Silver island films, monomolecular polymer layers and fluorescent collector dyes - their characterisation and electromagnetic interaction

Improvement of the flourescent quantum yield and chemical stability of bathochromic organic dyes was the aim in studying their interaction with small silver particles in a polymer matrix. Analysis of the individual components and synthesis in the composite system were the two main approaches adopted. The silver island film was modelled as a collection of oblate spheroids which was characterized by a log-normal distribution of the axial ratios, allowing its optical characteristics to be derived. The following layer, consisiting of monomolecular films of octadecyl maleimide, was applied with the Langmuir-Blodgett technique. Its properties were studied on the basis of interference in reflection and transmission. Dipolar properties of the fluorescent collector dye molecules were obtained from analysis of the flourescence lifetime measurements and the spectra for absorption and fluorescence. The electric potential for the system consisting of silver, polymer and dye was derived as a sum of dipolar and higher order multipolar components. From this, expressions for the rates of radiative and non-radiative decay were obtained. Their quotient for a given spectral range depends on the extent to which surface plasmons are excited in the silver spheroid, which in turn is determined by the size and eccentricity of the spheroid. The more oblate the spheroid is, the longer the wavelength is at which the resonance condition is fulfilled.