Optical properties of silver-island films having an overlayer of RhB dye

The spectra of silver-island films of different thicknesses and of RhB dye adsorbed silver films were recorded in the transmission mode using a photoacoustic spectrometer. The optical transmission spectra of discontinuous silver-island films show a different resonance peak in the spectra corresponding to the different sizes of the island particles. The overlayer of dye coat on the silver film modifies the silver resonance peak in the form of splitting and enhanced absorption. But for higher silver film thicknesses, an increase in transmission was observed on the higher wavelength side when the enhanced absorption was not dominant. In this case the dye coating acts as an antireflection coating. This unusual behavior of the dye coating occurs due to changes in dispersion and absorption of the optical response of the absorbing coating on the structural resonances of the silver island. The transmission spectra of silver-island and dye-coated films will be described by an effective medium calculation of Maxwell Garnett and by the Wang and Kerker theory for optical response.