Thin films of organic dyes with silver nanoparticles: enhancement and spectral shifting of fluorescence due to excitation of localised surface plasmons

Localised surface plasmon resonances of silver nanoparticles were used for modification of spectral response of organic dye thin films. Silver nanoparticles were deposited in the form of an island film on the quartz substrate. Three kinds of organic thin films with different absorption spectra were used: coumarin, rhodamine, and malachite green. A prominent increase of the thin films absorption was observed. Along with the enhancement of the dye absorption, shifts of the plasmon frequencies were observed. In the presence of silver nanoparticles either fluorescence quenching or enhancement was observed depending on the thickness of the dye layers. In the presence of silver nanoparticles maximum of the dye fluorescence shifts by 30 nm. To enhance the fluorescence of organic thin films we used poly(methyl metacrylate) as a matrix isolating molecules from the metallic surface. In this case, five-fold enhancement of the dye fluorescence was registered.