Cascaded Plasmon-Enhanced Emission from a Single Upconverting\nNanocrystal

Abstract

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