Vol 125, No 5 (2018)

The problem of transfer of line radiation in sodium vapor under photoexcitation by laser radiation of a resonance line with wavelength λ = 589.6 nm is numerically solved. The influence of Doppler frequency shifts on photon emission coherent in the atomic reference system is taken into account in the formation of an emission line profile using the model of partial frequency redistribution. In the case of a small optical thickness of a medium τ₀ ≤ 1, the Doppler frequency redistribution in the laboratory reference system yields higher intensity values in the emission line profile core in comparison with the model of complete frequency redistribution. For an optically dense medium, thermal motion of atoms leads to an increase of reabsorption in the emission line core, and intensity increases in the line wings as compared to the complete redistribution model. The dependence of the Holstein trapping factor on optical thickness is closer to the analytic dependence than the complete redistribution model. This is explained by the fact that the frequencies of emitted photons in the laboratory reference system fall into the spectral profile core, which increases the effects of resonance radiation trapping in a dense medium.

The title compound 2-Benzylidenehydrazinecarbothioamide was grown and the optimized molecular geometry was generated using density functional theory. Experimental Fourier transform Raman and infrared spectra were recorded and compared with the calculated results. The normal mode frequencies, Infra red and Raman intensities were computed with the Becke three Lee–Yang–Parr 6-31/G* method. Normal coordinate analysis is employed to analyze and interpret the vibrational assignments in the experimental spectra. The second harmonic efficiency of the grown crystal was studied by Kurtz and Perry powder reflection technique.

The spectral and kinetic characteristics of the emission of Sn- and Fe-doped Ga₂O₃ crystals excited by a nanosecond electron beam are studied. A new cathodoluminescence band of the Fe-doped crystal is revealed with a maximum at λ_m = 315 nm. Comparison with the data obtained with a subnanosecond duration of the beam current pulse is performed. It is shown that, with increasing duration of the beam current pulse, the main contribution is made by cathodoluminescence in the range of 300–450 nm.

The influence of the molecular weight of polyvinylpyrrolidone on the structure and the spectral and nonlinear optical properties of composite materials (sols and coatings) containing CdS/ZnS nanoparticles is experimentally studied. Cd/ZnS nanoparticles were obtained by a liquid colloid-chemical method in the presence of polyvinylpyrrolidone. It is found that the size of polyvinylpyrrolidone molecules strongly affects the size of forming chalcogenide particles, as well as the structure and the spectral properties of mat-erials.

Expressions for determining the optical characteristics of a monolayer of homogeneous monodisperse spherical particles under normal illumination by a plane electromagnetic wave with arbitrary polarization and nonpolarized radiation have been obtained. They are based on the quasi-crystalline approximation (QCA) of the theory of multiple scattering of waves (TMSW) and the multipole decomposition of fields and the tensor Green function in terms of the vector spherical wave functions. The influence of the polarization state of the incident wave on the angular structure of the radiation that is scattered by a partially ordered monolayer and a monolayer with a imperfect lattice has been considered.

For the first time, it is demonstrated that the magnitude and sign of the effect of “spectral condensation” of a laser pulse at the resonant-transition frequency of a dense medium can be controlled by changing the driving-pulse parameters (chirp, pulse width, and pulse amplitude). In the process of this, importantly, the driving-pulse energy and spectrum remain unchanged. Direct time-resolved measurements revealed an oscillatory character of the induced superradiance of rubidium vapors representing a long train of decaying short pulses. The width and repetition rate of the pulses in the train are determined by atomic density N₀ of the medium, while the width of an entire superradiance pulse (10 ps) is considerably larger than that of the driving laser pulse (50 fs).

The spectral optical characteristics of polymer composite nanomaterials based on carbon nanotubes (CNTs) in a high-density polyethylene (HDPE) matrix have been measured. The obtained experimental data have been compared with calculated data. The single-frequency model of the Lorentz oscillator is proposed for use as the theoretical model. It has been shown that samples with a carbon nanotube concentration of 10 wt % in a high-density polyethylene matrix provide high optical absorption of 90 ± 1% in the whole measured range from 300 to 800 nm. CNT–HDPE-based polymer composite nanomaterials may find practical applications in different devices of optical radiation attenuation and photoacoustics.

The possibility of precision measurements of frequencies of forbidden transitions of cold atoms in a trap using stimulated Raman scattering is shown. Transition 1S–2S in a hydrogen atom, in which the atom passes from level 1S to level 2S via intermediate level 3P is considered in detail. In this case, the frequency of the pump field (103 nm) is close to the frequency of the 3P–1S transition, while the stimulated scattering frequency (656 nm) is close to the frequency of the 3P–2S transition.

Nanosprings represent an advanced group of nanocrystals with chiral design, as well as much functionality due to their chemical and optical properties. In particular, their helical shape provides high optical activity. In this paper we suggest a quantum-mechanical theory to describe the optical activity of semiconductor nanosprings. Specific attention is given to the interaction of the left-handed and right-handed circular polarized light with nanosprings. The developed model shows that the spectrum of dissymmetry factor can be tuned by varying the geometric parameters of nanosprings.

Of primary interest for the design of novel optoelectronic devices are densely packed ordered arrays of quantum dots (QDs), which can be produced via self-assembly or other nanofabrication techniques. In such arrays, also known as supercrystals, the interaction between the QDs results in a collective optical response. Despite the active research on arrays made of perovskite QDs, a rigorous theory of their collective excitations is still lacking. In this paper, we develop a quantum-mechanical theory of Frenkel excitons in planar perovskite QD arrays with square lattice.

Semiconductor quantum dots (QDs) are characterized by orders of magnitude higher multiphoton linear absorption cross-sections compared with conventional organic dyes. Combined with the QD photoluminescence quantum yield approaching 100% and their rock-solid photostability, this fact opens great prospects for the two-photon functional tumor imaging with QDs tagged with highly specific recognition molecules. Single-domain antibodies (sdAbs) or “nanobodies” derived from lamas are the smallest high-affinity recognition molecules, which may be tagged with the QDs thus permitting not only solid tumors multiphoton imaging but also rare disseminated cancer cells and micrometastases in the depth of the tissue to be detected.

Producing active polymer optical fibers (POFs) is a key step towards new applications such as fluorescent fiber solar concentrators (FFSCs), sensors, contactless coupling devices, or fiber integrated light sources and lasers. Therefore, integration of fluorescent nanoparticles into the polymer matrix is necessary and becomes accessible via in situ polymerization. For optical applications, the polymer has to fulfill various requirements such as chemical and physical stability, optical transparency in the application-relevant spectral region as well as a good synthetic accessibility. A common material for these is poly(methyl methacrylate) (PMMA). The β-phase NaYF₄:Yb³⁺,Er³⁺ upconversion nanoparticles (UCNP) were synthesized from the rare earth salts via thermal decomposition method in high-boiling point solvent 1-octadecene and capping agent oleic acid. Current results show hazy samples of the polymer with integrated nanoparticles made from monomer solution of methyl methacrylate. However, further optical tuning such as increasing the transparency of the bulk samples by changing the monomer solution to non-polar n-butyl methacrylate (nButMA) or cyclohexyl methacrylate (CHMA) or further optimization of the UCNP shell could lead to more suitable polymer bulk samples.

The interaction of semiconductor quantum dots CdZnSe/ZnS (QDs) and gold nanoparticles (Au NPs) in colloidal solutions was investigated. The replacement of ligands on the Au NP surface by mercaptocarboxylic acid molecules is shown to produce stable complexes of bound Au NPs and hydrophobic QDs with surface purified of organic ligands.

Local fields of metal nanoparticles can change quantum dots (QDs) absorption and luminescence. In this work, we have investigated the interaction of granulated Ag NPs films with CdSe/ZnS semiconductor QDs in hybrid structure with a-C:H thin films. We have studied hybrid structure with two a-C:H films on a quartz substrate having wider optical gap of 2.1 eV and narrow gap of 0.7 eV. The distribution of Ag NPs on the a-C:H was more ordered unlike a pure quartz surface. Homogeneous films of Ag NPs on a-C:H surface have narrower picks of LSPR in spectra. The intensity magnifying and the blue shift of the LSPR peak of Ag NPs on 31 nm in the spectra has been observed with an increase in the optical gap of a-C:H film. We have also compared how the properties of a-C:H films in hybrid structures with Ag NPs affect the absorption and luminescence of CdSe/ZnS quantum dots. The absorption maximum for the QDs on Ag NPs/a-C:H surface was higher than on Ag NPs on pure quartz. The red shift of the absorption peak was observed. We have observed photoluminescence quenching of the CdSe/ZnS QDs on the surfaces of the studied hybrid structures. The greatest quenching of QD luminescence was observed on quartz substrate. A less significant quenching of the CdSe/ZnS QDs luminescence was obtained in the sample with a-C:H film having a wider optical gap.

The techniques of preparation of layers of Cu_2 – xSe semiconductor plasmonic nanocrystals (SPNC) with plasmonic resonances in near infrared region from toluene colloidal solution are described. It is shown that combining QDs with SPNC layers lead to the enhancement of optical response from the QDs. The PVA film makes it possible to optimize the QDs-SPNC interlayer distance and provide most efficient enhancement.

The principle of operation of near-infrared LEDs based on PbS nanocrystals and aspects of their development are considered. The aging of nanocrystals with different ligand shells is analyzed, as well as spectral transmission of the bottom LED layers. Samples of light-emitting diodes based on NC are demonstrated, their electrical and optical parameters are studied. The emission at a wavelength of 1480 nm is demonstrated.

At present, fluorescent spectroscopy is a powerful tool that is used in many biology applications. In practice, fluorescent labels based on organic dyes and semiconductor quantum dots are used. It is noteworthy that the semiconductor quantum dots have distinct advantages over organic dyes. At the same time, the efficiency parameters and modes of detection and excitation have not been investigated sufficiently. The results of theoretical study on the optimization of the excitation and detections modes for detecting ultra-small amounts of CdSe/ZnS core/shell semiconductor quantum dots are presented at this paper.

The effect of temperature on luminescence of semiconductor nanocrystals is used for monitoring local heating of specimens studied at laser scanning microscope. The spectral position of luminescence maximum is a convenient parameter to be followed; its thermal shift remains nearly linear within a broad temperature range. Nanoplatelets are found advantageous nanosized temperature sensors as compared to quantum dots due to narrower luminescence spectrum.

We prepared thin films containing colloidal quantum dots CdSe/ZnS of four different mean core sizes, with photoluminescence maximum in the range 530–610 nm, and covered by different ligands, on the surface of water by the Langmuir method. We obtained Surface pressure–Area curves (π–A isotherms) of the formed films at room temperature under different conditions: the compression speed and the waiting time before the film was compressed. In the course of the studies, we established that the type of ligand that passivates the surface of the quantum dots greatly influences the formation of CdSe/ZnS Langmuir films, and that the compression speed and the waiting time before the film is compressed do not seriously affect the formation of the films.

The possibility of astigmatism compensation in a wide wavelength range in normal incidence schemes based on a spherical diffraction grating with variable groove density has been considered. Two schemes imaging spectrographs with dimensions of about 1 and 5 m for the wavelength ranges 820–1690 and 980–1520 Å that operate in the first external and first internal diffraction orders, respectively, have been calculated. It has been shown that the advantage of the external order of diffraction is a wide (more than an octave) spectral range at relatively compact sizes of the device. Schemes operating in internal orders of diffraction have better imaging characteristics, but large dimensions of the device are required to maintain the width of the wavelength range at the octave level. A comparison of the above schemes with schemes based on gratings with curvilinear grooves has been carried out. It has been shown that the variable line-spaced gratings yield a gain in the limiting spatial resolution, while the gratings with curvilinear grooves allow the achievement of a better limiting spectral resolution. The schemes of the considered type can be applied in the soft X-ray range when using diffraction gratings with a multilayer coating.

Optical transport parameters (transport propagation length of radiation and scattering length) have been experimentally studied in samples of a foamed liquid for a wavelength range of 500–900 nm. On the basis of the obtained experimental data, the values of the anisotropy parameter of light scattering in a foamed liquid are found as a function of the aging time. It is concluded that the values of the scattering anisotropy parameter close to zero in the early stages of aging are due to a strong correlation of the spatial positions of the scattering centers (gas bubbles in the liquid-phase matrix). The increase in the scattering anisotropy parameter with aging of the foam is due to “optical” inversion (a transition from the regime of light scattering by gas bubbles in a liquid to scattering by regions of intersections of the foam cell boundaries in a gas matrix medium).

The possibility of detecting the formation of immune complexes with the use of antibodies labeled with colloidal gold nanoparticles and optical spectroscopy is considered. Changes in the spectral characteristics of sols of gold nanoparticles with diameters of 15, 60, and 90 nm conjugated with immunoglobulins in the presence of especially dangerous infectious agents are recorded and analyzed. The data obtained indicate that the developed methodological approach to optical detection of immune complexes may be promising for creating immunochemical methods of identification of infectious agents.