Notably, smaller AuNCs show stronger coupling due to their higher quality factors and reduced mode volumes. Moreover, implementing a layer‐by‐layer (LBL) coating strategy of J-aggregates on AuNCs further enhances the coupling strength by approximately 21%, as confirmed by experimental measurements and computational modeling. Our approach offers a versatile, scalable route to producing uniform polaritonic nanostructures, enabling their application in advanced optical and quantum‐photonic technologies. © 2025 SPIE. All rights reserved.