title: Optical investigation of gold shell enhanced 25 nm diameter upconverted fluorescence emission.
abstract: We enhance the efficiency of upconverting nanoparticles by investigating the plasmonic coupling of 25 nm diameter NaYF4:Yb, Er nanoparticles with a gold-shell coating, and study the physical mechanism of enhancement by single-particle, time-resolved spectroscopy. A three-fold overall increase in emission intensity, and five-fold increase of green emission for these plasmonically enhanced particles have been achieved. Using a combination of structural and fluorescent imaging, we demonstrate that fluorescence enhancement is based on the photonic properties of single, isolated particles. Time-resolved spectroscopy shows that the increase in fluorescence is coincident with decreased rise time, which we attribute to an enhanced absorption of infrared light and energy transfer from Yb(3+) to Er(3+) atoms. Time-resolved spectroscopy also shows that fluorescence life-times are decreased to different extents for red and green emission. This indicates that the rate of photon emission is not suppressed, as would be expected for a metallic cavity, but rather enhanced because the metal shell acts as an optical antenna, with differing efficiency at different wavelengths.
authors.affiliation: Department of Physics, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Kory
authors.initials: K
authors.lastname: Green
authors.forename: Janina
authors.initials: J
authors.lastname: Wirth
authors.forename: Shuang Fang
authors.initials: SF
authors.lastname: Lim