Surface plasmon polariton enhanced upconversion in rare earth doped nano crystals on plasmonic substrates

Plasmonic enhancement of near infra-red to visible upconversion could potentially yield high-efficiency spectral converters for solar cells. We use spectroscopic imaging to investigate the intensity enhancement and modification of radiative rates of infra-red to visible upconversion from rare-earth doped nanoparticles (NaYF₄:Yb:Er[Tm]) supported on substrates designed to support a surface plasmon polariton at frequencies which are near-resonant with the rare-earth sensitizer (Yb³⁺) absorption. Using spatially-resolved spectroscopic imaging, we directly observe a systematic enhancement in the efficiency of upconversion associated with the interaction of the co-doped nano-particles with the plasmonic substrates. Spectrally resolved reflectivity and time-resolved luminescence decay measurements support our interpretation.