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 up-conversion emission from a single up-converting nanocrystal trapped by a metal nanoaperture optical tweezer. For apertures where the plasmonic resonances occur at the emission wavelength 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 quantum emitters, this approach of using multiple subwavelength resonances is promising to achieve better performance for their applications in photovoltaics, photocatalysis, single photon sources and subwavelength imaging.
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