Non-Linear Density Dependent Upconversion Luminescence Enhancement of beta-NaYF4: Yb3+: Er3+ Nanoparticles on Random Ag Nanowire Aggregates

Spectroscopic imaging and statistical analysis of NIR-to-visible upconversion luminescence (UCL) from beta-NaYF4: Yb3+: Er3+ upconverting nanoparticles (UCNPs) supported on a series of random Ag nanowire aggregates reveals a density dependent UCL enhancement. Statistical analysis of the spectrally resolved upconversion images shows a non-linear dependence of upconversion luminescence enhancement with Ag nanowire surface coverage. A maximum average enhancement of 5.8x was observed for 58% surface coverage. Based on the empirically determined trend with density, it is estimated that up to 20x upconversion luminescence enhancement can be achieved at 100% surface coverage, even at high excitation intensity. This projection is commensurate with the 20x enhancement ratio observed for select locations within the imaged micro-ensemble. Time-resolved emission of the UC luminescence from UCNPs on the Ag nanowire aggregates confirms the surface plasmon effects on the UCNPs kinetics. Such Ag nanowire aggregates show potential as a scalable and relatively simple metal-enhanced upconversion substrate.