Upconversion in Mixed Plasmonic-Semiconductor Nanoparticle Solids

Fields generated from plasmonic particles and arrays are exploited to enhance optical and chemical processes in a wide range of fields, including nonlinear optics. Here, it is reported that in mixtures of semiconductor quantum dots and plasmonic doped oxide nanoparticles with infrared localized surface plasmon resonances, infrared excitation generates upconverted photoluminescence with a power dependence of the order less than three, in contrast to the fourth-order power-dependence expected from photon energy and observations of pure CdSe/CdS quantum dots. Earlier results of plasmonic enhancement of nonlinear upconversion have shown lower threshold fluences or powers but not a similar change in the order of power dependence, implying a different underlying mechanism in this case. The finding is reproduced in multiple sample pairs; it is observed for many different stoichiometries and for multiple pump excitation wavelengths. The anomalous power dependence is attributed to plasmon-induced saturation of quantum dot nonlinear absorption.