Gold nanocups with multimodal plasmon resonance for quantum-dot random lasing

Reduction of symmetry in plasmonic nanostructures may lead to great opportunities in controlling their photophysics of extinction, local field, light response, and plasmonic interactions. With their strong light scattering and unique modulation of field distribution, plasmonic nanocups hold great potential for applications in random laser, three-dimensional optical nanoantenna, and optical coherence tomography imaging. Here we demonstrate a novel and robust solution-phase synthesis approach to gold nanocups, which combines templating and seeded growth techniques to precisely control the size, morphology, and composition of the nanocups. Ripening is the key strategy in this wet-chemistry process to ensure primary anisotropic growth of gold within the cup-shaped space provided by each template, consisting of a silica nanosphere and a flexible resorcinol-formaldehyde resin shell. The resulting plasmonic nanocups possess three types of plasmon resonance modes, including axial, transverse S, and transverse P modes, determined by the polarization of the incident light. This robust and scalable synthesis allows the production of gold nanocups with high quality and efficiency, opening the door to unique photophysical properties and many potential applications, as demonstrated by their excellent performance in plasmonic quantum dot random lasing.