Photoluminescence Enhancement of CuInS₂ Quantum Dots in Solution Coupled to Plasmonic Gold Nanocup Array

A strong plasmonic enhancement of photoluminescence (PL) decay rate in quantum dots (QDs) coupled to an array of gold-coated nanocups is demonstrated. CuInS₂ QDs that emit at a wavelength that overlaps with the extraordinary optical transmission (EOT) of the gold nanocup array are placed in the cups as solutions. Time-resolved PL reveals that the decay rate of the QDs in the plasmonically coupled system can be enhanced by more than an order of magnitude. Using finite-difference time-domain (FDTD) simulations, it is shown that this enhancement in PL decay rate results from an enhancement factor of ≈100 in electric field intensity provided by the plasmonic mode of the nanocup array, which is also responsible for the EOT. The simulated Purcell factor approaches 86 at the bottom of the nanocup and is ≈3-15 averaged over the nanocup cavity height, agreeing with the experimental enhancement result. This demonstration of solution-based coupling between QDs and gold nanocups opens up new possibilities for applications that would benefit from a solution environment such as biosensing.