Single Particle Studies on Two-Photon Photoluminescence of Gold Nanorod–Nanosphere Heterodimers

The localized surface plasmon resonance (SPR) property of metal nanoparticles has numerous potential applications. Coupling between different SPR modes of adjacent metal nanoparticles can result in significantly enhanced optical responses such as surface-enhanced Raman scattering (SERS) and two-photon photoluminescence (2PPL). In this work, gold (Au) nanorod (NR)–nanosphere (NS) heterodimers with side-linked and end-linked spatial arrangements have been systematically studied on the single-particle level to investigate the plasmon coupling effects on their 2PPL properties. Compared to a single Au NR, both end-linked and side-linked Au NR-NS heterodimers displayed red-shifted scattering spectra with similar cos2θ excitation polarization dependence, which can be understood in terms of plasmon hybridization theory. However, the 2PPL intensities of end-linked and side-linked Au NR-NS heterodimers displayed strikingly different excitation polarization dependence. The 2PPL signals of the end-linked Au NR-NS het...