Energy and time-resolved NIR to Visible Upconversion Luminescence from Single NaYF4:Yb3+,Tm3+Nanoparticles on Nanowire Substrates

Tm-doped energy transfer upconversion (ETU) NaYF4:Yb3+:Tm3+ nanoparticles have potential applications in deep tissue imaging and energy conversion devices due to their visible (450nm) and infra-red (800nm) upconversion emission, but suffer from low quantum efficiency. We use energy and time-resolved single particle imaging to assess the plasmonic enhancement of NIR-to-visible upconversion luminescence (UCL) from single β-NaYF4:Yb3+:Tm3+ upconverting nanoparticles (UCNPs) supported on substrates consisting of sparse arrangements of Ag nanowires. By examining the effects at the single particle level, for UCNPs strongly-coupled to nanowires, isolated UCNPs, and intermediate cases, we obtain a statistical description of UCL emission enhancement in the Tm-doped UCNPs and map out the statistical distribution of excitation and luminescence enhancement on the plasmonic substrates. We use both wide field and confocal spectroscopic imaging of single UCNPs on and off the plasmonic substrates in combination with energy and time resolved spectroscopy and compare these results to a coupled rate equation analysis to elucidate the energy transfer upconversion enhancement mechanisms.