Alexander A. Chistyakov

Interaction of CdSe/ZnS core-shell semiconductor nanocrystals in solid thin films

The optical properties of CdSe/ZnS semiconductor nanocrystals with the core-shell structure are studied upon visible-laser excitation in a wide range of flux densities. It is demonstrated that the dimensional quantization effect is preserved in the films with a limiting high concentration of nanocrystals. A strong bathochromic shift of the absorption and luminescence peaks relative to the peak positions in the corresponding spectra of nanocrystals in films with a relatively low concentration of nanocrystals and solutions is caused by a high concentration of nanocrystals and the dipole moment related to the asymmetry of the nanoparticles. The shift is varied from 35 to 50 nm depending on the film thickness. The luminescence spectra of the films remain unchanged upon an increase in the laser intensity to 1 × 106 W/cm2. The laser action on the nanoparticle films is studied at intensities (5 × 106−1 × 109 W/cm2) higher than the damage threshold.

A laser desorption ion-mobility increment spectrometer for detection of ultralow concentrations of nitro compounds

A compact instrument that implements for the first time a method for analyzing substances, in which laser desorption of analyzed molecules and laser ionization of an air sample are combined with the ionmobility increment spectroscopy, is described. Pulse radiation of the fourth harmonic of a portable (2.6 kg) GSGG: Cr3+: Nd3+ laser (λ = 266 nm) is used. The detection limit of the developed laser desorption spectrometer of the ion-mobility increment is 40 pg for trinitrotoluene (TNT), and the linear dynamic range for TNT is 0.1–20.0 ng. The results from detection of nitro compounds are presented: trinitrotoluene, cyclotrimethylene trinitramine (RDX), and octogen (HMX). It is shown that laser desorption of nitro compounds from a metal is accompanied by their decomposition on the surface and emission of fragments. An ion signal is obtained for nitro compounds that were ionized outside the spectrometer.

Two-photon-induced Förster resonance energy transfer in a hybrid material engineered from quantum dots and bacteriorhodopsin

Energy transfer from nanostructures to biological supramolecular photosystems is an important fundamental issue related to the possible influence of nanoobjects on biological functions. We demonstrate here two-photon-induced Förster resonance energy transfer (FRET) from fluorescent CdSe/ZnS quantum dots (QDs) to the photosensitive protein bacteriorhodopsin (bR) in a QD-bR hybrid material. The two-photon absorption cross section of QDs has been found to be about two orders of magnitude larger than that of bR. Therefore, highly selective two-photon excitation of QDs in QD-bR complexes is possible. Moreover, the efficiency of FRET from QDs to bR is sufficient to initiate bR photoconversion through two-photon excitation of QDs in the infrared spectral region. The data demonstrate that the effective spectral range in which the bR biological function is excited can be extended beyond the band where the protein itself utilizes light energy, which could open new ways to use this promising biotechnological material.

Hybrid heterostructures based on aromatic polyimide and semiconductor CdSe quantum dots for photovoltaic applications

A nanohybrid photoactive material based on aromatic polyimide (PI) doped with CdSe quantum dots (QDs) has been developed to be used in photovoltaic solar cells. The solar cell is based on a heterostructure of an ITO electrode covered with a layer of Cu–phthalocyanine and a layer of a PI–QD composite. The photovoltaic properties of the CuPc/PI:CdSe hybrid heterostructure at various QD concentrations in the PI matrix have been studied. Luminescent and transmission electron microscopy analyses have shown that the optimal QD mass concentration is 60%. The efficiency of the solar cell based on optimized PI:CdSe structures approaches those for the structures based on conventional MEH-PPV organic semiconductor. Moreover, the photovoltaic characteristics of the solar cell remain stable in the air for a long time (120 h). This is expected to considerably simplify the technology of manufacturing these hybrid solar cells. The mechanisms of the excitation and charge transfer from QDs to the organic semiconductors and...

Luminescence of europium-doped BaO-Bi2O3-B2O3 glasses

We have prepared europium-doped BaO-Bi2O3-B2O3 glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω2, Ω4, and Ω6), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for 5D0 → 7FJ transitions.

A laser ion-mobility spectrometer

The process of ion-packet broadening in a longitudinal laser spectrometer of ion mobility is studied. The contributions of the diffusion, Coulomb, and other broadening mechanisms are compared. The resolution of the developed spectrometer was measured (R ∼ 45) in atmospheres of both purified air and pure nitrogen. The dependence of the spectrometer resolution on the drift voltage was studied. The recorded spectra of a number of molecules of explosives with an extremely low pressure of saturated vapors indicate a high sensitivity of the developed spectrometer (no worse than 10−14 g/cm3).

Laser-induced photoprocesses in solutions and films of the CdSe/ZnS nanoparticles

The photophysical properties of solutions and films with relatively high concentrations of CdSe/ZnS nanoparticles are studied in the presence of the visible laser irradiation in a wide range of power densities. The short-wavelength wing detected in the photoluminescence spectra of the solutions of quantum dots is due to the selective laser excitation of small-size nanoparticles. A comprehensive analysis of the anti-Stokes photoluminescence of the nanoparticles in solutions and films indicates the thermal mechanism of this phenomenon. The dimensional quantization effect, narrow spectra, and a relatively high luminescence yield are retained in the films with a high nanoparticle concentration. The luminescence spectra of the films remain unchanged when the laser flux density increases to 1 × 106 W/cm2. The effect of the laser radiation on the nanoparticle films is studied at the flux densities exceeding the damage threshold (5 × 106–1 × 109 W/cm2).

Photoluminescence of CdSe/ZnS quantum dots in a porous silicon microcavity

It is known that manufacturing and applications of photonic crystals is currently an area of much interest. One of the focuses of special attention in this area is various microcavity (MC) devices. Porous silicon is one of the most promising materials for manufacturing such devices because it is simple to prepare, its optical parameters are precisely controllable, and it has an enormous surface area. This allows to inject different kinds of luminophores into porous silicon MC devices. Apparently, semiconductor quantum dots (QDs) are among the most interesting of them. QDs are characterized by a wide absorbance spectrum, large absorption cross-section, high quantum yield, and excellent photostability. To date, there have been few studies on QD injection into porous silicon photonic structures. In addition, many structures used lack the desired characteristics; the depth of QD penetration also remains a question. This is the first study to analyze the photoluminescence spectrum and kinetics of QDs in a high-quality porous silicon MC. A drastic narrowing of the luminescence spectrum has been observed after QD injection. We have found that the MC morphology considerably affects the penetration of QDs. The kinetics of photoluminescence has also been investigated. Measurements have shown a decrease in the QD characteristic photoluminescence decay time after QD injection into a porous silicon MC compared with the QD photoluminescence decay time in a toluene solution. However, we have not observed a significant difference between the photoluminescence decay times of QDs in an MC and in single-layer porous silicon.

Intracavity laser field asymmetric ion mobility spectrometer for highly efficient detection of organics

A new optical multipass scheme for laser field asymmetric ion mobility spectrometry (FAIMS) has been proposed and implemented. The scheme and the gas-analyzer system developed include both intracavity multiphoton laser ionization and FAIMS detection of the analyte. The computation and experimental results show multifold growth of the laser intensity in the FAIMS ion source, as well as the amplitude of ion signal. The gas phase detection threshold achieved is estimated to be 10?14 to 10?15?g?cm?3. Further development of the proposed approach is discussed.

A laser spectrometer of field-asymmetric ion mobility

A method for analyzing a substance has been experimentally tested. The method combines the field-asymmetric ion mobility spectrometry and laser ionization of molecules under atmospheric pressure. Pulsed radiation of the fourth harmonic of an YAG: Nd3+ laser (λ = 266 nm) and a spectrometer with a cylindrical analysis camera were used. The results of detecting nitrocompounds—trinitrotoluene, cyclotrimethylenetrinitramine (hexogen, RDX), etc.—are presented. The experimental detection limits of the spectrometer are 5 × 10−15 g/cm3 (cyclotrimethylenetrinitramine) and ≤3 × 10−15 g/cm3 (trinitrotoluene).