Ag-cap-enhanced upconversion luminescence of micropillars with unidirectional radiation

Exploration of plasmonic structures to enhance upconversion luminescence (UCL) attracts attention because faint UCL from a material is a bottleneck for its applications. We designed and prepared three easily realized structures to improve the UCL of β -NaYF 4 :Yb 3 , Er 3+ micropillar (MP), and compared them to a reference structure on glass on single particles. We achieved a 43-fold UCL enhancement with the MPs with an Ag cap.The experimental results and simulations indicated that the improvements in excitation field and radiation direction collectively enhanced the MP UCL. We validated the captured radiation patterns generated from various structures by excitation simulations and provide a rational criterion for cavity design.