Optical Properties of Small Silver Particles

Abstract

The optical absorption of very small silver particles in glass was measured as a function of particle size and temperature. The shape of the measured absorption band was Lorentzian, as required by the simple free-electron theory, and the position of the band was close to that calculated from the optical properties of bulk silver. The width of the absorption band was inversely proportional to the particle radius, showing that the mean free path of the electrons was determined by the particle size. The absorption band for particles much smaller than the mean free path of the electrons was little changed from room temperature to 500°C; however, for larger particles the band broadened somewhat with increasing temperature.