Cascaded Plasmon-Enhanced Emission from a Single Upconverting Nanocrystal

Plasmonics has been used to enhance light–matter interaction at the extreme subwavelength scale. Intriguingly, it is possible to achieve multiple plasmonic resonances from a single nanostructure, and these can be used in combination to provide cascaded enhanced interactions. Here, we demonstrate three distinct plasmon resonances for enhanced upconversion emission from a single upconverting nanocrystal trapped in a metal nanoaperture optical tweezer. For apertures where the plasmonic resonances occur at the emission wavelengths only, a moderate enhancement of a factor of 4 is seen. However, by tuning the aperture to enhance the excitation laser as well, an additional factor of 100 enhancement in the emission is achieved. Since lanthanide-doped nanocrystals are stable emitters, this approach of using multiple subwavelength resonances can improve applications including photovoltaics, photocatalysis, and imaging. The nanocrystals can also contain only single ions, allowing for studying quantum emitter properties and applications to single-photon sources.