Nonlinear Dependences of Optical Properties of Spherical Core–Shell Silver–Gold and Gold–Silver Nanoparticles on Their Parameters

Modeling of nonlinear optical properties of spherical core-shell gold-silver and silver-gold nanoparticles (NPs) placed in water was carried out on the base of extended Mie theory. Efficiency cross sections of absorption σ, scattering σ, and extinction σ of radiation with wavelengths λ = 400 and 532 nm for core-shell NPs with constant core radii r = 5, 10, 20, and 40 nm and in the range of relative radii r/ r = 1-8 were calculated ( r is the radius of shell). Dependences of optical properties of gold-silver and silver-gold NPs on increasing of core radius r in the range 0 − r under condition r = const and increasing of r under r − r = const were investigated. Results show the nonlinear behavior of optical properties of core-shell gold-silver and silver-gold NPs on radiation wavelengths (optical indexes of metals), different core and shell radii, and their correlation, on relative NP radii r/ r. An increase and decrease of absorption, scattering, and extinction efficiency cross sections of core-shell NPs with changing of wavelengths, core and shell radii, and relative NP radii r/ r are established. These dependences can be used for experimental investigation of the interesting first stages of shell formation on core and optical determination of core-shell NP parameters.