A study was carried out and a comparative analysis of the spectral-kinetic (absorption and fluorescent) characteristics of nanospheres containing luminescent inorganic quantum dots (QDs) CdSe/ZnS, covered with an amphiphilic polymer shell, which ensures the stability of nanospheres in aqueous colloidal solutions and the possibility of introducing into them hydrophobic photochromic diarylethene molecules with different structure. Photoinduced reversible isomerization of diarylethene molecules causes modulation of the photoluminescence signal of quantum dots, including through the control of the efficiency of resonant energy transfer (FRET) from quantum dots to the cyclic isomer of diarylethene. The FRET efficiency turned out to be the highest in nanospheres with DAE2 and DAE4. The value of the quality index (QF) of the FRET photomodulator (which shows the efficiency of modulation of the quantum yield of QD photoluminescence), introduced in this work, varies for samples with different diarylethenes from 0.003 (for DAE1) to 0.09 (for DAE2). Nanospheres containing luminescent nanoparticles of various shapes can be used in the development of luminescent photocontrolled panels, fluorescent markers, etc.

The results of studies of the spectral-kinetic (absorption and fluorescent) characteristics of the polymer nanospheres created by us (containing luminescent inorganic CdSe/ZnS quantum dots and photochromic diarylethene molecules) incorporated into a polymer film are presented. A reversible modulation of the fluorescence intensity of quantum dots, caused by the photoisomerization of diarylethene molecules, was found. It is shown that nanospheres in polymer matrices exhibit higher efficiencies of both photoinduced modulation of QD radiation and Förster resonance energy transfer (FRET) from QDs to the cyclic isomer of DAE as compared to solutions. The results can be used, for example, to create luminescent photocontrolled panels based on films containing fluorescent nanoparticles.

A comparative analysis of photoluminescence quenching of CdSe colloidal quantum dots, nanorods, and nanoplatelets under external electric field has been carry out. Experimentally it has been demonstrated that for the quantum dots the PL quenching is more efficient than in the same nanorods and nanoplatelets. The functional dependence of PL intensity quenching vs. magnitude of electric field has been established and is in good accordance with the probability of charge tunneling under a triangular potential barrier.

It is shown that a hybrid nanocomposite structure can be created by integration of semiconducting materials with different dimensionalities: an array of quasi-1D GaAs whisker nanocrystals formed by molecular-beam epitaxy on a Si (111) substrate and 0D PbS colloidal quantum dots. The morphological and spectral properties of the resulting system are analyzed.

The anisotropy of the optical properties of CdSe quantum nanoplates is investigated, using the methods of absorption spectroscopy. It is experimentally established that the optical properties of the quantum nanoplates are anisotropic. Spectral dependences are obtained for the absorption anisotropy of ensembles of nanocrystals ordered in a stretched polymer film. A technique has been developed for creating elastic polymer films made from polyvinyl butyral with a high concentration of quantum nanoplates. (C) 2013 Optical Society of America.

We have studied complexes between CdSe/ZnS quantum dots and metal-free porphyrin molecule in aqueous solution and in human blood plasma. We have established that in aqueous solution, transition of the porphyrin to a stable form occurs 2-5 h after formation of the complexes. We have observed that the porphyrin molecules react with the components of the blood plasma, which hinders direct formation of complexes between them and quantum dots in this medium. When previously prepared complexes between quantum dots and porphyrin molecules are added to the blood plasma, they partially dissociate. In aqueous solutions and in human blood plasma, we observe efficient intracomplex transfer of the photoexcitation energy from the quantum dots to the porphyrin molecules.

The methods of luminescence microscopy have been used to study the morphology of self-organized structures composed of CdTe and CdSe/ZnS quantum dots obtained during the controlled drying of solutions of these substances on hydrophilic and hydrophobic surfaces. Local concentrations of quantum dots that are appreciably smaller than is possible when they are close-packed are estimated in dendritic structures. It is found that additional components of the solution of quantum dots can independently form dendritic structures in which the quantum dots can be incorporated. Based on an analysis of the luminescence spectra, it is shown that the quantum dots become spatially separated by size in various types of structures.

We have studied the electrical and optical characteristics of cells filled with nematic liquid crystal (NLC) based on cyanobiphenyls with positive dielectric anisotropy, containing dispersed 3.5-nm-sized CdSe/ZnS composite semiconductor nanoparticles (quantum dots, QDs) with a concentration of 0.1–0.2 wt %. In addition to a decrease in the threshold voltage of the electrooptical splay effect, the doping with QDs leads also to a decrease in the phase delay of light and the effective dielectric permittivity of NLC cells. These characteristics are reduced by half during the storage of NLC cells containing about 0.2 wt % QDs, which is related to the self-organization of QDs.

Liquid-crystal (LC) composites based on a combination of different acrylates and pentylcyanobiphenyl and containing CdSe/ZnS semiconductor quantum nanorods have been investigated. Samples of electro-optical cells with planar or homeotropic structures (depending on the acrylate type) have been obtained. The morphology of LC composite formation has been studied using luminescence techniques. It is shown that these composites are gel-like LC media, where the formation of dispersed and network structures in the cells plays a stabilizing role. The role of the electron transfer reactions during polymerization and the features of the kinetics of the Freedericksz effect (reorientation in an electric field) are discussed.

The revealed absorption saturation and Fresnel diffraction of ultrashort laser pulses under resonant excitation of the basic exciton transition in CdSe/ZnS quantum dots (a strongly absorbing colloidal solution) have been explained by the processes of filling of states of a two-level system with the excited-state lifetime dependent on the light intensity and self-diffraction of the laser beam due to the formation of the transparency channel and the induced diaphragm.

A dissociative luminescent sensor for Ni 2+ , Co 2+ , and H + ions in water solutions has been developed. This sensor is a complex made up of luminescent semiconductor hydrophobic CdSe/ZnS quantum dots (QDs) with azo-dye l-(2-pyridylazo)-2-naphthol (PAN). The luminescent properties of these complexes are investigated in organic solutions and in polymer matrixes. It is shown that the QD/PAN complex can be used for the quantitative luminescent analysis of Ni 2+ , Co 2+ , and H + ions in water solutions with a significantly higher sensitivity than that of the traditional colorimetric methods of analysis.

We have demonstrated a difference in the nature of the effect of a strong external electric field (>105 V/cm) on the photoluminescence of cadmium selenide nanoparticles of different shapes. We have determined a correlation between the magnitude of the external electric field and the average photoluminescence decay time for two types of nanoparticles: "quantum dots" and nanorods. We discuss the mechanism for the effect of an electric field on the photoluminescence of both types of nanoparticles.

The fluorescence of CdSe/ZnS nanorods in liquid-crystal and anisotropic polymer composites is studied. A high degree of the fluorescence anisotropy is shown. It is found that a solubilizer strongly affects the CdSe/ZnS orientation, which opens new possibilities for creating electrically controlled liquid-crystal composites.

We have developed a method for solubilization of hydrophobic CdSe/ZnS nanocrystals of the core/shell type, obtained by high-temperature synthesis in coordinating organic solvents. The method is based on chemical modification of the surface of the nanocrystals with hydrophilic organic mercapto compounds. We have observed that long-chain mercaptoundecanoic acid molecules effectively protect the surface of CdSe/ZnS nanocrystals in water, increasing (compared with short-chain molecules) the photostability of the nanocrystals.

We have studied enhancement of the fluorescence of fluorescein isothiocyanate (FITC), bound to albumin and near an annealed silver island film, as a function of the distance between the protein molecules and the metal. As the intermediate spacer layer between the albumin and the silver substrate, we used multilayer films based on polyelectrolytes. The maximum nine-fold enhancement coefficient for the fluorescence of FITC corresponds to a thickness of the intermediate layer of ≈4 nm, or three layers of the polyelectrolyte. In this case, we observe a significant decrease in the average photoluminescence decay time for the label near the silver film compared with a dielectric medium.

A study is made of the photodegradation kinetics of luminescence and absorption of cadmium sulfide nanocrystals incorporated into a plastic polymer matrix. The reversibility effect of photodegradation under mechanical deformation (stretching) of a polymer film is revealed. It is suggested that the photodegradation reversibility is related to the extraction of electrons, photoexcited in nanocrystals, from deep-lying traps in the surrounding polymer matrix during its deformation.

The pump-and-probe method was used in the picosecond range to study nonlinear absorption in oxidised CuInS2 nanocrystals (of 3 nm radius) embedded in a polymer film. Oxidation gave rise to an additional absorption band with its maximum at 1.03 eV. This band was bleached by excitation with laser pulses of the 1.08 μm wavelength. Fast (∼ 50 ps) capture of carriers by deep trapping states resulted in long-lived (in excess of 300 ps) bleaching and induced absorption. An energy level diagram was proposed for oxidised CuInS2 nanocrystals.

Picosecond absorption spectroscopy was used in an investigation of nonlinear optical processes in nanostructured composites based on polytungstic acid, which were photocoloured by preliminary UV irradiation. The absorption bands responsible for the photocoloration and associated with intervalent charge transfer were bleached by the action of powerful laser pulses. The characteristic monoexponential relaxation time of the process was ~300 ps. The results obtained were analysed taking account of the special features of the splitting of the energy levels of tungsten ions with different degrees of oxidation and of delocalisation of the valence states within separate elements of the polytungstic acid structure.