Over 104–fold enhancement of red–color upconversion luminescence of NaYF4:Yb,Er nanoparticles dispersed on a plasmonic metal structure

Plasmonic enhancement of upconversion luminescence (UCL) of lanthanide ions has been extensively studied, in which plasmonic resonance modes are designed to match either excitation or emission wavelength of the UCL. Thus, the UCL is improved by resonant enhancement of the local excitation field or emission rate of the UCL due to the Purcell effect. In this work, we fabricated a compound metallic structure consisting of a grating structure decorated with annealing–formed Ag particles (AgPs) and additionally covered with a metal (Ag) layer, to enhance the UCL of NaYF 4 :Yb,Er nanoparticles dispersed on it. By utilizing localized surface plasmon resonance (LSPR) modes at the AgPs (LSPR–1) and nanocavities at the foot–corner of the AgPs (LSPR–2), as well as Bloch–type surface plasmon resonance (SPR) modes in the periodic structure, green– and red–UCL of the upconversion nanoparticles (UCNPs) are resonantly enhanced for 10 3 – 4 folds. Particularly, as the Bloch–type SPR mode matches the red–UCL band and the LSPR–2 mode matches the excitation wavelength, the red–UCL is enhanced up to over 10 4 –fold (e.g., 13272), a record–high level for the UCL of a large number of UCNPs dispersed on a photonic structure. The large enhancement factor is mainly attributed to cooperative enhancement of both the local excitation field and emission rate of the UCL photons in multiple resonance conditions. The method of utilizing multi–resonance modes in compound structures to enhance the UCL can also be used to enhance interactions of light and matter in other systems and develop highly efficient optoelectronic devices.