Light Absorption and Scattering Spectra of Nanoparticles with a Bimetallic Au/Ag Core and an Outer Shell with Two J-Bands of Molecular Aggregates

We report our results on light absorption and scattering cross sections of composite spherical nanoparticles with a bimetallic core and an outer shell of molecular aggregates of cyanine dyes exhibiting two excitonic resonances. Calculations have been performed within the framework of the extended Mie theory by taking into account the frequency-dependent and size-dependent dielectric functions of gold and silver. It is shown that for such three-layer particles, a specific regime of strong plasmon-exciton coupling is achieved, when the induced transparency effect is manifested simultaneously at two different wavelengths. The spectral distance between two identified dips of induced transparency turns out to be 150 nm.