Twinned-Au-tip-induced growth of plasmonic Au–Cu Janus nanojellyfish in upconversion luminescence enhancement.

The twinned nanotip of the Au nanoflower and the large lattice mismatch between Au and Cu can induce formation of twin defects during the growth process, resulting in asymmetric deposition of Cu atoms. [Display omitted] The metallic Janus nanoparticle is an emerging plasmonic nanostructure that has attracted attention in the fields of materials science and nanophotonics. The instability of the Cu nanostructure leads to very complex nucleation and growth kinetics, and synthesis of Cu Janus nanoparticle has challenges. Here, we report a new method for synthesis of Au–Cu Janus nanojellyfish (JNF) by using twinned tips of Au nanoflower (NF) as seeds. The twinned nanotip of the Au NF and the large lattice mismatch between Au and Cu can induce formation of twin defects during the growth process, resulting in asymmetric deposition of Cu atoms. The symmetry-breaking using different sizes of Au NF and Cu nanodomains within the Au–Cu JNF can controllably change the localized surface plasmon resonance (LSPR) modes. The asymmetric Au–Cu JNF can induce plasmon coupling between dipolar and multipolar modes, which leads to clear electric-field enhancement in the near-infrared region. An Au–Cu JNF with multiple LSPR modes was chosen to simultaneously match the excitation and emission bands of the lanthanide-doped upconversion nanoparticles (UCNPs). A 5000-fold enhancement of the upconversion luminescence was achieved by using single plasmonic Au–Cu JNF. The Au–Cu JNF can also provide a guide for new metallic Janus nanoparticles in the fields of plasmonic, photothermal conversion, and nanomotors. [ABSTRACT FROM AUTHOR]