A Plasmon Enhanced Green Luminescence of core-shell NaYF₄:Yb,Er Nanoparticles in Solid State
Robeth Viktoria Manurung1*, Surojit Chattopadhyay1,2
1Institute of Biophotonics, National Yang Ming University, Taipei, Taiwan
2Biophotonics and Molecular Imaging Research Center, National Yang Ming University, Taipei, Taiwan
* presenting author:Robeth Viktoria Manurung, email:rvmanurung@gmail.com
Lanthanide doped up-converting luminescent nanoparticles (UCNPs) are promising materials for optical bioimaging and therapy due to their unique optical and chemical properties. UCNPs, normally in organic solvent solution absorb low energy near-infrared (NIR) light and emit high-energy shorter wavelength photons. However, relatively low quantum yield prompts a need for developing methods for fluorescence enhancement. Plasmonic nanostructures are known to efficiently enhance fluorescence of the surrounding fluorophores by acting as a nanoantenna by concentrating the incident electric field into the nano-volume of the UCNPs. The synthesis of the UCNPs, NaYF₄:Yb/Er was done by thermal decomposition process which involves dissolving organic precursors in high-boiling-point solvents oleic acid (OA) and octadecene (ODE). The core–shell structure NaYF₄:Yb/Er@SiO₂ microspheres prepared by coating the NaYF₄:Yb/Er phosphors by silica as spacer via microemulsion process. Scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and photoluminescence were applied to characterize these samples. Here, we report a novel plasmon-enhanced fluorescence system in which the plasmonic absorption was tuned to achieve resonance with the excitation. Gold island films, prepared by sputtering on silicon substrates, were tuned by thickness and surface roughness to absorb at different wavelengths till a resonance was obtained at 980 nm. This resulted in a 10 fold enhancement of the green emission at 540 nm from the UCNPs in solid state.
Acknowledgments: National Science Council NSC-104-2112-M-010-002-MY3.

Keywords: Metal enhanced fluorescence, Up-conversion nanoparticles, Lanthanides, Gold island films, Surface plasmon