New Publications

Glass crystallization making red phosphor for high-power warm white lighting

Hu, Tao; Ning, Lixin; Gao, Yan; Qiao, Jianwei; Song, Enhai; et al. Light-science & Applications. DOI https://doi.org/10.1038/s41377-021-00498-6

Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence, and especially relies on blue light pumped red phosphors for improved light quality. Herein, we discovered an unprecedented red-emitting Mg2Al4Si5O18:Eu2+ composite phosphor (λex = 450 nm, λem = 620 nm) via the crystallization of MgO–Al2O3–SiO2 aluminosilicate glass. Combined experimental measurement and first-principles calculations verify that Eu2+ dopants insert at the vacant channel of Mg2Al4Si5O18 crystal with six-fold coordination responsible for the peculiar red emission. Importantly, the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%, and stable emission against thermal quenching, which reaches industry production. The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 lm and 54 lm W−1, respectively. The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate, that the Mg2Al4Si5O18:Eu2+ composite phosphor will provide a significant step towards the development of high-power solid-state lighting.

DOI: https://doi.org/10.1038/s41377-021-00498-6

Polymer Dispersed Cholesteric Liquid Crystals with a Toroidal Director Configuration under an Electric Field

Gardymova, Anna P.; Krakhalev, Mikhail N.; Zyryanov, Victor Ya.; Gruzdenko, Alexandra A.; Alekseev, Andrey A.; et al. Polymers. https://doi.org/10.3390/polym13050732

The electro-optical properties of polymer dispersed liquid crystal (PDLC) films are highly dependent on the features of the contained liquid crystal (LC) droplets. Cholesteric LC droplets with homeotropic boundaries can form several topologically different orientational structures, including ones with single and more point defects, layer-like, and axisymmetric twisted toroidal structures. These structures are very sensitive to an applied electric field. In this work, we have demonstrated experimentally and by computer simulations that twisted toroidal droplets reveal strong structural response to the electric field. In turn, this leads to vivid changes in the optical texture in crossed polarizers. The response of droplets of different sizes were found to be equivalent in terms of dimensionless parameters. In addition, the explanation of this phenomenon showed a comparison of theoretical and experimental structural response curves aids to determine the shape of the droplet. Finally, we demonstrated that the addition of a dichroic dye allows such films to be used as optical filters with adjustable color even without polarizers. 

https://doi.org/10.3390/polym13050732

Magnetization reversal and sign reversal exchange bias field in polycrystalline Ni5.33Ta0.67B2O10

Sofronova, S. N.; Kazak, N., V; Eremin, E., V; Moshkina, E. M.; Chernyshov, A., V; et al. Journal Of Alloys And Compounds. https://doi.org/10.1016/j.jallcom.2020.158200

The sign reversal of both magnetization and exchange bias field was studied in the polycrystalline Ni5.33Ta0.67B2O10. The crystal structure of Ni5.33Ta0.67B2O10 is quasi–low dimensional due to NiO6/TaO6 octahedra forming two dimensional infinite layers. The antiferromagnetic/ferrimagnetic phase transition was observed at TN = 165 K. The negative exchange bias effect was found in the 30–90 K temperature range, whereas the positive exchange bias effect was observed at temperatures below 30 K. We assume that the exchange bias effect is due to different types of magnetic ordering of Ni2+ magnetic moments in two layers.

https://doi.org/10.1016/j.jallcom.2020.158200

Optical and Magnetic Properties of the DyxCo1-x/Bi/Py Trilayers

Kosyrev, N. N.; Yakovchuk, V. Yu; Patrin, G. S.; Komarov, V. A.; Volchenko, E. N.; et al. Technical Physics Letters. DOI https://doi.org/10.1134/S1063785021020097

We report on the results of investigations of the optical and magnetooptical properties of DyxCo1 – x/Bi/Py (Py is permalloy) trilayers. The temperature dependence of the magnetization has been examined using the magnetooptical Kerr effect and the optical refractive and absorption indices have been measured by spectral ellipsometry. It is shown that the thickness of the bismuth spacer affects the exchange coupling between the permalloy and DyCo layers, which manifests itself in the change in the magnetization compensation temperature and in the character of the exchange coupling.

DOIhttps://doi.org/10.1134/S1063785021020097

Biogenic Ferrihydrite Nanoparticles: Synthesis, Properties In Vitro and In Vivo Testing and the Concentration Effect

Stolyar, Sergey V.; Kolenchukova, Oksana A.; Boldyreva, Anna V.; Kudryasheva, Nadezda S.; Gerasimova, Yulia V.; et al. Biomedicines. https://doi.org/10.3390/biomedicines9030323

Biogenic ferrihydrite nanoparticles were synthesized as a result of the cultivation of Klebsiella oxytoca microorganisms. The distribution of nanoparticles in the body of laboratory animals and the physical properties of the nanoparticles were studied. The synthesized ferrihydrite nanoparticles are superparamagnetic at room temperature, and the characteristic blocking temperature is 23–25 K. The uncompensated moment of ferrihydrite particles was determined to be approximately 200 Bohr magnetons. In vitro testing of different concentrations of ferrihydrite nanoparticles for the functional activity of neutrophilic granulocytes by the chemiluminescence method showed an increase in the release of primary oxygen radicals by blood phagocytes when exposed to a minimum concentration and a decrease in secondary radicals when exposed to a maximum concentration. In vivo testing of ferrihydrite nanoparticles on Wister rats showed that a suspension of ferrihydrite nanoparticles has chronic toxicity, since it causes morphological changes in organs, mainly in the spleen, which are characterized by the accumulation of hemosiderin nanoparticles (stained blue according to Perls). Ferrihydrite can also directly or indirectly stimulate the proliferation and intracellular regeneration of hepatocytes. The partial detection of Perls-positive cells in the liver and kidneys can be explained by the rapid elimination from organs and the high dispersion of the nanomaterial. Thus, it is necessary to carry out studies of these processes at the systemic level, since the introduction of nanoparticles into the body is characterized by adaptive-proliferative processes, accompanied by the development of cell dystrophy and tension of the phagocytic system. 

 https://doi.org/10.3390/biomedicines9030323

Co/multi-walled carbon nanotubes/polyethylene composites for microwave absorption: Tuning the effectiveness of electromagnetic shielding by varying the components ratio

Kazakova, Mariya A.; Semikolenova, Nina, V; Korovin, Evgeniy Yu; Zhuravlev, Viktor A.; Selyutin, Alexander G.; et al. Composites Science And Technology. https://doi.org/10.1016/j.compscitech.2021.108731

We present novel polyethylene (PE) composites for electromagnetic interference (EMI) shielding application. They are based on cobalt modified multi-walled carbon nanotubes (MWCNTs) produced via in situ polymerization of ethylene, with the Ti-Ziegler–Natta catalyst preliminarily immobilized on Co/MWCNT hybrids. The electromagnetic properties of the composites were tuned by varying the filler loading and Co:MWCNT ratio. The microstructure of the composites and electromagnetic absorption process were carefully characterized by transmission and scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, ferromagnetic resonance and vector network analysis. The electromagnetic wave absorbing properties of the nanocomposite were investigated in the 10 MHz−18 GHz frequency range revealing that the EMI absorption properties can be tuned by varying the Co:MWCNT weight ratio in the filler. Interestingly, the Co/MWCNT-PE composite with a total filler and Co loading of only 12 and 1.7 wt%, respectively, showed extremely high reflection loss (RL) of −55 dB. More importantly, an effective bandwidth of 12.8–17.8 GHz (RL below −10 dB) was achieved for a matching thickness of only 1.5 mm. The specific RL value (RL/filler loading) of the composite was superior in comparison with the previously reported nanostructured carbon materials. The highly effective absorbing properties of Co/MWCNT-PE composites are explained primarily by the unprecedented uniform filler distribution in the polyethylene as well as by the synergistic effect of MWCNTs and Co nanoparticles. This approach thus offered an effective strategy to design cost-effective, lightweight and flexible EMI shielding materials with tunable dielectric and magnetic performance.

https://doi.org/10.1016/j.compscitech.2021.108731

Quasi-Bound States in the Continuum with Temperature-Tunable Q Factors and Critical Coupling Point at Brewster's Angle

Bing‐Ru Wu Jhen‐Hong Yang Pavel S. Pankin Chih‐Hsiang Huang Wei Lee Dmitrii N. Maksimov Ivan V. Timofeev Kuo‐Ping Chen. Laser & Photonics Reviews https://doi.org/10.1002/lpor.202000290

Quasibound state in the continuum (quasi‐BIC) is a long‐lived state with a high quality factor (Q factor). Here quasi‐BICs in nematic liquid crystal (LC) layer embedded between a distributed Bragg reflector (DBR) and a metal layer are studied. First, a special class of true BICs between the DBR and the metal film with field localization provided by the Brewster transverse electric (TE) reflection in the DBR is experimentally demonstrated. It is demonstrated that the Q factor of the quasi‐BIC can be tuned by the LC optical axis rotation in a wide range being only restricted by metal losses. The change of coupling with the radiation channel leads to a critical coupling condition, providing a total absorption of incident light. The acquired quasi‐BIC resonance is extremely sensitive to the temperature due to the narrow nematic temperature range of the LC. The quasi‐BIC transforms to BIC at the LC‐isotropic clearing point, due to closing of the radiation channel.

https://doi.org/10.1002/lpor.202000290

State-of-art plasmonic photonic crystals based on self-assembled nanostructures

Yadav, Ashish; Yadav, Neha; Agrawal, Vikash; Polyutov, Sergey P.; Tsipotan, Alexey S.; et al. Journal Of Materials Chemistry C. DOI: 10.1039/D0TC05254J

Controlled self-assembly of plasmonic photonic nanostructures provides a cost-effective and efficient methodology to expand plasmonic photonic nano-platforms with unique, tunable, and coupled optical characteristics. Keeping advantages and challenges in view, this review highlights contemporary advancements towards the development of self-assembly of a plasmonic photonic nanostructure using a colloidal solution and a self-assembly modeling technique along with exploring novel optical properties and associated prospects. The potential applications of self-assembled plasmonic photonic nano-systems to investigate next-generation optoelectronic devices, the need to reduce and increase scaling up aspects, and improve the performance, are also covered briefly in the review. The need of considerable efforts for the design and development towards establishing novel cost-effective methods to fabricate controlled self-assembled smart nano-plasmonic platforms is also highlighted in this mini-review. Key confronting issues that precisely limit the self-assemblies of photonic nanostructures and desired integration with other device components, mainly including uniformity within miniaturized devices are also discussed. This review will serve as a guideline and platform to plan advanced research in developing self-assembled plasmonic photonic nano-systems to investigate smart functional optical devices.

Near zero thermal expansion in metal matrix composites based on intermediate valence systems: Al/SmB6

Serebrennikov, D. A.; Bykov, A. A.; Trigub, A. L.; Kolyshkin, N. A.; Freydman, A. L.; et al. Results In Physics. https://doi.org/10.1016/j.rinp.2021.103843

This work is focused on the fabrication and characterization of a new type of composite invar materials combining near-zero thermal expansion and functional properties that are important for applications. This is accomplished through the use of particles of SmB6, an intermediate valence system with negative thermal expansion, embedded in Al matrix. The composite based on SmB6-21 vol% was fabricated by hot pressing and was characterized by XRD, optical/electron microscopy, X-ray computed tomography and capacitive dilatometry. The study of thermal expansion revealed that the sample exhibits invar behaviour up to ~60 K with a zero value of the coefficient of thermal expansion near 45 K. In comparison to pure aluminum, the temperature range has increased by about 20 K. A quantitative analysis of dilatometric experimental data performed on the basis of widely used theoretical models showed that the thermal expansion of the Al/SmB6 composite was well reproduced within the Turner model.

Polymer Dispersed Cholesteric Liquid Crystals with a Toroidal Director Configuration under an Electric Field

Gardymova, Anna P.; Krakhalev, Mikhail N.; Zyryanov, Victor Ya.; Gruzdenko, Alexandra A.; Alekseev, Andrey A.; et al. Polymers. https://doi.org/10.3390/polym13050732

The electro-optical properties of polymer dispersed liquid crystal (PDLC) films are highly dependent on the features of the contained liquid crystal (LC) droplets. Cholesteric LC droplets with homeotropic boundaries can form several topologically different orientational structures, including ones with single and more point defects, layer-like, and axisymmetric twisted toroidal structures. These structures are very sensitive to an applied electric field. In this work, we have demonstrated experimentally and by computer simulations that twisted toroidal droplets reveal strong structural response to the electric field. In turn, this leads to vivid changes in the optical texture in crossed polarizers. The response of droplets of different sizes were found to be equivalent in terms of dimensionless parameters. In addition, the explanation of this phenomenon showed a comparison of theoretical and experimental structural response curves aids to determine the shape of the droplet. Finally, we demonstrated that the addition of a dichroic dye allows such films to be used as optical filters with adjustable color even without polarizers.

 https://doi.org/10.3390/polym13050732

Potential energy surfaces of adsorption and migration of transition metal atoms on nanoporus materials: The case of nanoporus bigraphene and G-C3N4

Melchakova, I (Melchakova, Iuliia)[ 1 ] ; Nikolaeva, KM (Nikolaeva, Kristina M.)[ 2 ] ; Kovaleva, EA (Kovaleva, Evgenia A.)[ 3 ] ; Tomilin, FN (Tomilin, Felix N.)[ 2,3,4 ] ; Ovchinnikov, SG (Ovchinnikov, Sergey G.)[ 2,4 ] ; Tchaikovskaya, ON (Tchaikovskaya, Olga N.)[ 3 ] ; Avramov, PV (Avramov, Pavel V.)[ 1 ] ; Kuzubov, AA (Kuzubov, Alexander A.)[ 2 ] APPLIED SURFACE SCIENCE DOI: 10.1016/j.apsusc.2020.148223

First-row transition metal (TM) atoms adsorption and migration on nanoporus 2D materials like bigraphene with double vacancies and g-C3N4 as the active sites for TM nanocluster's growth was studied within the framework of density functional theory. Both thermodynamic and kinetic aspects of composite synthesis were discussed. It was found that potential barriers of adatom's migration from bigraphene's outer surface to the interlayer space through the double vacancy are rather low values. High potential barriers of TM migration along the carbon plane prevents TM clusterization due to enhanced chemical activity of double vacancies which gives a possibility to capture the surface adatoms. As was shown for the monolayer graphene, the decrease of vacancies concentration reduces the barrier of adatom migration along the surface while the second graphene sheet in bigraphene stabilizes the structure. The behavior of TM-atom regarding g-CN2 and g-CN1 nanosheets was investigated. Potential energy surfaces were obtained and discussed. The migration barriers were found surmountable that means high probability of migration of TM adatoms to global minima and formation of TM vacancies. Comparison of barriers values with Boltzmann factor demonstrated that just standalone temperature fluctuations cannot initiate structural transitions. The properties of designed structures can be of interest of catalysts and biosensors for biomedical applications.

https://doi.org/10.1016/j.apsusc.2020.148223

Synthesis, Crystal Structure and Thermodynamic Properties of LuGaTi2O7

L. T. Denisova, M. S. Molokeev, L. G. Chumilina, Yu. F. Kargin, V. M. Denisov & V. V. Ryabov . Inorganic Materials . DOI https://doi.org/10.1134/S0020168520120055

Single-phase LuGaTi2O7 samples have been prepared by solid-state reaction in a starting mixture of Lu2O3, Ga2O3, and TiO2 via sequential firing in air at temperatures of 1273 and 1573 K. The crystal structure of the lutetium gallium dititanate has been determined by the Rietveld method (profile analysis of X-ray diffraction patterns of polycrystalline powders): sp. gr. Pcnb; a = 9.75033(13) Å, b = 13.41425(17) Å, c = 7.29215(9) Å, V = 957.32(2) Å3, d = 6.28 g/cm3. The heat capacity of LuGaTi2O7 has been determined as a function of temperature by differential scanning calorimetry in the range 320–1000 K. The Cp(T) data thus obtained have been used to calculate the principal thermodynamic functions of the oxide compound.

DOIhttps://doi.org/10.1134/S0020168520120055

Chaotic and Regular Dynamics In the Three-site Bose-Hubbard Model

Bychek, Anna A.; Muraev, Pavel S.; Maksimov, Dmitrii N. et all AIP Conference Proceedings https://doi.org/10.1063/5.0011540

We analyze the energy spectrum of the three-site Bose-Hubbard model. It is shown that this spectrum is a mixture of the regular and irregular spectra associated with the regular and chaotic components of the classical Bose-Hubbard model. We find relative volumes of these components by using the pseudoclassical approach. Substituting these values in the Berry-Robnik distribution for the level spacing statistics we obtain good agreement with the numerical data.

https://doi.org/10.1063/5.0011540

Dielectric database of organic Arctic soils (DDOAS)

Savin, Igor; Mironov, Valery; Muzalevskiy, Konstantin; Fomin, Sergey; Karavayskiy, Andrey; et al. Earth System Science Data. https://doi.org/10.5194/essd-12-3481-2020

This article presents a dielectric database of organic Arctic soils (DDOAS). The DDOAS was created based on the dielectric measurements of seven samples of organic-rich soils collected in various parts of the Arctic tundra: Yamal Peninsula, Taimyr Peninsula, Samoylov Island (all in the Russian Federation) and the northern slope of Alaska (US). The organic matter content (by weight) of the presented soil samples varied from 35 % to 90 %. The refractive index (RI) and normalised attenuation coefficient (NAC) were measured under laboratory conditions by the coaxial-waveguide method in the frequency range from ∼ 10 MHz to ∼ 16 GHz, while the moisture content changed from air-dry to field capacity, and the temperature changed from −40 to +25 ∘C. The total number of measured values of the RI and NAC contained in the database is more than 1.5 million. The created database can serve not only as a source of experimental data for the development of new soil dielectric models for the Arctic tundra but also as a source of training data for artificial intelligence satellite algorithms of soil moisture retrievals based on neural networks. The DDOAS is presented as Excel files. The files of the DDOAS are available on https://doi.org/10.5281/zenodo.3819912 (Savin and Mironov, 2020).

The effect of the impurities on the magnetic, electronic and optical properties of Mn5Ge3

Zhandun, Vyacheslav; Matsynin, Aleksey Chinese Journal Of Physics. https://doi.org/10.1016/j.cjph.2020.06.027

Earlier, we experimentally showed a significant effect of oxygen on the magnetic and structural properties of Mn5Ge3 due to the formation of a Nowotny phase of Mn5Ge3Ox. Here, in continuation of this study, we present a theoretical study of the magnetic and electronic properties of Mn5Ge3 and Mn5Ge3Dx (D = B, C, O). It was found that hexagonal Mn5Ge3 is a ferromagnetic metal with two nonequivalent manganese atoms in the structure. Our ab initio calculations also predict the existence of a spin-crossover in Mn5Ge3 under pressure. Impurities reduce saturation magnetization and electrical and thermal conductivity; however, the magnetic susceptibility and Curie temperature increase. Microscopic mechanisms of the effect of the impurities on the magnetic and electronic properties Mn5Ge3 are discussed.

Highly Porous Superconductors: Synthesis, Research, and Prospects

Gokhfeld, D. M.; Koblischka, M. R.; Koblischka-Veneva, A. Physics Of Metals And Metallography. DOI https://doi.org/10.1134/S0031918X20100051

This paper presents a review of studies of superconductors with a porosity above 50%. The pores in such superconducting materials allow refrigerant penetration and provide efficient heat dissipation and stable operation. Methods for the synthesis of the main groups of porous superconductors are described. The results of studies of the structural, magnetic, and electrical transport properties are presented, and the features of the current flow through porous superconductors of various types are considered. The directions of further development and application of porous superconductors are presented.

DOIhttps://doi.org/10.1134/S0031918X20100051

Single-layer polymeric tetraoxa[8]circulene modified by s-block metals: toward stable spin qubits and novel superconductors

Begunovich, Lyudmila V.; Kuklin, Artem V.; Baryshnikov, Gleb V.; Valiev, Rashid R.; Agren, Hans. Nanoscale. DOI: 10.1039/D0NR08554E

Tunable electronic properties of low-dimensional materials have been the object of extensive research, as such properties are highly desirable in order to provide flexibility in the design and optimization of functional devices. In this study, we account for the fact that such properties can be tuned by embedding diverse metal atoms and theoretically study a series of new organometallic porous sheets based on two-dimensional tetraoxa[8]circulene (TOC) polymers doped with alkali or alkaline-earth metals. The results reveal that the metal-decorated sheets change their electronic structure from semiconducting to metallic behaviour due to n-doping. Complete active space self-consistent field (CASSCF) calculations reveal a unique open-shell singlet ground state in the TOC–Ca complex, which is formed by two closed-shell species. Moreover, Ca becomes a doublet state, which is promising for magnetic quantum bit applications due to the long spin coherence time. Ca-doped TOC also demonstrates a high density of states in the vicinity of the Fermi level and induced superconductivity. Using the ab initio Eliashberg formalism, we find that the TOC–Ca polymers are phonon-mediated superconductors with a critical temperature TC = 14.5 K, which is within the range of typical carbon based superconducting materials. Therefore, combining the proved superconductivity and the long spin lifetime in doublet Ca, such materials could be an ideal platform for the realization of quantum bits.

Mie Resonance Engineering in Two Disks

Bulgakov, Evgeny; Pichugin, Konstantin; Sadreev, Almas Photonics. https://doi.org/10.3390/photonics8020049

Recently the recipes to achieve the high-Q subwavelength resonances in an isolated dielectric disk have been reported based on avoided crossing (anticrossing) of the TE resonances under variation of the aspect ratio of the disk. In a silicon disk that recipe gives an enhancement of the Q factor by one order of magnitude. In the present paper we present the approach based on engineering of the spherical Mie resonances with high orbital index in two coaxial disks by two-fold avoided crossing of the resonant modes of the disks. At the first step we select the resonant modes of single disk which are degenerate because of the opposite symmetry. Approaching of the second disk removes this degeneracy because of interaction between the disks. As a result at certain distances we realize the hybridized anti-bonding resonant modes whose morphology becomes close to the spherical Mie resonant mode with high orbital index. Respectively the Q factor of the anti-bonding resonant mode can be enhanced by three orders of magnitude compared to the case of single disk. 

The Sr2.4Dy0.6Co2O7-delta Ruddlesden-Popper Phase: Structural, thermoelectric, and magnetic properties

Dudnikov, V. A.; Orlov, Yu S.; Solovyov, L. A.; Vereshchagin, S. N.; Gavrilkin, S. Yu Ceramics International. https://doi.org/10.1016/j.ceramint.2020.12.030

A new anion-deficient Sr2.4Dy0.6Co2O7‒δ (δ = 0.33–1.1) perovskite phase with a structure of the A3B2O7 Raddlesden‒Popper homologous series has been obtained by the solid-state synthesis in the reducing/oxidizing atmosphere and its structural characterization has been performed by the Rietveld refinement of the X-ray powder diffraction data. It has been stablished that the Sr2.4Dy0.6Co2O7‒δ compound (sp. gr. I4/mmm) has parameters of a = b = 3.8526(1) and c = 19.9431(7) Å in the reduced form (δ = 1.1) and a = b = 3.8086(1) and c = 19.9190(6) Å in the oxidized form (δ ≈ 0.33) and oxygen vacancies occupy mainly the sites linking CoO5 polyhedra inside two perovskite layers. It has been established using differential scanning calorimetry and thermogravimetry that, at T < 530 K, the synthesized phase is stable against the inert and oxidizing atmosphere; at higher temperatures, the Sr2.4Dy0.6Co2O7-δ compound can reversibly absorb/release oxygen. The magnetic properties of the Sr2.4Dy0.6Co2O6.09 compound have been investigated in the temperature range of 10–400 K and described in terms of the formation of dimers, in which the Co3+‒Co3+ and Co2+‒Co2+ ion pairs antiferromagnetically interact and are in the nonmagnetic ground state. The electrical conductivity and the Seebeck coefficient have been measured in air in the temperature range from 300 to 800 K. An observed sharp decrease in the Seebeck coefficient of the Sr2.4Dy0.6Co2O7-δ compound and the change in its sign near 700 K have been attributed to the transition of cobalt ions to the Co3+ state and the charge disproportionation of Co3+ ions to Co2+ and Co4+ ones.

Manipulation of Cl/Br transmutation in zero-dimensional Mn2+-based metal halides toward tunable photoluminescence and thermal quenching behaviors

Guojun Zhou ORCID logoa, Zhiyang Liu ORCID logob, Maxim S. Molokeev ORCID logocde, Zewen Xiao ORCID logob, Zhiguo Xia ORCID logof and Xian-Ming Zhang ORCID logo*a. JOURNAL OF MATERIALS CHEMISTRY C. DOI: 10.1039/D0TC05137C

Low-dimensional-networked metal halides are attractive for the screening of emitters applied in solid-state lighting and displays, but the lead toxicity and poor stability are obstacles that must be overcome in industrial applications. Herein, we aim at the discovery of bright and stable photoluminescence in zero-dimensional (0D) Mn2+-based metal halides. By manipulation of Cl/Br transmutation, the nature of the halogen can be confirmed as a pivotal factor to tune the PL behaviors, and the optimum Mn2+ emission with a high PLQY of 99.8% and a short lifetime of 0.372 ms can be achieved in (C24H20P)2MnBr4. The thermal quenching behaviors have been discussed in depth, indicating that the synergistic effect of good chemical stability of organic groups, a long Mn⋯Mn distance of 10.447 Å and a relatively large activation energy (ΔE = 0.277 eV) provides a platform for achieving excellent thermal stability in (C24H20P)2MnBr4. Moreover, the as-fabricated white LED device with a high luminous efficacy of 118.9 lm W−1 and a wide color gamut of 105.3% National Television System Committee (NTSC) shows that (C24H20P)2MnBr4 can be employed as a desirable narrow-band green emitter for LED displays. This work provides a new understanding of fine tailoring halogens, and proposes a feasible approach to achieving high thermal stability emitters toward the targeted practical applications.

DOI: 10.1039/D0TC05137C

Vibrational resonant inelastic X-ray scattering in liquid acetic acid: a ruler for molecular chain lengths

Savchenko, Viktoriia; Brumboiu, Iulia Emilia; Kimberg, Victor; et all. SCIENTIFIC REPORTS DOI: 10.1038/s41598-021-83248-3

Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.

DOI: https://doi.org/10.1038/s41598-021-83248-3

Polarization-sensitive IR-pump-x-ray-probe spectroscopy

Ji-Cai Liu, Viktoriia Savchenko, Victor Kimberg, Michael Odelius, and Faris Gel'mukhanov. Phys. Rev. A. DOI: 10.1103/PhysRevA.103.022829

X-ray absorption and core-ionization spectra of molecules pumped by two coherent infrared pulses with different polarizations are studied theoretically. We have found a sensitivity of the vibrational profile of x-ray probe spectra to polarizations of the IR and x-ray pulses. This polarization dependence is qualitatively different for x-ray absorption and x-ray photoelectron spectra. Measurements of this polarization dependence allow to select the difference in Franck-Condon distributions from the lowest and pumped vibrational levels of the electronic ground state. The proposed technique is exemplified numerically using x-ray absorption spectra of the pumped CO molecule. We also show that this kind of pump-probe spectroscopy can enable studies of the dynamics of molecular rotation.

DOI: 10.1103/PhysRevA.103.022829

Solid-state synthesis, rotatable magnetic anisotropy and characterization of Co1-xPtx phases in 50Pt/50fccCo(001) and 32Pt/68fccCo(001) thin films

Myagkov, V. G.; Bykova, L. E.; Zhigalov, V. S.; с соавторами. JOURNAL OF ALLOYS AND COMPOUNDS. https://doi.org/10.1016/j.jallcom.2020.157938

We reported the phase formation sequences in 50Pt/50fcc-Co(001) and 32Pt/68fcc-Co(001) thin films after annealing up to 850 °C. In both cases, the ordered L10 phase formed first on the Pt/Co interface at ∼400 °C and as the annealing temperature increased the L10 phase transformed into the chemically disordered fcc A1 phase in 50Pt/50fcc-Co(001) at 750 °C and in 32Pt/68fcc-Co(001) films at 550 °C. Based on the analysis of solid-state reactions in thin films, a phase transition at ∼ 400 °C is predicted in Co-Pt systems with a 32–72% Pt composition. Torque measurements of the 50Pt/50fcc-Co(001) samples showed that the rotatable magnetic anisotropy coexisted with the three variants of L10 in a temperature range of 400–750 °C. An analysis of the torque curves revealed that the L10 films consist of a soft magnetic layer epitaxially intergrown to the substrate MgO(001) and a top layer having rotatable magnetic anisotropy. It showed that the magnetically hard properties of L10 films are associated with a rotatable magnetic anisotropy layer. A model of rotatable magnetic anisotropy is reasoned, which is founded on some identical mechanisms of rotatable magnetic anisotropy and magnetic-field-induced strains, explaining the ferromagnetic shape-memory effect in Heusler alloys. Our results suggested that the rotatable magnetic anisotropy phenomena may have an important role in the origin of perpendicular anisotropy in hard magnetic L10

https://doi.org/10.1016/j.jallcom.2020.157938

Critical coupling vortex with grating-induced high Q-factor optical Tamm states

Bikbaev, Rashid G.; Maksimov, Dmitrii N.; Pankin, Pavel S.; Chen, Kuo-Ping; Timofeev, Ivan, V. Optics Express. https://doi.org/10.1364/OE.416132

We investigate optical Tamm states supported by a dielectric grating placed on top of a distributed Bragg reflector. It is found that under certain conditions the Tamm state may become a bound state in the continuum. The bound state, in its turn, induces the effect of critical coupling with the reflectance amplitude reaching an exact zero. We demonstrate that the critical coupling point is located in the core of a vortex of the reflection amplitude gradient in the space of the wavelength and angle of incidence. The emergence of the vortex is explained by the coupled mode theory.

High-Temperature Evolution of the Magnetization of Aluminum Reduction Cell Steel

Balaev, Dmitry A.; Semenov, Sergei, V; Varnakov, Sergei N.; Radionov, Evgeniy Yu; Al Tretyakov, Yaroslav. Journal Of Siberian Federal University-mathematics & Physics DOI: https://doi.org/10.17516/1997-1397-2021-14-1-5-11

The magnetic properties of steel of a structural element of an aluminum reduction cell have been investigated in the temperature range of 300–900 K. The analysis of the temperature dependence of the saturation magnetization MS(T) showed (i) the applicability of the Bloch’s 3/2 law and a reasonable value of the Bloch’s constant for steel and (ii) the quadratic dependence MS(T)∼(1 − T 2 ) in the temperature range of 380–700 K.

DOI: https://doi.org/10.17516/1997-1397-2021-14-1-5-11

Admittance spectroscopy of dopants implanted in silicon and impurity state-induced AC magnetoresistance effect

Smolyakov, D. A.; Tarasov, A. S.; Bondarev, M. A.; Nikolskaya, A. A.; Vasiliev, V. K.; et al. Materials Science In Semiconductor Processing. https://doi.org/10.1016/j.mssp.2021.105663

A silicon structure doped with Ga using ion implantation has been investigated by admittance spectroscopy. It has been established that the presence of the Ga impurity, along with the B one, in the silicon structure leads to the appearance of the second peak in the temperature dependence of the real part of the impedance (admittance). Moreover, switching-on a magnetic field parallel to the sample plane shifts the singularities in the temperature curve to the high-temperature region. This results in the manifestation of both the positive and negative magnetoresistance effect upon temperature and magnetic field variation. It has been found by the standard admittance spectroscopy analysis of the impedance data that the energy structure of the investigated sample includes two interfacial energy levels ES1(0) = 42 meV and ES2(0) = 69.4 meV. As expected, these energies are consistent with the energies of B and Ga dopants. In a magnetic field, these levels increase by 3 meV for B and 2 meV for Ga, which induces the magnetoresistance effect. It has been demonstrated that the interfacial state-induced magnetoresistance effect can be tuned by ion implantation and dopant selection.

 

https://doi.org/10.1016/j.mssp.2021.105663

Square plate shaped magnetite nanocrystals

Komogortsev, S., V; Stolyar, S., V; Chekanova, L. A.; Yaroslavtsev, R. N.; Bayukov, O. A.; et al. Journal Of Magnetism And Magnetic Materials. https://doi.org/10.1016/j.jmmm.2021.167730

Square plate shaped magnetite nanocrystals have been synthesized by chemical precipitation from solution using arabinogalactan. A high crystal quality was observed in the plate plane while, across the plate, there is some stratification. The magnetic hysteresis in such particles is determined by the bulk magnetocrystalline anisotropy, plate shape anisotropy, and surface magnetic anisotropy. It is shown using the micromagnetic simulation that the ferromagnetic square nanoplates exhibit the extraordinary magnetization switching anisotropy, which should be taken into account for understanding the hysteretic properties of the particles.

Temperature-dependent Raman spectroscopy, domain morphology and photoluminescence studies in lead-free BCZT ceramic

Coondoo, Indrani; Panwar, Neeraj; Krylova, Svetlana; с соавторами. CERAMICS INTERNATIONAL. DOI: 10.1016/j.ceramint.2020.09.137

Present work focuses on detailed temperature-dependent X-ray diffraction, Raman scattering, domain configuration, and photoluminescence (PL) studies in the (Ba0.85Ca0.15) (Zr0.10Ti0.90)O-3 (BCZT) ceramics. The comprehensive Raman spectroscopy analysis in the present work not only validates the presence of the intermediate orthorhombic phase in BCZT, but also provides evidence of another transition: rhombohedral R3c phase to R3m at low temperature. Temperature behaviour of the lowest frequency transverse optical mode (soft E (TO) phonon) and hard modes was studied. Temperature dependence of peak positions, intensities, and linewidths of Raman phonon modes signalled the presence of phase transitions near-50 +/- 5 degrees C, 0 +/- 5 degrees C, 35 +/- 5 degrees C and 110 +/- 10 degrees C. Evolution of domain morphology occurring at phase transitions above room temperature was studied by piezoresponse force microscopy technique. Analysis of PL spectra revealed disorder/heterogeneity in the sample and indicated the existence of self-trapped excitons. PL spectra are composed of four distinct colour components (-2.55eV:blue, -2.32eV:green, -2.08eV:orange and -1.78eV:red).

DOI: 10.1016/j.ceramint.2020.09.137

Kramers Degeneracy and Spin Inversion in a Lateral Quantum Dot

Pichugin, Konstantin; Puente, Antonio; Nazmitdinov, Rashid SYMMETRY-BASEL. DOI: 10.3390/sym12122043

We show that the axial symmetry of the Bychkov-Rashba interaction can be exploited to produce electron spin-flip in a circular quantum dot, without lifting the time reversal symmetry. In order to elucidate this effect, we consider ballistic electron transmission through a two-dimensional circular billiard coupled to two one-dimensional electrodes. Using the tight-binding approximation, we derive the scattering matrix and the effective Hamiltonian for the considered system. Within this approach, we found the conditions for the optimal realization of this effect in the transport properties of the quantum dot. Numerical analysis of the system, extended to the case of two-dimensional electrodes, confirms our findings. The relatively strong quantization of the quantum dot can make this effect robust against the temperature effects.

DOI:  https://doi.org/10.3390/sym12122043

Synthesis and luminescent properties of (RE(0.)(95)Ln(0.)(05))(2)O2S (RE = La, Y; Ln = Ho, Tm)

Sal'nikova, E., I; Denisenko, Yu G.; Kolesnikov, I. E.; с соавторами. JOURNAL OF SOLID STATE CHEMISTRY. https://doi.org/10.1016/j.jssc.2020.121753

Solid solutions of oxysulfides (RE0.95Ln0.05)2O2S (RE = La, Y; Ln = Ho, Tm) were obtained by hydrogen reduction of the co-precipitated sulfates followed by sulfidation of the reaction products. The crystal chemical characteristics of the obtained compounds were refined by the Rietveld method. Morphological certification of particles in the dynamics of synthesis was performed. Most of the particles produced by chemical reactions have a cut that indicates the formation of a compound with a hexagonal syngony with angles of 60 and 120°. This indicates that the thermal effect of gaseous reagents H2, H2S on sulfates leads to heterogeneous reactions of thermal dissociation and the formation of new phases. Steady state luminescence properties displayed characteristic sharp bands corresponding to 4f-4f transitions. Luminescence decay curves of all studied samples showed monoexponential decay with microsecond and hundreds microsecond lifetimes depending on doping ions. Calculated color coordinates of Ho3+ and Tm3+-doped powders make them promising candidates to be used as phosphors.

https://doi.org/10.1016/j.jssc.2020.121753

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