Distance dependence of plasmon-enhanced fluorescence and delayed luminescence of molecular planar nanostructures

Abstract

The distance dependence of the plasmon-accelerated decay of excited singlet and triplet states of Eosin molecules was studied. Layered films of dye were prepared using the Langmuir-Blodgett technology on the surface of silver island films. The plasmon effect manifests itself in an increase in the intensity and a decrease in the lifetimes of fluorescence, delayed fluorescence and phosphorescence of the dye films with metal nanoparticles. It is shown that the optimal distance at which the maximum enhancement of all luminescence types was achieved is equal to 6–8 nm and approximately coincides with the Förster radius of the nonradiative inductive-resonance process. A proposed mathematical model is in agreement with the experimental data. From the model it is follows that the distance dependences of the long-lived luminescence intensity are qualitatively similar to the distance dependence of the fluorescence of dye molecules on the metal island films.