Optical properties of layered composite materials consisting of plasmonic nanostructures and semiconductor quantum dots (QDs) have been investigated both experimentally and theoretically. It was demonstrated that in the case of spectrally overlapping bands of plasmonic absorption and fluorescence of alloyed QDs placed directly onto silver island film, the fluorescent intensity increases. While in other samples with alloyed QDs the fluorescence was not sensitive to silver nanoparticles or even quenched by silver nanoparticles for core-shell QDs. That was explained by resonant and non-resonant interaction of QDs with the near fields of plasmonic structures. Measuring the fluorescence decay time, we observed a clear correlation between the fluorescence intensity of alloyed QDs and reducing fluorescent lifetime in the case of resonant interaction or the Purcell effect. The interaction between excitons in semiconductor material and plasmons in metal nanoparticle was explored also in the Zn-ZnO system via numerical modeling. This system is interesting because metal films may be easily created via magnetron sputtering on silica glass substrates and then fully or partially oxidized in the course of thermal annealing in air. Thus a core-shell nanostructure consisting of a semiconductor shell with promising chemical sensor properties (ZnO) and metallic core with the plasmon resonance in the same spectral region (Zn) will be created.
The optical properties of organometallic films of silver nanoparticles and J-aggregates of pseudoisocyanine dye have been studied to observation of the plasmon-exciton interaction. The original method for obtaining J-aggregates on inhomogeneous island silver films without use of salt and water was developed. Owing to the broad bandwidth of inhomogeneous plasmon resonances; it is possible to study the interaction of nanoparticles and J-aggregates, obtained in the spin-coated layer on the silver island film. The absorption spectrum of the organometallic film is not a simple sum of the spectra composing its components. The absorption of dye molecules increases several times in the presence of silver nanoparticles, which is due to the influence of the near fields of the latter. The spectral dip in the absorption maximum of the J-aggregate of pseudoisocyanine was observed; it became more symmetrical with an increasing equivalent thickness of the island film.
Several coherent light sources with dimensions less than the diffraction limit were proposed and demonstrated in the last decade. One of the most popular of them is a spaser. Since its theoretical proposal, there were a number of experimental realizations based on metal nanoparticle colloids and laser dyes. However, the disaffection with these realizations grows as the conditions of the performed experiments were too close to that of the random-lasing phenomena. Hence, an experiment with a refined setup that greatly reduces an unintended feedback due to the multiple scattering events is in order. In this work, we achieved this goal by creating a monolayer of metal nanoparticles on the solid surface and cover them with a thin layer of dye molecules.
Optical properties of composite structures comprised of the island films of silver nanoparticles with a thin molecular layer of a dye rhodamine 6G were obtained and studied in this paper. In the near field of plasmonic nanoparticles enhancement and shifting of the maximums of the absorption and fluorescence spectra were observed. In the absorption and fluorescence spectra of thin molecular films with nanoparticles the new red-shifted band in comparison with spectra of thin films without nanoparticles was found. This band was associated with the formation of aggregates. Thus, the silver nanoparticles can contribute to fluorescence enhancement and formation of the aggregates in the rhodamine thin films.
We strive to obtain highly fluorescent planar materials that may be used for the development of nanolasers based on localized plasmons. The promissing candidates for this purpose are materials consisting of mixtures of organic molecules, polymer, and silver nanoparticles. Silver nanoparticles were preliminary deposited on the quartz substrates. These samples were characterized by SEM and absorption spectroscopy. Then, they were covered by the polymer/rhodamine and polymer/coumarin layers using either spin-coating or evaporation techniques and characterized by confocal luminescent microscopy and spectroscopy. As a result of the localized surface plasmon excitation, we observed the enhancement of the rhodamine and coumarine absorption in the near fields of silver nanoparticles. The fluorescence of the thin films of polymer activated by dyes molecules with silver nanoparticles was almost 20-fold more intense than that on the bare dielectric surfaces without silver nanoparticles. In the presence Ag nanoparticles and at increased intensities of excitation we found also slight narrowing of the luminescence spectrum of polymer/coumarin layers.
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