Localized surface plasmon

A localized surface plasmon (LSP) is the result of the confinement of a surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. The LSP has two important effects: electric fields near the particle’s surface are greatly enhanced and the particle’s optical absorption has a maximum at the plasmon resonant frequency. The enhancement falls off quickly with distance from the surface and, for noble metal nanoparticles, the resonance occurs at visible wavelengths. For semiconductor nanoparticles, the maximum optical absorption is often in the near-infrared and mid-infrared region.

The plasmon resonant frequency is highly sensitive to the refractive index of the environment; a change in refractive index results in a shift in the resonant frequency. As the resonant frequency is easy to measure, this allows LSP nanoparticles to be used for nanoscale sensing applications. Nanostructures exhibiting LSP resonances are used to enhance signals in modern analytical techniques based on spectroscopy.

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