Frequency upconversion activated with Lanthanide has attracted attention in various real-world applications, because it is far simpler and more effective than traditional nonlinear susceptibility-based frequency upconversion, such as second harmonic generation. However, the quantum yield of frequency upconversion of Lanthanide-based upconversion nanoparticles remains inefficient for practical applications, and spatial control of upconverted emission is not yet developed. To overcome this limitation, we developed asymmetric hetero-plasmonic nanoparticles (AHPNs) consisting of plasmonic antennae in nanocrescent shapes on the Lanthanide-based upconversion nanoparticle (UC) for efficiently delivering excitation light to the UC core by nanofocusing of light and generating asymmetric frequency upconverted emission concentrated toward the tip region. AHPNs were fabricated by high-angle deposition of gold (Au) on the isolated upconversion nanoparticles supported by nanopillars then moved to refractive-index matched substrate for orientation- dependent upconversion luminescence analysis in single-nanoparticle scale. We studied shape-dependent nanofocusing efficiency of nanocrescent antennae as a function of the tip-to-tip distance by modulating the deposition angle. Generation of asymmetric frequency upconverted emission toward the tip region was simulated by the asymmetric far-field radiation pattern of dipoles in the nanocrescent antenna and experimentally demonstrated by the orientation-dependent photon intensity of frequency upconverted emission of an AHPN. This finding provides a new way to improve frequency upconversion using an antenna, which locally increases the excitation light and generate the radiation power to certain directions for various applications.
Project end date: 08/16/17