Large-scale dewetting assembly of gold nanoparticles for plasmonic enhanced upconversion nanoparticles

Plasmonic nanostructures have been broadly investigated for enhancing many photophysical properties of luminescent nanomaterials. Precisely controlling the distance between the plasmonic nanostructure and the luminescent material is challenging particularly for the large-scale production of individual nanoparticles. Here we report an easy and reliable method for the large-scale dewetting of plasmonic gold nanoparticles onto core-shell (CS) upconversion nanoparticles (UCNPs). A commensurate NaYF4 shell with a thickness between 5 nm and 15 nm is used as a tunable spacer to control the distance between the UCNP and the plasmonic gold nanoparticles. The upconversion emission intensity of single gold decorated core-inert shell (Au-CS) UCNPs is quantitatively characterized using a scanning confocal microscope. The results demonstrate the highest feasible enhancement of upconversion emission and a record reduction in lifetime for UCNPs fabricated in this manner. The Au-CS UCNPs are further investigated by simulation and synchrotron near edge X-ray absorption fine structure (NEXAFS) analysis.