Spectral optical properties of synthesized ceramic nanoporous membranes based on anodic aluminum oxide coated silver in saturated ammonia gas flow have been experimentally investigated. Based on the measured transmission spectra and detected interference part of the spectra in wavelength range from 550 to 900 nm, temporal and spectral dependencies of the effective optical thickness and its changes in non-equilibrium conditions were obtained due to adsorption of ammonia molecules on silver film surface. According to detected and measured interference maximum shifts up to 14 nm in transmission spectra of Al2O3 + Ag membranes in ammonia gas flow, the possibility of constructing a selective interferometric optical sensors with 10-15 min response time is shown. Keywords: porous anodic aluminium oxide, membrane, silver film, light interference, ammonia vapors, effective optical thickness, interference maximum shift.

Various approaches to the optical diagnostics of evolving polymer foams formed as a result of a decrease in the external pressure according to a given scenario in the "polymer-supercritical fluid" systems are considered.Formed polymer foams are considered as a material platform for the creation of scaffolds for biomedical applications. Diagnostics of the current state of the foam was carried out by statistical analysis of the spatiotemporal fluctuations of the probe laser radiation,multiple scattered in the volume of the evolving foam, or by analyzing the fluorescent response during foaming of the "polymer-fluorophore" mixture, pumped by laser radiation in the absorption band of the fluorophore. A relationship has been established between the average lifetime of dynamic speckles in scattered laser light and a generalized parameter characterizing the foam expansion dynamics. It was also found that the waveguide effect in the walls of the formed pores has a significant influence on the fluorescent response of the evolving foam, leading to an increase in the characteristic dwell time of fluorescence radiation in the walls and, accordingly, to an increase in the contribution of the induced component to the fluorescent response. Keywords: fluorescent response, speckle correlometry, polylactide, foaming, supercritical carbon dioxide.

Experimental data on the narrowing of fluorescence spectra of laser-pumped random media are interpreted within the framework of a probabilistic model of incoherent amplification of the stimulated component of fluorescence. R6G- and DCM-doped layers of dense-packed anatase and anatase-rutile particles and suspensions of DCM crystallites were examined under pulse-periodic laser pumping with various pump intensities at the wavelength of 532 nm. It was shown that, in the case of quasi-stationary fluorescence response at high pump intensities, amplification of stochastically propagating partial components of fluorescence field at various wavelengths is governed by the pump-independent factor of fluorescence amplification and the average number of stimulated emission acts in the pumped system. Analysis of the experimental data has shown that, despite certain simplifying assumptions, the considered model reasonably describes evolution of the fluorescence spectra of random fluorescent media with the increase in the pump intensity. A procedure of recovery of the fluorescence amplification factor from the sets of fluorescence spectra obtained at various pump intensities is considered. Features of the spectral shapes of the recovered amplification factors caused by the influence of the scattering matrices in pumped media are discussed.

A comprehensive study was performed on the supramolecular ordering and optical properties of thin nanostructured glycerohydrogel sol-gel plates based on chitosan L- and D-aspartate and their individual components in the X-ray, UV, visible, and IR ranges. Our comparative analysis of chiroptical characteristics, optical collimated transmittance, the average cosine of the scattering angle, microrelief and surface asymmetry, and the level of structuring shows a significant influence of the wavelength range of electromagnetic radiation and the enantiomeric form of aspartic acid on the functional characteristics of the sol-gel materials. At the macrolevel of the supramolecular organization, a complex topography of the surface layer and a dense amorphous–crystalline ordering of polymeric substances were revealed, while at the nanolevel, there were two forms of voluminous scattering domains: nanospheres with diameters of 60–120 nm (L-) and 45–55 nm (D-), anisometric particles of lengths within ~100–160 (L-) and ~85–125 nm (D-), and widths within ~10–20 (L-) and ~20–30 nm (D-). The effect of optical clearing on glass coated with a thin layer of chitosan L-(D-)aspartate in the near-UV region was discovered (observed for the first time for chitosan-based materials). The resulting nanocomposite shape-stable glycerohydrogels seem promising for sensorics and photonics.

Background and Objectives: Electrically conductive layers of densely packed semiconductor nanoparticles are a promising material platform for creating, in particular, multisensor chemoresistive systems. A significant disadvantage of multielement chemoresistive sensors of this type is the long-term instability of the parameters of individual elements and large values of response and relaxation times to the initial state. Such a process can be considered as a transition “semiconductor – insulator” in dispersed disordered systems, and the dynamics of the transition can be described in the framework of the percolation theory. The aim of this work was experimental studies and statistical modeling of the effect of degradation of ohmic conductivity of low-dimensional layers of densely packed indium oxide (In2O3) nanoparticles under long-term DC current flow. Dispersed nanostructured layers of indium oxide were chosen as an object of study due to the specific electrophysical properties of this indirect-gap n-type semiconductor. Materials and Methods: Experimental studies of the effect of degradation of ohmic conductivity of dispersed semiconductor structures under long-term exposure to direct current were carried out using specially prepared samples consisting of densely packed indium oxide nanoparticles (In2O3). The effect of structure thickness on the percolation threshold as well as the critical index of the conductivity function was numerically investigated. A cubic resistor network was considered for numerical analysis of the conductivity of a two-phase percolation structure. The network was uniformly and randomly filled with conducting and insulating nodes. Results: One of the main observed features of electron transfer in bridge disordered ensembles of nanoparticles of the studied systems is the achievement of percolation threshold at long-term exposure to direct current and extremely low rate of recovery of deteriorated conductivity after removal of exposure. The established value of the critical conductivity index for the studied structures has an intermediate value between theoretical estimates for three-dimensional and two-dimensional percolation systems, which allows us to consider the studied structures as transitional between two-dimensional and three-dimensional systems. Conclusion: The obtained results can be used as a physical basis for the development of new approaches to the creation of thin structures with limited conductivity.

The results of experimental studies of the effect of degradation of macroscopic charge transport in ensembles of close-packed anatase nanoparticles under long-term action of a constant electric field are presented. The degradation is presumably due to the increasing degree of blocking of statistically independent conduction channels formed in ensembles of particles under the field action. A phenomenological model is considered for estimating the number of active conduction channels in an ensemble of particles near the percolation threshold in the system. Keywords: nanoparticles, anatase, charge transfer, percolation threshold.

The results of experimental studies of the effect of degradation of macroscopic charge transport in ensembles of close-packed anatase nanoparticles under long-term action of a constant electric field are presented. The degradation is presumably due to the increasing degree of blocking of statistically independent conduction channels formed in ensembles of particles under the field action. A phenomenological model is considered for estimating the number of active conduction channels in an ensemble of particles near the percolation threshold in the system.

The results of experimental studies of ohmic conductivity degradation in the ensembles of nanostructured anatase bridges under a long-term effect of direct current are presented. Stochastic sets of partially conducting inter-electrode bridges consisting of close-packed anatase nanoparticles were formed by means of the seeding particles from drying aqueous suspensions on the surfaces of silica substrates with interdigital platinum electrodes. Multiple-run experiments conducted at room temperature have shown that ohmic conductivity degradation in these systems is irreversible. It is presumably due to the accumulated capture of conduction electrons by deep traps in anatase nanoparticles. The scaling analysis of voltage drops across the samples at the final stage of degradation gives a critical exponent for ohmic conductivity as ≈1.597. This value satisfactorily agrees with the reported model data for percolation systems. At an early stage of degradation, the spectral density of conduction current fluctuations observed within the frequency range of 0.01–1 Hz decreases approximately as 1/ω, while near the percolation threshold, the decreasing trend changes to ≈1/ω2. This transition is interpreted in terms of the increasing contribution of blockages and subsequent avalanche-like breakdowns of part of the local conduction channels in the bridges into electron transport near the percolation threshold.

We consider an on-chip sensor array based on a mesoporous layer of SnO2 nanoparticles to be screen printed on the multielectrode-supplied Si/SiO2 substrate as a chemiresistive building platform for portable and personalized in situ instruments. To differentiate the local oxide layer properties we apply Nd:YAG laser whose scanning etched various layer areas at varied power driven by working current in 24.8 A-26.7 A range. As a result, the SnO2 layer has dual-grad modified properties as, (i) a spatial modification of thickness down to nm-range, and (ii) the change of oxidation state with appearance of traces of SnO, which both result in a great varying of gas -sensing properties of local sensor elements over the array. To test the functionality of the chip, we could detect vapors of four ketones (acetone, cyclopentanone, cyclohexanone, 2-octanone) and four alcohols (methanol, ethanol, isopropanol, butanol), at sub-, down to ca. 100 ppb, and low, up to 10, ppm concentrations with their selective recognition via processing the array's vector signal by linear discriminant algorithm. Primarily, we show differences in the interaction of ketones and alcohols with SnO2 surface by first-principle calculations in frames of density functional theory to serve as fundamental receptor pre-requisites for the analyte's selective discrimination by the oxide layer under the multisensor concept to employ here. We consistently show that two modes of the sensor operation could be rather equally applied to the array as, (i) UV LED, 366 nm wavelength, irradiation at room temperature, and (ii) heating up to approx. 583 K. While the heating provides faster and higher chemiresistive responses, the UV-excited mode provides more selective vector signals, lower energy consumption, and a higher signal-to-noise ratio.

Various approaches to the optical diagnostics of evolving polymer foams formed as a result of a decrease in the external pressure according to a given scenario in the "polymer - supercritical fluid" systems are considered.Formed polymer foams are considered as a material platform for the creation of scaffolds for biomedical applications. Diagnostics of the current state of the foam was carried out by statistical analysis of the spatiotemporal fluctuations of the probe laser radiation,multiple scattered in the volume of the evolving foam, or by analyzing the fluorescent response during foaming of the "polymer-fluorophore" mixture, pumped by laser radiation in the absorption band of the fluorophore. A relationship has been established between the average lifetime of dynamic speckles in scattered laser light and a generalized parameter characterizing the foam expansion dynamics. It was also found that the waveguide effect in the walls of the formed pores has a significant influence on the fluorescent response of the evolving foam, leading to an increase in the characteristic dwell time of fluorescence radiation in the walls and, accordingly, to an increase in the contribution of the induced component to the fluorescent response.

The results of experimental studies of the fluorescence response of polylactide foams saturated with rhodamine 6G and composites used for their preparation in the region of transition from spontaneous fluorescence to stochastic laser generation are presented. A small increase in the threshold of stochastic laser generation in foamed composites compared to the expected one is interpreted as a result of the contribution of the waveguide mode of fluorescence propagation in the polymer matrix.. Keywords: polylactide foam, spontaneous fluorescence, stochastic laser generation, waveguide mode.

The saturation of the spectral quality of the fluorescence response of randomly inhomogeneous media to external laser pump with intensities above the random lasing threshold in a medium has been studied. It has been found that the saturation of the fluorescence spectral quality is due to a decrease in the fluorescence enhancement length in the medium to the minimum value determined by the average size of local fluorescence emitters associated with laser speckles and by radiative exchange between emitters.

Spectral optical properties of synthesized ceramic nanoporous membranes based on anodic aluminum oxide coated silver in saturated ammonia gas flow have been experimentally investigated. Based on the measured transmission spectra and detected interference part of the spectra in wavelength range from 550 to 900 nm, temporal and spectral dependencies of the effective optical thickness and its changes in non-equilibrium conditions were obtained due to adsorption of ammonia molecules on silver film surface. According to detected and measured interference maximum shifts up to 14 nm in transmission spectra of Al2O3 + Ag membranes in ammonia gas flow, the possibility of constructing a selective interferometric optical sensors with 10 − 15 min response time is shown.

The results of experimental studies of the fluorescence response of polylactide foams saturated with rhodamine 6G and composites used for their preparation in the region of transition from spontaneous fluorescence to stochastic laser generation are presented. A small increase in the threshold of stochastic laser generation in foamed composites compared to the expected one is interpreted as a result of the contribution of the waveguide mode of fluorescence propagation in the polymer matrix.

A fundamental limitation of the spectral response of laser-pumped fluorescent nanostructured media was considered in terms of a probabilistic model establishing the relationship between the enhancement factor of a spectral quality and characteristic propagation and amplification scales of pump light and fluorescence in the medium. It was shown that the minimum spectral width of fluorescent response of the pumped medium is limited by competition between the stimulated emission and radiation losses in microscopic fluorescence emitters associated with the speckles randomly modulating the pumping light field. Theoretical results were compared to the experimental data on the spectral properties of the fluorescent response of laser-pumped nanostructured "anatase nanoparticles-dye solutions" systems with various structural and optical properties. Rhodamine 6G and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) were applied as fluorescent components in the examined systems with various scatter volume fractions, which were pumped by pulse-periodic laser radiation with various intensities at 532 nm. Comparison showed a fair agreement between the theoretical and experimental results.

Photo-conductance of quasi-2D layers of molybdenum disilicide nanoparticles was studied under pulse-periodic laser pumping in the spectral range from 355 nm to 480 nm. The layers were prepared using deposition of the nanoparticles from the water suspensions onto the interdigital electrode systems. The influence of the temperature on the photoconductance is examined.

Microscopic structural rearrangements in expanding polylactide foams were probed using multiple dynamic scattering of laser radiation in the foam volume. Formation and subsequent expansion of polylactide foams was provided by a rapid or slow depressurization of the “plasticized polylactide–supercritical carbon dioxide” system. Dynamic speckles induced by a multiple scattering of laser radiation in the expanding foam were analyzed using the stacked speckle history technique, which is based on a joint mapping of spatial–temporal dynamics of evolving speckle patterns. A significant decrease in the depressurization rate in the case of transition from a rapid to slow foaming (from 0.03 MPa/s to 0.006 MPa/s) causes dramatic changes in the texture of the synthesized stacked speckle history maps. These changes are associated with transition from the boiling dynamics of time-varying speckles to their pronounced translational motions and are manifested as significant slopes of individual speckle traces on the recovered stacked speckle history maps. This feature is interpreted in terms of the actual absence of a new cell nucleation effect in the expanding foam upon slow depressurization on the dynamic scattering of laser radiation.

Numerical model for calculations of spatio-temporal variations of amplitudes of counter-propagating pulses in a standing-wave laser cavity is proposed. Proposed model is based on the transport-type equations for the envelopes of oppositely running pulses, spatial discretization along the cavity axis, and calculation of temporal variations both electric field amplitude and active media polarization/inversion at these points.