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 nth 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.
Keywords: aluminum nanodisk array; near-field enhancement; plasmonic lattice mode; upconversion anti-counterfeiting; upconversion luminescence.