Stimulated emission of dye molecules coupled to localized plasmons in Ag nanoparticles

Optical properties of silver nanoparticles are determined by the excitation of localized plasmon oscillation. These oscillations result in the appearance of strong local electromagnetic fields near the nanoparticles. Of... [ view full abstract ]

Optical properties of silver nanoparticles are determined by the excitation of localized plasmon oscillation. These oscillations result in the appearance of strong local electromagnetic fields near the nanoparticles. Of particular interest is the possibility of creating coherent nanosized light sources such as a spaser. In this contribution, lasing properties of the structures based on organic dye layer and 2D silver nanoparticles ensemble are explored.

The fluorescence spectra of the organic coumarin thin films with and without silver nanoparticles were measured at excitations by pulses of the third harmonic of a Nd-YAG laser at different energy. While at low pump energies fluorescence intensity was proportional to the pump energy in both samples, at larger pump energies their behavior was completely different. The fluorescence intensity of the dye layer was saturated. Contrary to that the fluorescence intensity of dye with silver nanoparticles was not saturated. Moreover, after a threshold, it grew even faster than at smaller pump pulse energies. Also, in the presence of silver nanoparticles, strong narrowing of the fluorescence band with the growing pumping energy was observed.

Thus, two basic features of stimulated emission, namely the spectral line narrowing and the superlinear nonsaturated dependence of the luminescence intensity on the pumping energy had been observed.