High-Quality Dual-Plasmonic Au@Cu_2–xSe Nanocrescents with Precise Cu_2–xSe Domain Size Control and Tunable Optical Properties in the Second Near-Infrared Biowindow

Dual-plasmonic Au–Cu2–xE (x > 0, E = S, Se, Te) hybrids present multifunctionalities for broad applications in photovoltaics, photocatalysis, and biomedicine. However, despite the increasing interest in these dual-plasmonic Au–Cu2–xE hybrids, precise control over the morphology and size of their substituents is crucial but greatly challenging. Herein, a selenium-mediated two-step synthetic approach is developed to prepare the Au@Cu2–xSe nanocrescents with precise control over their size and tunable plasmonic properties through varying the concentration of the SeO2 precursor. The complete encapsulation of the Au domain within the Cu2–xSe layer in the nanocrescent in an asymmetric manner enables the strong coupling between their substituents, significantly enhancing their optical properties supported by both experimental results and theoretical modeling. The increasing Cu2–xSe domain size enables the tuning of carrier densities and thereby molar extinction coefficients corresponding to the respective visible and near-infrared (NIR) plasmon bands of the Au@Cu2–xSe nanocrescents. Electron transfer from the Au to Cu2–xSe domains is unambiguously determined in the Au@Cu2–xSe nanocrescents by transient absorption (TA) and extinction spectral measurements. The Cu2–xSe-dependent bleaching amplitude and carrier dynamics of both visible and NIR plasmon TA signals are observed, along with variations of the carrier–phonon and phonon–phonon relaxation processes. This work not only presents a facile synthetic approach of high-quality dual-plasmonic Au@Cu2–xSe nanocrescents and a fundamental understanding of the coupling mechanism in the Au–Cu2–xSe hybrid system, but also provides a paradigm for the study on the interplay in a dual-plasmonic metal–semiconductor system.