Whispering Gallery Mode (WGM) microlasers were obtained by impregnating polystyrene microspheres in an aqueous solution of plasmonic nanoparticles and Rhodamine 6G. The emission spectra of Rhodamine-doped microspheres with diameters of 1 μm and 5-7 μm exhibited peaks corresponding to WGM, with a low Q-factor for 1-μm and a higher Q-factor for 5-7-μm spheres. The embedding of gold nanoparticles into microlasers results in a 40% decrease in the WGM intensity, while doping with silver nanoparticles increases it by 10%.
The hybrid nanomaterials based on inorganic matrix and organic compound with customizable properties have practical potential in the field of new developments in biological and chemical sensors, photonic and solar cell devices, as well as laser media. The optical properties of molecular clusters so called J-aggregates embedded in nanoporous aluminum oxide in presence of silver plasmonic nanoparticles were studied. The unique technique for obtaining nanoporous aluminum oxide on the island silver film was proposed. The optimal parameters of the impregnation of nanopores in the ethanol solution of pseudoisocyanine dye for the J-aggregate formation have been studied. The resonant transfer of optical energy from the oxygen vacancy in aluminum oxide to organic molecules was observed in the resulting hybrid films.
Nanoscale molecular clusters are fascinating fluorescent nanomaterials formed by highly ordered assembly of organic dyes with the optical properties strongly different from those of monomolecules. Hybrid films formed by pseudoisocyanine dye coated metal nanoparticles on a sapphire substrate or nanoporous alumina on an aluminum substrate were studied with steady‐state and time-resolved spectroscopy. On-surface reaction caused isomerization of cyanine molecules as well as self-assembly into molecular nanoclusters, so called J‐aggregates. The excitonic band of clusters had been strongly coupled to plasmonic response of metal nanoparticles. The dynamics of the strong coupling regime was directly analyzed depending on environmental conditions (temperature and presence of gas analyte). The energy transfer of the optical excitation from oxygen vacancies of alumina to the molecular clusters was observed depending on the anodization conditions of the aluminum substrate. Such unique feature should provide a new approach to develop new sensors.
The hybrid systems consisting of noble metal nanoparticles with plasmon resonances and organic cyanine dye, which are able to delocalize and migrate the energy of excitons on a large number of aggregated molecules of the structure, can be used to study the plasmon-exciton interaction. The position as well as the region of overlap of the absorption of the exciton band and the plasmon resonance of the nanoparticles in the form of island film allows observing both weak and strong coupling. The influence of overlap between the J-aggregate band of cyanine dyes with different length of the conjugation chain and nanoparticle plasmon resonance on the optical properties of hybrid structures was studied. Inhomogeneous ensembles of noble nanoparticles were obtained as an island films on the sapphire substrates by thermal deposition in vacuum. The homologous series of dicarbocyanine, monocarbocyanine and pseudoisocyanine dyes was used for forming J-aggregates in ethanol solution without adding salt by the original technique. Dye solution was spincoated on the island film to obtained hybrid structure. The plasmon resonance of the island film was broadened due to the large dispersion of the nanoparticles in size. So strong and weak plasmon-exciton coupling can be observed in hybrid structures due to overlap of the absorption bands of island film and exciton-transition in J-aggregates. The influence of near field of noble nanoparticles on enhancement of dye molecule absorption is observed in hybrid films with dicarbocyanine and monocarbocyanine. The surface molecular concentration was monitored, in the experiment there was no significant increase of the number of adsorbed molecules on island film in comparison with clean dielectric substrate. Spectral dip at the wavelength of the maximum absorption of the J-aggregate was observed for hybrid films with pseudoisocyanine.
Hybrid nanostructures that couple plasmon and exciton resonances generate hybridized energy states, which may result in unusual light-matter interactions. In our work we studied island films from the inhomogeneous ensemble of gold nanoparticles obtained by thermal vacuum deposition, spin-coated with a molecular layer of cyanine dye, in which Jaggregates were formed. The influence of the cyanine dye length chain of conjugation and the thickness of the island film on the optical properties of the hybrid structure was studied. The increase of the molecule absorption is observed for pseudoisocyanine, in comparison with mono- and dicarbocyanine dyes. The transparency in the absorption spectrum of a hybrid film with pseudoisocyanine was observed at a wavelength of 583 nm corresponding to the maximum of the Jaggregate band, which can be explained by the strong coupling of the exciton transition in the J-aggregate with the plasmon resonance of nanoparticles.
Organic nanoclusters, so-called J-aggregates, composed of cyanine dyes possess properties different from constituting molecules. There is a growing interest in the study of organic dyes conjugates with metal nanoparticles. The combination of unique properties of J-aggregates and plasmonic nanoparticles allow novel effects to be observed in such systems. The optical properties of molecular layer of cyanine dyes and its J-aggregates, coated on the island films in the form of a heterogeneous ensemble of silver or gold nanoparticles, were studied by absorption and fluorescent spectroscopy, as well as AFM. The original method for obtaining cyanine J-aggregates on metallic films without use of salt and water was developed. The molecular nanoclusters obtained on silver island film were stable for a week, while aggregation of cyanine molecules was much smaller on gold island films. The absorption spectrum of the organometallic film is not a simple sum of the spectra of its components. The absorption of dye molecules increases several times in the presence of silver nanoparticles in comparison with gold island film. Besides, the induced transparency is observed at the absorption maximum of J-aggregates, which can indicate the interaction between the plasmons of metal nanoparticles and the excitons of the J-aggregate.
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.
The molecular clusters, so called J-aggregates of pseudoisocyanine dye, were obtained in ordered cylindrical nanopores of anodic aluminum oxide. The absorption and luminescence of the samples were studied by the VIS-spectroscopy and laser confocal microscopy. The band of J-aggregates has the same shape, but is inhomogeneous broadened in comparison with solution. The luminescence maximum of J-aggregates was observed at 578 nm upon excitation at 543 nm as well as at 405 nm. Non-resonant luminescence excitation occurred due to energy transfer from oxygen vacancy of alumina to molecular nanoclusters. This is also confirmed by time-resolved luminescence spectroscopy, which shows the increase of luminescence decay time of J-aggregates placed in alumina up to the luminescence time of the clean alumina in comparison with J-aggregates coated on glass substrate.
Optical properties of cyanine dye molecules incorporated in nanotubes of natural chrysotile asbestos are studied. The absorption and fluorescence spectra of dye in asbestos have the similar shapes as in the ethanol solution, apart from small blue shift of the maxima. The Stokes shift in asbestos is smaller than in the ethanol solution. The fluorescence decay times of the dyes in asbestos nanotubes are found to be larger than that in the case of thin films of the same dyes formed on the transparent dielectric supports. This observation is rationalized in terms of the stereoisomerization hindrance in the excited electronic state of dye molecules. At the same time linear dichroism and fluorescence anisotropy observed in the experiment indicate that the embedded dye molecules are well-isolated monomer oriented predominantly along asbestos nanotubes.
The optical properties of hybrid film based on plasmon Ag nanoparticles of different size and cyanine dyes with different
length of conjugation chain depending on the relative position of the plasmon resonance and the absorption of organic
molecules were studied. The absorption spectra of the films revealed several molecular forms, such as all-trans- and cisisomers,
dimers and J-aggregate, which also exist in pure organic films without Ag nanoparticles. It’s shown that the
absorption of aggregate bands increased after exposure by nanosecond laser on the hybrid films due to photo-induced
additional self-organization of aggregates. In the presence of Ag nanoparticles, laser radiation leads to the change of
molecular forms at a comparatively low threshold.
The structural photomodification of the multicomponent cyanine films was studied. The spectrum of the film shows
different bands of components, formed by dye molecules. Optical properties of the films were determined by the relative
concentrations of the molecular forms and their orientation angles. Laser-induced changes in the absorption spectra of
film associated with the variation of the relative concentrations of the forms and their orientation angles. The dependence
of angle on the total photoexcitation energy had the form of saturating functions. Maximum limiting angles depend on
the initial orientation angles of the component.
We investigate the structural changes induced in molecular layers of dicarbocyanine by single pulse laser radiation. The successive resonance excitation of all-trans isomer causes changes of the spatial orientation and relative concentration of the different molecular forms. The dependences of relative concentration on the total energy density of the photostimulation irregularly change with single pulse energy, initial concentration of the molecules the layer, and all-trans- isomer concentration (the latter is a measure of the absorbed energy for each pulse). The model of the photostimulated structural changes in cyanine layers is suggested.
Photonic properties and photoinduced transformations of hybrid materials comprising silver nanoparticles and
polymethine dye layers were studied. Granular films were obtained via thermal evaporation of Ag on transparent
substrates in a vacuum. Polymethine dye was spin-coated over the Ag films. The samples were characterized by optical
spectroscopy, confocal fluorescent and scanning electron microscopy. Transformations of polymethine dye molecules
were studied under the action of pulsed and cw laser irradiation. The threshold of laser induced transformations of dye
molecules in hybrid films was found to be much lower than that for the bare dielectric substrate under the action of
Nd:YAG laser second harmonic pulses. In the case of a hybrid film, transformations lead to the increased absorption in
the J-aggregate band while the dye layers on a bare substrate experience, albeit 3.5 times smaller, decrease of absorption.
Enhancement of absorption and fluorescence of dyes in the fields of Ag nanoparticles was observed.
Optical properties of supported silver nanoparticles with cyanine dyes overlayers were investigated. The spectrum of the hybrid material was treated as a result of mutual interactions between the plasmon oscillations in the metal nanoparticles and resonance absorption and refraction of dye molecules. The spectral positions of the plasmon resonances are shifted due to the anomalous refraction of dye molecules while the absorption of dye molecules is enhanced due to the incident field amplification in the near field of metal nanoparticles. The photoinduced transformations of hybrid material were also observed.
We study the component composition of cyanine dye layers on different substrates (glass, mica, and sapphire) by the
absorption spectroscopy. We found that the molecular layer contains isomers of the molecules being coated and
aggregated components (dimers and J-aggregates). The relative concentrations of the components depend on the
structure of dye and its surface concentration.
The single laser pulses of several nanosecond length lead to irreversible changes in the structure of molecular nanolayers
and result in the change of the relative concentrations of the layer components.
Two types of the spatial orientation of the nanocomponents with different orientations with respect to the surface are
formed. One of these types of the orientation transforms into another type under the action of pulsed laser radiation.
The above changes were found for all the dielectric substrates studied.
Layers of carbocyanine polymethine dyes were studied to evaluate the effect exerted by the molecular structure and
thickness of a layer on its component composition. Thin layers contain cis-monomers of different structure as major
form. The number of types of cis-isomers decreases and the relative concentration of the all-trans isomers increases with
increasing thickness. As the electron-donating ability of end groups and the chain length grow, the number of
stereoisomers of different types increases. It was concluded that the equilibrium stereoisomeric composition of the layer
is determined by degree of asymmetry, which is induced in the intramolecular electron density distribution by the
interaction with substrate.
We developed the model for rearrangement of layer by heating and photoexcitation. Reversible changes in the
component composition are due to the stereoisomerization upon rotation of a molecule fragment around the second
polymethine chain bond and irreversible changes, due to the change in asymmetry of the electron density distribution
owing to irreversible spatial reorientation of layer components. The spatial reorientation of layer components is
determined by stereoisomerization upon rotations around the central bonds.
The reversible and irreversible structural transformations of monomolecular and associated nanocomponents of a
polymethine dye layer by photoexcitation or heating are studied experimentally. The photo- and thermodestruction yields
of the layers are investigated.
The effect exerted by temperature and time of heating and by a resonance photoexcitation on the relative concentration
of the molecular components of a dicarbocyanine polymethine dye layer, the rate of variation of the orientation angle of
components and its limiting value was studied. The model of the thermally and photo-induced rearrangement of the layer
is developed.
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