Surface Enhanced FluorescenceWhen a noble metal with nanostructure is irradiated with light, localized surface plasmons are resonantly generated, i.e., "plasmon resonance" occurs, which enhances various physical and chemical processes near the surface, e.g., Raman scattering or fluorescence intensities of molecules, [1][2][3][4] photoconversion efficiency of solar cell, [5,6] and yield of photochemical reactions. [7,8] Enhanced fluorescence intensity is termed surface-enhanced

A silicon nanoparticle solution (size ≅ 50 nm) with the concentration of 100 mM, which is contamination free, was synthesized using a ball milling method and was stable for 4 months without aggregation. This stability was responsible for large negative zeta potential on the surface of Si-NPs, established by milling in 2-propanol solvent.

Fluorescence-intensity enhancement of dye molecules was investigated using silicon submicron particles as a function of the particle size. Silicon particles with a size of 500 nm gave an enhancement factor up to 180. Measurement of scattering spectra revealed that the localized electric field at the particle enhances the fluorescence intensity.

Photoluminescence intensity enhancement of a silicon quantum dot solution was investigated using in situ photoluminescence/dark-field microscope spectrometer.The intensity was enhanced by Medusa-type silver particle, composed of a sphere 760 nm in diameter and many nanochains. The enhancement factor (EF) was carefully estimated, based on various corrections and finite-difference time-domain (FDTD) calculations. The EF was changed from 33 to 42,000. Spectroscopic and FDTD analyses proved valuables to evaluate local enhancement effect. Wavelength dependences of EF and scattering spectrum indicated that the enhancement is attributed to the electric field localized on particle, given by not photoluminescence light but excitation light.