Surface plasmon enhanced up-conversion from NaYF4:Yb/Er/Gd nano-rods.

The surface plasmons that are enabled by grating coupling in two-dimensional gold nano-particle arrays (AuNPAs) affected the spectral characteristics of the up-conversion (UC) emission from Yb(3+)-Er(3+)-Gd(3+) co-doped sodium yttrium fluoride (NaYF4:Yb/Er/Gd) nano-rods. The red emission of NaYF4:Yb/Er/Gd nano-rods at 660 nm (excited with a 980 nm diode laser) was significantly enhanced by the interaction with the AuNPAs. The geometric characteristics of the gold nanoparticles influenced the position of the surface plasmon resonance, and their near field strengths. The intensity of the red emission normalized versus the green emission reached 1.4, measured against a reference film in the absence of the metallic nanostructures. The lifetime for the green and red emission decreased steadily as the periodicity decreased (relative to the reference), reaching about 6% reduction for the 350 nm AuNPA. A qualitative agreement was obtained between the experimental results and finite difference time domain (FDTD) calculations.