Numerical demonstration of an efficient up-conversion enhancement strategy by plasmon excitations in a gap-mode nanocavity

Lanthanide-doped up-conversion nanoparticles (UCNPs) can be widely used as near-infrared absorbing photoactive materials in bioimaging and photovoltaic devices. However, the low absorption cross section and low luminescence quantum rate of UCNPs significantly limit its use. Therefore, a hexagonal gold pillar nano-array structure consisting of UCNPs, gold pillar arrays, gold film and silica layer is proposed. By optimizing the structural parameters, the surface plasmon resonance wavelengths are simultaneously matched with the 808 nm excitation wavelength and 450 nm emission wavelength of the UCNPs. The gap-mode nanocavity confines the incident excitation radiation to nanophotonic hotspots with greatly high field strengths, thus theoretically proposed an efficient strategy to enhance the up-conversion luminescence. The plasmonic structure investigated in this study combines the advantages of ease of processing, high absorption, low loss and good controllability of its localized surface plasmon resonance. It provides a new solution for up-conversion enhancement design of gapmode nanocavities.