Up-to-Five-Photon Upconversion from Near-Infrared to Ultraviolet Luminescence Coupled to Aluminum Plasmonic Lattices.

The incorporation of upconversion luminescence (UCL) materials into various plasmonic structures promotes light-matter interactions in nanophotonic systems. It has been experimentally demonstrated that UCL enhancement entailing two photons exhibits a quadratic dependence on the excitation intensity. However, in the field of plasmonics, there have not been sufficient studies on high-order multi-photon upconversion processes. We report up-to-five-photon UCL, wherein λ = 1550 nm near-infrared light is converted to 382 nm ultraviolet light, from core-inert shell nanoparticles coupled to aluminum plasmonic lattices. The five-photon UCL intensity of nanoparticles on the plasmonic lattice is over 800 times stronger than that on the flat glass. We demonstrate that the enhancement of UCL scales with the n th power of the local field enhancement for n -photon process. These findings give a strategy to obtain high-order multi-photon UPL with aluminum plasmonic nanostructures and can contribute to anti-counterfeiting application.