Properties of Halide Perovskite Photodetectors with Little Rubidium Incorporation

This study investigates the effects of Rb doping on the Rb-formamidinium-methylammonium-PbI3 based perovskite photodetectors. Rb was incorporated in the perovskite films with different contents, and the corresponding photo-response properties were studied. Doping of few Rb (~2.5%) was found to greatly increase the grain size and the absorbance of the perovskite. However, when the Rb content was greater than 2.5%, clustering of the Rb-rich phases emerged, the band gap decreased, and additional absorption band edge was found. The excess Rb-rich phases were the main cause that degraded the performance of the photodetectors. By space charge limit current analyses, the Rb was found to passivate the defects in the perovskite, lowering the leakage current and reducing the trap densities of carriers. This fact was used to explain the increase in the detectivity. To clarify the effect of Rb, the photovoltaic properties were measured. Similarly, h perovskite with 2.5% Rb doping increased the short-circuit current, revealing the decline of the internal defects. The 2.5% Rb doped photodetector showed the best performance with responsivity of 0.28 AW−1 and ~50% quantum efficiency. Detectivity as high as 4.6 × 1011 Jones was obtained, owing to the improved crystallinity and reduced defects.

Modifications of EHPDB Physical Properties through Doping with Fe2O3 Nanoparticles (Part II)

The aim of our study was to analyze the influence of various concentrations of γ-Fe2O3 nanoparticles on the physical properties of the liquid crystalline ferroelectric SmC* phase, as well as to check the effect of introducing nanoparticles in the LC matrix on their properties in the prepared five nanocomposites. UV-vis spectroscopy showed that the admixture reduced the absorption of nanocomposites in the UV range, additional absorption bands appeared, and all nanocomposites were transparent in the range of 500–850 nm. The molecular dynamics in particular phases of the nanocomposites were investigated by the dielectric spectroscopy method, and it was found that nanoparticles caused a significant increase in the dielectric constant at low frequencies, a strong modification of the dielectric processes in the SmC* phase, and the emergence of new relaxation processes for the highest dopant concentrations. SQUID magnetometry allowed us to determine the magnetic nature of the nanoparticles used, and to show that the blocked state of nanoparticles was preserved in nanocomposites (hysteresis loops were also registered in the ferroelectric SmC* phase). The dependence of the coercive field on the admixture concentration and the widening of the hysteresis loop in nanocomposites in relation to pure nanoparticles were also found. In turn, the FT-MIR spectroscopy method was used to check the influence of the impurity concentration on the formation/disappearance or modification of the absorption bands, and the modification of both the FWHM and the maximum positions for the four selected vibrations in the MIR range, as well as the discontinuous behavior of these parameters at the phase transitions, were found.

Terahertz Spectral Properties of 5-Substituted Uracils

Applications of terahertz time-domain spectroscopy (THz-TDS) in the fields of chemistry and biomedicine have recently received increased attention. Specifically, THz-TDS is particularly effective for the identification of alkaloid molecules, because it can distinguish the vibration types of base molecules in the THz band and provide a direct characteristic spectrum for the configuration and conformation of biomolecules. However, when THz-TDS technology is used to identify alkaloid molecules, most of them are concentrated in the 0.1–3.0 THz band, limiting the amount of information that can be obtained. In this work, a wide-spectrum THz-TDS system was independently built to explore the absorption spectra of uracil and its 5-substituents in the range of 1.3–6.0 THz. We found that, in the THz band, uracil and its 5-substituents have similar absorption peaks near 4.9 and 3.3 THz, while the 5-substituents have an additional absorption peak in the range of 1.5–2.5 THz. This absorption peak is red-shifted as the relative atomic mass of the 5-substituted atoms increases. Gaussian software was adopted to calculate the absorption spectra of the samples. The simulation conclusions were in good agreement with the experimental results, revealing that the vibration of the base molecule at low frequencies can be attributed to the inter-molecular vibration. This work demonstrates that THz-TDS technology can be used to accurately identify biomolecules with similar molecular structures, reflecting the importance of molecular structure in biological activity.

Synthesis of gold nanoparticles by the spark discharge method for visible plasmonics

This work demonstrates synthesis of metal Au nanoparticles with a plasmon resonance in the visible optical region by the spark discharge method in atmosphere of argon of purity 6.0. With raising of sintering temperature from 25 to 950 °C, the morphology of synthesized Au nanoparticles changed from agglomerates to individual particles with decreasing the median size from 270 to 90 nm according to aerosol spectrometer. While by transmission electron microscopy primary nanoparticles with a gold crystalline structure with sizes in range from 5 to 120 nm were observed. Synthesized nanoparticles ensembles had broad absorption peaks with maximum in the visible optical region with peak positions approximately at 490 nm. High temperature sintered particles had a spherical shape and an additional absorption peak at approximately 640 nm.

Ultrawideband electromagnetic metamaterial absorber utilizing coherent absorptions and surface plasmon polaritons based on double layer carbon metapatterns

An ultrawideband electromagnetic metamaterial absorber is proposed that consists of double-layer metapatterns optimally designed by the genetic algorithm and printed using carbon paste. By setting the sheet resistance of the intermediate carbon metapattern to a half of that of the top one, it is possible to find an optimal intermediate metapattern that reflects and absorbs the EM wave simultaneously. By adding an absorption resonance via a constructive interference at the top metapattern induced by the reflection from the intermediate one, an ultrawideband absorption can be achieved without increasing the number of layers. Moreover, it is found that the metapatterns support the surface plasmon polaritons which can supply an additional absorption resonance as well as boost the absorption in a broad bandwidth. Based on the simulation, the $$90\%$$ 90 % absorption bandwidth is confirmed from 6.3 to 30.1 GHz of which the fractional bandwidth is 130.77$$\%$$ % for the normal incidence. The accuracy is verified via measurements well matched with the simulations. The proposed metamaterial absorber could not only break though the conventional concept that the number of layers should be increased to extend the bandwidth but also provide a powerful solution to realize a low-profile, lightweight, and low cost electromagnetic absorber.

Ultrafast Dynamics of Optical Nonlinearities in β-Ga2O3

We report the different nonlinear optical mechanisms and defect-related carrier dynamics in Sn-doped β-Ga2O3 crystal by utilizing time-resolved pump-probe technique based on phase object under UV excitation. The obtained nonlinear optical parameters arise from bound electron can be well explained by the theoretical calculation of two-band model and Kramers-Kronig transformation. By tuning the probe wavelength, the carrier nonlinearity can be modulated greatly due to additional absorption of defects within the bandgap. The results reveal that by choosing a proper probe wavelength that matches the defect state to the valence band, the nonlinear absorption and refraction of the carriers can be greatly enhanced, which provides an important reference for the design of gallium oxide-based waveguide materials and all-optical switching materials in the future.

Electromagnetic Properties and Microwave Absorption of Electrospun Fe2O3-Carbon Composite Nanofibers with Particle–Nanorod Structure

Multifunctional composite nanostructure prepared via electrospinning has attracted wide attention. In this study, Fe2O3-carbon composite nanofiber with particle–nanorod structure was successfully prepared via electrospinning and followed calcination. Then, the electromagnetic properties of this material have been fully characterized, and the influence of different preparation conditions on these properties has been studied. In addition, compared to pure [Formula: see text]-Fe2O3 nanoparticles and hollow Fe2O3 nanofibers, the composite nanofibers with a thickness of 2.64[Formula: see text]mm exhibited an additional absorption peak at a frequency of 13.92[Formula: see text]GHz and an enhancement in absorption at a frequency of 15.45[Formula: see text]GHz, which may be attributed to the increase in electrical loss introduced by amorphous carbon and the enhanced magnetic loss resulting from the multi-stage reflection introduced by the particle–nanorod structure. This study shows that the composite of Fe2O3 and carbon, and the introduction of the particle–nanorod structure can improve the microwave absorption efficiency of materials, and more nanocomposites can be designed like this to further improve their electromagnetic properties and absorption efficiency in the future.

INCREASING THE EFFICIENCY OF THE SYSTEMS OF COMPRESSOR-PUMPING AND REFRIGERATION UNITS SUPPLYING LIQUID CO2 AND NH3 TO THE UNIT FOR CARBAMIDE SYNTHESIS

Carbon dioxide is used in large volumes to produce urea, a highly efficient nitrogen fertilizer. It is compressed in a multistage compressor to a pressure of 15 MPa and fed to the urea synthesis unit. The specific energy consumption for the compression of carbon dioxide by a compressor reaches 0.16 kWh/kg. It may be more profitable to use in the system of compressor-pumping and refrigeration units. They can be used to liquefy carbon dioxide and compress it to pressure 15 MPa before feeding it to the synthesis of urea. In the simplest scheme, an ammonia compression refrigeration machine (ACRM) is included in the system to improve efficiency. The specific energy consumption in such a system for the liquefaction and compression of CO2 is 0.118 kWh/kg. In case of replacement of the ACRM with an absorption refrigeration machine, unit costs can be reduced to 0.09 kWh/kg. These two systems can be used to increase urea production or to ensure stable operation of the units during the summer period of their operation. The analysis showed that further improvement of the technological scheme of the entire system will completely abandon the use of the compressor method of compression of CO2 to pressure 15 MPa before its supply to the urea synthesis unit. To do this, you need to include an additional absorption lithium bromide refrigeration machine in the system. In this scheme, the compressor-pumping unit will provide the simultaneous supply of liquid carbon dioxide and ammonia for the synthesis of urea with a pressure of 15 MPa. To increase the daily production of urea from 1400 to 2000 tons, it is necessary to increase the feed liquid CO2 in the amount of 62 t/hour and liquid NH3 — 47.5 t/hour. Bibl. 14, Fig. 3.

Optical absorption of LiNaGe4O9:Mn crystal

The paper reports the results of optical absorption spectra studying in LiNaGe4O9 crystal doped with Mn. It is shown that Mn impurity causes the appearance of the additional absorption bands. The intensities of these bands change in different ways in the range of the ferroelectric phase transition. Semi-empirical version of the crystal field theory is used to discuss localization and charge state of Mn impurity ions in the LiNaGe4O9 structure.

Unusual optical centres in fancy brown diamonds

Background. Natural brown diamonds with fancy yellow, orange, red and green tints are valuable jewelry raw materials. Their colour is associated with post-crystallisation plastic deformation occurring during transportation from the mantle to the Earth’s surface.Aim. To study point defects in plastically deformed diamonds using optical and IR spectroscopy.Materials and methods. Faceted brown diamonds with fancy tints presented on the Russian market were studied spectroscopically. Selected samples were examined using UV-visible optical absorption spectroscopy and IR spectroscopy.Results. We discovered unusual optical centres in the absorption spectra of the UV-visible region. In addition, the known continuous absorption increasing from the red to the ultraviolet region of the spectrum, as well as the N3 and H3 nitrogen centres and a band at 550 nm, were revealed. In the spectra of yellowish-brown diamonds, the bands at 512.9 nm and 519.9 nm and an accompanying broad band with a maximum of 480 nm were found. The appearance of a yellowish tint of crystals was associated with these optical centres. The bands 506.5 nm, 516.1 nm and 679.7 nm were established in the spectrum of orange-brown diamond samples. An additional absorption continuum associated with single nitrogen atoms and centres (NV)– were observed in greenish-brown diamond samples. Their simultaneous presence causes the appearance of a greenish tint in the diamond colour.Conclusion. The information obtained using IR spectroscopy indicates that an intense brown colour can occur not only in the most common Ia type crystals according to the physical classification of diamonds, but also in relatively rare Ib + IaA type diamonds.