New Publications

Coordination units of Mn2+ modulation toward tunable emission in zero-dimensional bromides for white light-emitting diodes

Zhou, Guojun; Ding, Jialiang; Jiang, Xingxing; Zhang, Jian; Molokeev, Maxim S.; et al.// Journal Of Materials Chemistry C//

DOI: https://doi.org/10.1039/D1TC05680H

Organic–inorganic metal halides have become a multifunctional platform for manipulating photoluminescence due to highly efficient and tunable emissions, especially for lead-free Mn2+-based halides. Herein, the zero-dimensional (0D) bromides of (C5H14N3)2MnBr4 and (CH6N3)2MnBr4 with different coordination environments were designed and synthesized by a solvent evaporation method. They exhibit green and red broadband emission peaks at 528 nm and 627 nm with high photoluminescence quantum yields of 86.83% and 61.91%, respectively, which are attributed to the d–d transition (4T1(G) → 6A1(S)) of [MnBr4]2− tetrahedral and [Mn3Br12]6− octahedral units. The cases emphasize the effect of organic ligands on the intrinsic emissions of Mn2+ ions, thereby revealing the luminescence mechanism of Mn2+ ions in 0D isolated structures through the Tanabe–Sugano (TS) energy diagram. Thanks to their bright and stable emissions, the fabricated white light-emitting diode (LED) based on (C5H14N3)2MnBr4 and (CH6N3)2MnBr4 provides an outstanding color rendering index (Ra) of 90.8 at a correlated color temperature (CCT) of 3709 K, along with the CIE chromaticity coordinates of (0.3985, 0.3979) and a luminous efficacy of 51.2 lm W−1. This work aims at clarifying the relationship between the coordination units of Mn2+ and tunable emissions, and in particular, proposes a new strategy to explore phosphors excited by blue light for white LEDs.

Tailoring the microwave properties of thin Permalloy films using a periodically grooved substrate

Izotov, A., V; Belyaev, B. A.; Boev, N. M.; Burmitskikh, A., V; Leksikov, A. A.; et al.// Physica B-condensed Matter//

https://doi.org/10.1016/j.physb.2021.413654

Thin magnetic films with periodic surface topography are of special interest for microwave applications as their static and dynamic magnetic characteristics can be readily adjusted. In this paper, we explore the capabilities of a simple method for producing large-area periodically patterned films by creating regularly spaced grooves on a substrate using a diamond cutter. For 110-nm-thick films, it was found that the substrate-topography-induced magnetic anisotropy was inversely proportional to the pattern period, which in experimental samples varied from 5 to 20 μm. Based on the Netzelmann theory, analytical expressions for demagnetization tensor components were obtained, which accord well with the experimental data. The measurements of the natural ferromagnetic resonance spectra demonstrated that the increase of the topography-induced magnetic anisotropy with the decrease of the pattern period led to the increase of the resonance frequency from 0.65 to 1.86 GHz, and to a decrease of the linewidth and effective damping parameter.

Bacterial Cellulose (BC) and BC Composites: Production and Properties

Volova, Tatiana G. G.; Prudnikova, Svetlana V. V.; Kiselev, Evgeniy G. G.; Nemtsev, Ivan V. V.; Vasiliev, Alexander D. D.; et al. Nanomaterials

https://doi.org/10.3390/nano12020192

The synthesis of bacterial cellulose (BC) by Komagataeibacter xylinus strain B-12068 was investigated on various C-substrates, under submerged conditions with stirring and in static surface cultures. We implemented the synthesis of BC on glycerol, glucose, beet molasses, sprat oil, and a mixture of glucose with sunflower oil. The most productive process was obtained during the production of inoculum in submerged culture and subsequent growth of large BC films (up to 0.2 m2 and more) in a static surface culture. The highest productivity of the BC synthesis process was obtained with the growth of bacteria on molasses and glycerol, 1.20 and 1.45 g/L per day, respectively. We obtained BC composites with silver nanoparticles (BC/AgNPs) and antibacterial drugs (chlorhexidine, baneocin, cefotaxime, and doripenem), and investigated the structure, physicochemical, and mechanical properties of composites. The disc-diffusion method showed pronounced antibacterial activity of BC composites against E. coli ATCC 25922 and S. aureus ATCC 25923. 

Machine Learning Analysis and Discovery of Zero-Dimensional ns(2) Metal Halides toward Enhanced Photoluminescence Quantum Yield

Molokeev, Maxim S.; Su, Binbin; Aleksandrovsky, Aleksandr S.; Golovnev, Nicolay N.; Plyaskin, Mikhail E.; et al.// Chemistry Of Materials//

https://doi.org/10.1021/acs.chemmater.1c02725

The dependence of photoluminescence quantum yield (PLQY) on the crystal structure of existing zero-dimensional ns2 metal halides is analyzed with the help of principal component analysis and random forest methods. The primary role of the distance between metal ions in different compounds is revealed, and the influence of other structural features such as metal-halogen distance and the distortion of metal-halogen polyhedrons are quantified. Accordingly, the two previously unknown Sb3+-based zero-dimensional metal halides were synthesized to verify the obtained model. Experimental studies of the two compounds demonstrated good agreement with the predictions, and the PLQY of (C10H16N)2SbCl5 is found to be 96.5%. Via machine learning analysis, we demonstrate that concentration quenching is the main factor that determines PLQY for all s2 ion metal halides, which will accelerate the discovery of new luminescence metal halides.

Magnetoresistance and magnetoimpedance in holmium manganese sulfides

Romanova, O. B.; Aplesnin, S. S.; Sitnikov, M. N.; Udod, L., V; Kharkov, A. M.// Applied Physics A-materials Science & Processing//

https://doi.org/10.1007/s00339-021-05198-x

The structure, transport characteristics, real and imaginary parts of the impedance components and electric polarization of the HoXMn1−XS (X = 0.1 and 0.2) system have been investigated in the temperature range of 80‒500 K in magnetic fields of up to 12 kOe. The morphology of synthesized samples has been studied. The influence of the magnetic field on the transport characteristics, on both direct and alternating currents of holmium manganese sulfides, have been established. The negative effects of DC magnetoresistance in the region of the magnetic phase transition and positive AC magnetoimpedance up to 4% in the paramagnetic region have been established. The critical temperatures of the existence of the electric polarization have been determined. At a substitution concentration of X = 0.1, the activation character of the relaxation time versus temperature has been found. The diffusion contribution for the composition with X = 0.2 has been established by the impedance hodograph.

Asymmetric Interfaces in Epitaxial Off-Stoichiometric Fe3+xSi1-x/Ge/Fe3+xSi1-x Hybrid Structures: Effect on Magnetic and Electric Transport Properties

Tarasov, Anton S.; Tarasov, Ivan A.; Yakovlev, Ivan A.; Rautskii, Mikhail V.; Bondarev, Ilya A.; et al.// Nanomaterials//

 https://doi.org/10.3390/nano12010131

Three-layer iron-rich Fe3+xSi1−x/Ge/Fe3+xSi1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe3+xSi1−x heterosystem due to the incorporation of Ge atoms into the Fe3+xSi1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe3+xSi1−x. The average lattice distortion and residual stress of the upper Fe3+xSi1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe3+xSi1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe3+xSi1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe3+xSi1−x, which implies the epitaxial orientation relationship of Fe3+xSi1−x (111)[0−11] || Ge(111)[1−10] || Fe3+xSi1−x (111)[0−11] || Si(111)[1−10]. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms. 

Subterahertz and terahertz spin and lattice dynamics of the insulating ferromagnet PbMnBO4

Prosnikov, M. A.; Bal, M. E.; Kolkov, M., I; Pankrats, A., I; Pisarev, R., V; et al.// Physical Review Research//

 

DOI:https://doi.org/10.1103/PhysRevResearch.4.013004

Orthorhombic PbMnBO4 is a rare example of an insulating ferromagnet in which the magnetic properties, in particular the strong magnetic anisotropy, are determined by the Mn3+ Jahn-Teller ion. Here, we report on the detailed investigation of magnetic excitations in the subterahertz and terahertz frequency ranges, as well as lattice excitations in the terahertz range. Using polarized azimuthally resolved Raman spectroscopy, four branches of magnetic excitations were observed and assigned to one acoustic and three optical one-magnon modes. The coupling between ferromagnetic ordering at TC=31K and the Jahn-Teller distortions of [MnO6] octahedra due to the spin-phonon interaction was directly observed for some specific phonon modes involved in these distortions. A spin-wave Hamiltonian was developed that allowed us to determine a unique set of exchange and effective anisotropy parameters. The intensity ratio of the anti-Stokes to Stokes acoustic magnon peaks is found to be anomalous and directly indicates the involvement of the magneto-optical parameters in the magnetic Raman scattering process.

LIQUID CRYSTAL MATERIALS UNDER CONICAL BOUNDARY CONDITIONS

Krakhalev, M. N.; Rudyak, V. Yu; Sutormin, V. S.; Prishchepa, O. O.; Bikbaev, R. G.; et al.// Liquid Crystals And Their Application//

 https://doi.org/10.3390/cryst9050249

Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch.

Synthesizing Zinc Sulfide Films on the Gold Surface as the Sensor for Electrochemical Quartz Crystal Microbalance

Krinitsyn, D. O.; Romanchenko, A. S.; Vorob'ev, S. A.; Likhatskii, M. N.; Karacharov, A. A.; et al.// Russian Journal Of Electrochemistry//

https://doi.org/10.1134/S1023193521120041

A zinc sulfate film is deposited from aqueous solutions of zinc sulfate onto the gold surface with the aim of preparation of a sensor for electrochemical quartz crystal microbalance (EQCM). The kinetics of this process, the particles formed in solution, and the film itself are studied by the methods of electrochemical quartz crystal microbalance, X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy, optical and Raman spectroscopies, and dynamic light scattering. The effect of the procedure of gold surface preparation, the reagent concentration, and the temperature on the film adhesion, the length of induction period, the kinetics of film growth, and its structure and thickness are studied. It is shown that the film formation proceeds as a result of deposition of sufficiently coarse 200–700 nm colloid particles of sphalerite. It is demonstrated that this sensor can be used in studying the electrochemical reactions of ZnS and the interface phenomena by the methods of EQCM and cyclic voltammetry.

Structural, thermal and electrical studies of thallium-scandium-hafnium(zirconium) molybdates

Victoria G.Grossman, Maxim S.Molokeev, Jibzema G.Bazarov, Bair G.Bazarova, Nikolay I.Sorokin// Journal of Solid State Chemistry//

https://doi.org/10.1016/j.jssc.2021.122832

Thallium scandium hafnium molybdate Tl5ScHf(MoO4)6 and thallium scandium zirconium molybdate Tl5ScZr(MoO4)6 crystallize in trigonal symmetry with the space group R3¯c. The compounds are synthesized by sintering the finely powdered simple molybdates mixture in a muffle furnace at 723–823 K for 100 h. The crystal structures of Tl5ScHf(MoO4)6 and Tl5ScZr(MoO4)6 are obtained by Rietveld method. The following unit cell parameters are calculated for Tl5ScHf(MoO4)6: a = 10.62338 (5), c = 38.0579 (2) Å, V = 3719.64 (4) Å3, Z = 6 and for Tl5ScZr(MoO4)6: a = 10.63216 (7), c = 38.0716 (3) Å, V = 3727.14 (5) Å3, Z = 6. The conductivity of the Tl5ScHf(MoO4)6 and Tl5ScZr(MoO4)6 are measured between 293 and 860 K. The ionic conductivity of Tl5ScHf(MoO4)6 and Tl5ScZr(MoO4)6 molybdates are 8 × 10−4 S/cm and 8 × 10−3 S/cm (at 773 K); the activation energy of ionic transfer are 0.8 eV and 0.3 eV respectively.

Raman scattering study of the rare-earth binary ferroborate Nd0.75Dy0.25Fe3(BO3)(4) single crystal

Glamazda, AY, Gnezdilov, VP, Lemmens, P, Zvyagina, GA , Gudim, IA // LOW TEMPERATURE PHYSICS//

Doi:10.1063/10.0007074

We report comprehensive Raman scattering measurements on a single crystal of binary ferroborate Nd0.75Dy0.25Fe3(BO3)(4) in the temperature range of 7-295 K with 532 nm (18797 cm(-1)) laser excitation. The performed analysis of the polarized Raman spectra revealed the bands assigned to phonon, magnetic, and electronic excitations. The temperature evolution of these quasiparticle excitations has allowed us to ascertain the intricate coupling and interplay between lattice, magnetic, and electronic degrees of freedom. Analysis of the measured Raman spectra made it possible to identify all A(1) and E phonon modes predicted by the group-theoretical analysis. The splitting energies between the LO and TO components of the polar E phonons were determined. Below the magnetic ordering temperature of the Fe sublattice, T-N, we have revealed a multiple peaked two-magnon excitation. Analyzing the temperature evolution of low-frequency modes in the spectra, we also identified modes that are associated with electronic transitions between the crystal field levels of the Nd3+ ions with ground-state I-4(9/2) and of the Dy3+ ions with ground-state H-6(15/2) multiplets. In addition to the already known temperatures of magnetic transitions, analysis of the temperature behavior of low-frequency phonon and electronic excitations made it possible to establish a temperature T* = 100 K, presumably associated with local distortions of the crystal lattice. The presence of this temperature is confirmed by our ultrasonic study. A group of intense bands observed in the frequency range 1700-2200 cm(-1) has been associated with the mixed low-lying electronic Raman transitions I-4(9/2)& RARR;I-4(11/2) and the high-energy luminescence ones (4)G(5/2)+(2)G(7/2)& RARR;I-4(9/2) for the Nd3+ ion.

Desulfovibrio desulfuricans AY5 Isolated from a Patient with Autism Spectrum Disorder Binds Iron in Low-Soluble Greigite and Pyrite

Olga V. Karnachuk, Olga P. Ikkert, Marat R. Avakyan, Yurii V. Knyazev, Mikhail N.Volochaev, Viacheslav S. Zyusman, Vasily L. Panov, Vitaly V. Kadnikov ,Andrey V. Mardanov and Nikolai V. Ravin// MICROORGANISMS//

 https://doi.org/10.3390/microorganisms9122558

The sulphate-reducing bacteria (SRB) of genus Desulfovibrio are a group of prokaryotes associated with autism spectrum disorders (ASD). The connection between the elevated numbers of Desulfovibrio in the gut of children with ASD compared with healthy children remains unresolved. A conceivable consequence of SRB overgrowth in the gut is the conversion of bioavailable iron into low-soluble crystalline iron sulphides, causing iron deficiency in the organism. In this study, we report the draft genome sequence and physiological features of the first cultivable isolate from a patient with ASD, Desulfovibrio desulfuricans strain AY5.The capability of the strain to produce crystalline iron sulphides was studied under different pH conditions. The most notable greigite(Fe3S4) and pyrite (FeS2) formation was revealed at pH 6.0, which suggests that the iron loss due to insoluble sulphide formation may occur in the proximal part of the gastrointestinal tract. Strain AY5 was adapted to grow under nitrogen-limiting conditions by N2 fixation. The urease found in the strain’s genome may play a role in resistance to acidic pH.

Unveiling White Light Emission of a One-Dimensional Cu(I)-Based Organometallic Halide toward Single-Phase Light-Emitting Diode Applications

Jinglong Huang, Yinhui Peng, Jiance Jin, Maxim S. Molokeev, Xiaobao Yang, and Zhiguo Xia// JOURNAL OF PHYSICAL CHEMISTRY LETTERS//

https://doi.org/10.1021/acs.jpclett.1c03767

Luminescent organometallic halide crystals, especially with single-component white emission, are urgently needed for light-emitting diode (LED) applications. Barriers for the applications, however, lie in their lead toxicity, poor stability, and low photoluminescence quantum yield (PLQY). Here, a one-dimensional Cu(I)-based hybrid metal halide (C12H24O6)CsCu2Br3 is designed and prepared via a simple solution method. Upon 365 nm excitation, a broad-band white light emission centered at 535 nm with a full width at half maximum of 186 nm and a PLQY of 78.3% is monitored. The experimental results together with calculation data indicate that the existence of the split peaks at 486 and 570 nm at a low temperature is attributed to the decrease of energy level degeneracy by virtue of the lattice distortion. Moreover, the stability along with the good device performance of the as-fabricated white LED was also discussed. The results demonstrate that (C12H24O6)CsCu2Br3 is highly competitive in lighting application, and it can further enable breakthrough material design for new luminescent organometallic halides.

Antimicrobial properties of nanofiltration membranes modified with silver nanoparticles

Renat Khaydarov, Olga Gapurova, Murodjon Abdukhakimov, Ilkham Sadikov, Ilnur Garipov, Praveen Thaggikuppe Krishnamurthy, Sergey M. Zharkov, Galina M. Zeer, Polina A. Abolentseva, Svetlana V. Prudnikova & Svetlana Y. Evgrafova // JOURNAL OF PHYSICAL CHEMISTRY LETTERS//

DOI: 10.1021/acs.jpclett.1c03767

Luminescent organometallic halide crystals, especially with single-component white emission, are urgently needed for light-emitting diode (LED) applications. Barriers for the applications, however, lie in their lead toxicity, poor stability, and low photoluminescence quantum yield (PLQY). Here, a one-dimensional Cu(I)-based hybrid metal halide (C12H24O6)CsCu2Br3 is designed and prepared via a simple solution method. Upon 365 nm excitation, a broad-band white light emission centered at 535 nm with a full width at half maximum of 186 nm and a PLQY of 78.3% is monitored. The experimental results together with calculation data indicate that the existence of the split peaks at 486 and 570 nm at a low temperature is attributed to the decrease of energy level degeneracy by virtue of the lattice distortion. Moreover, the stability along with the good device performance of the as-fabricated white LED was also discussed. The results demonstrate that (C12H24O6)CsCu2Br3 is highly competitive in lighting application, and it can further enable breakthrough material design for new luminescent organometallic halides

Field test of the surface soil moisture mapping using Sentinel-1 radar data

Zeyliger, A. M.; Muzalevskiy, K., V; Zinchenko, E., V; Ermolaeva, O. S. // Science Of The Total Environment//

https://doi.org/10.1016/j.scitotenv.2021.151121

Soil surface moisture is one of the key parameters for describing the hydrological state and assessing the potential availability of water for irrigated plants. Because the radar backscattering coefficient is sensitive to soil moisture, the application of Sentinel-1 data may support soil surface moisture mapping at high spatial resolution by detecting spatial and temporal changes at the field scale for precision irrigation management. This mapping is required to control soil water erosion and preferential water flow to improve irrigation water efficiency and minimise negative impacts on surface and ground water bodies.

EPR Study of the Single-Ion Magnetic Anisotropy of the Fe3+ Ion in a Diamagnetic PbGaBO4 Crystal

Vorotynov, A. M.; Pankrats, A., I; Kolkov, M., I // Journal Of Experimental And Theoretical Physics//

https://doi.org/10.1134/S1063776121110054

Crystals of a diamagnetic PbGaBO4 analog containing a small amount (about 0.5 at %) of Fe3+ ions are grown. The single-ion EPR spectra of Fe3+ in PbGa1 – xFexBO4 single crystals are analyzed with allowance for a crystal structure. The existence of four magnetically nonequivalent positions of Fe3+ ions with different local anisotropy axis directions has been confirmed. The parameters of the spin Hamiltonian written in the approximation of the local orthorhombic symmetry of a paramagnetic center are determined. The values of single-ion anisotropy constants, which are unusually high for S ions, is shown to be caused by a strong distortion of the ligand environment of Fe3+ ions. The single-ion contribution to the energy of the total magnetic anisotropy of a magnetically concentrated PbGaBO4 crystal is estimated. Two-ion mechanisms of the Fe–Fe interaction anisotropy are assumed to play a dominant role in the formation of magnetic anisotropy in a magnetically concentrated crystal.

Magneto-Optical Parameter Q for Structures with Uniaxial Optical Anisotropy

Maximova, O. A.; Lyaschenko, S. A.; Varnakov, S. N.; Ovchinnikov, S. G. // Journal Of Experimental And Theoretical Physics//

DOI: https://doi.org/10.1134/S1063776121110030

This paper is devoted to the development of reflection magneto-optical ellipsometry. We have solved the inverse problem for structures with uniaxial optical anisotropy: have determined the reflection coefficients for the ambient–sample interface, and have derived an analytic expression for magneto-optical parameter Q proportional to the magnetization. This expression makes it possible to determine parameter Q exclusively from experimental data obtained using magneto-optical ellipsometry. We present a detailed algorithm for performing experiment on determining the dielectric tensor in the transverse geometry.

Mechanisms of the Magnetoresistance Hysteresis in a Granular HTS with the Paramagnetic Contribution by the Example of HoBa2Cu3O7-delta

Semenov, S., V; Gokhfel'd, D. M.; Terent'ev, K. Yu; Balaev, D. A. // Physics Of The Solid State/

DOI: https://doi.org/10.1134/S1063783421100334

The hysteretic behavior of magnetoresistance R(H) of the granular high-temperature superconductor (HTS) HoBa2Cu3O7 – δ has been investigated. The YBCO superconductors with a rare-earth element (Nd, Ho, Er, Sm, Yb, or Dy) with the magnetic moment in the yttrium site are characterized by a significant paramagnetic contribution to the total magnetization. The main goal of this study has been to establish the possible effect of this paramagnetic contribution on the magnetotransport properties, which are determined by tunneling of superconducting current carriers through the grain boundaries. An analysis of the results obtained basing on the concept of an effective field in the intergrain medium showed that the distribution of the magnetic induction lines from the paramagnetic moments is fundamentally different from that of the Meissner currents and Abrikosov vortices. The magnetic induction lines from the paramagnetic moments are not concentrated in the region of grain boundaries and therefore insignificantly affect the magnetotransport properties of a granular HTS. At the same time, the magnetic induction lines are strongly concentrated in the grain boundaries, which is caused by the Meissner currents and Abrikosov vortices, due to the features of their properties. Specifically, the magnetic flux compression determines the magnetotransport (in particular, the R(H) hysteresis) properties of granular HTSs, including 1–2–3 ones, with a rare-earth ion with the magnetic moment.

Enhanced luminescence properties of Li2MgTiO4: Mn4+, Ge4+ phosphor via single cation substitution for indoor plant cultivation

Zhang, Sijin; Gai, Shujie; Zhang, Xiaojuan; Xia, Mao; Zhou, Zhi; et al. // Ceramics International/

https://doi.org/10.1016/j.ceramint.2021.10.082

Red and far-red emitting phosphors have been widely used in phosphor-converted light emitting diode (pc-LED) devices to provide lighting for indoor plant growth, thus achieving desired product qualities. Among the many ways to optimize phosphors’ optical performance, cationic substitution is one of the most effective methods. In this study, red phosphors (Li2MgTi1-x-yO4: xMn4+, yGe4+) were synthesized by high temperature solid state method and the optical performance of phosphors were improved with increasing Ge4+ constituents. In particular, luminescence intensity of Li2MgTiO4: 0.002Mn4+, 0.1Ge4+ increased by 152% under 468 nm excitation, and the thermostability of emission intensity increases from 22% (y = 0) to 43% (y = 0.1), which is about twice as much. Finally, pc-LED device was fabricated via the red phosphor Li2MgTiO4: 0.002Mn4+,0.1Ge4+ coated on a 470 nm ultraviolet chip. By changing the proportion of the phosphor, the electroluminescence spectra of pc-LED device could match well with the absorption regions of plant pigments. Therefore, Li2MgTiO4: 0.002Mn4+, 0.1Ge4+ phosphor has potential application in plant lighting. Furthermore, this work can offer some helpful references for improving luminescent efficiency by simply modulating the chemical composition.

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1-xCaGd0.5Ho0.05Yb0.45(MoO4)(3) Scheelite-Type Upconversion Phosphors

Lim, Chang-Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor // Molecules/

 https://doi.org/10.3390/molecules26237357

A set of new triple molybdates, LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45, was successfully manufactured by the microwave-accompanied sol–gel-based process (MAS). Yellow molybdate phosphors LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 with variation of the LixNa1-x (x = 0, 0.05, 0.1, 0.2, 0.3) ratio under constant doping amounts of Ho3+ = 0.05 and Yb3+ = 0.45 were obtained, and the effect of Li+ on their spectroscopic features was investigated. The crystal structures of LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) at room temperature were determined in space group I41/a by Rietveld analysis. Pure NaCaGd0.5Ho0.05Yb0.45(MoO4)3 has a scheelite-type structure with cell parameters a = 5.2077 (2) and c = 11.3657 (5) Å, V = 308.24 (3) Å3, Z = 4. In Li-doped samples, big cation sites are occupied by a mixture of (Li,Na,Gd,Ho,Yb) ions, and this provides a linear cell volume decrease with increasing Li doping level. The evaluated upconversion (UC) behavior and Raman spectroscopic results of the phosphors are discussed in detail. Under excitation at 980 nm, the phosphors provide yellow color emission based on the 5S2/5F4 → 5I8 green emission and the 5F5 → 5I8 red emission. The incorporated Li+ ions gave rise to local symmetry distortion (LSD) around the cations in the substituted crystalline structure by the Ho3+ and Yb3+ ions, and they further affected the UC transition probabilities in triple molybdates LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45. The complex UC intensity dependence on the Li content is explained by the specificity of unit cell distortion in a disordered large ion system within the scheelite crystal structure. The Raman spectra of LixNa1-xCaGd0.5(MoO4)3 doped with Ho3+ and Yb3+ ions were totally superimposed with the luminescence signal of Ho3+ ions in the range of Mo–O stretching vibrations, and increasing the Li+ content resulted in a change in the Ho3+ multiplet intensity. The individual chromaticity points (ICP) for the LiNaCaGd(MoO4)3:Ho3+,Yb3+ phosphors correspond to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates

Why the Magnetite-Gold Core-Shell Nanoparticles Are Not Quite Good and How to Improve Them

Sokolov, A. E.; Ivanova, O. S.; Fedorov, A. S.; Kovaleva, E. A.; Vysotin, M. A.; et al.// Physics Of The Solid State/

DOI: https://doi.org/10.1134/S1063783421090365

The nature of the formation of a chemical bond at the magnetite–gold interface has been studied. The geometric structure and the electronic and magnetic properties of plane layers consisting of magnetite Fe3O4 and gold have been investigated using the DFT-GGA calculation. It has been found that the specific energy and the wetting parameter of the magnetite–gold interface are negative, which leads to the island growth of small Au particles on the Fe3O4 surface. The role of an intermediate thin titanium layer between magnetite and gold has been discussed. The specific energy and wetting parameter of the magnetite–titanium (for thin Ti layers) and magnetite–titanium–gold interfaces are positive. It has been suggested that an intermediate thin titanium layer at the interface between the magnetite nanoparticle surface and the gold layer will make it possible to obtain magnetite nanoparticles with a continuous gold coating.

The Magneto-Optical Voigt Parameter from Magneto-Optical Ellipsometry Data for Multilayer Samples with Single Ferromagnetic Layer

Maximova, O.; Lyaschenko, S.; Tarasov, I; Yakovlev, I; Mikhlin, Y.; et al. // Physics Of The Solid State/

https://link.springer.com/article/10.1134%2FS1063783421090274

Calculations of the magneto-optical Voigt parameter Q were carried out using various models of reflecting media for thin films Fe|SiO2|Si(100) samples using the data of the in situ magneto-ellipsometry. The obtained spectral dependences of Q make it possible to choose the algorithm for the analysis of experimental magneto-ellipsometry data and demonstrate that magneto-optical parameter Q of iron is thickness-dependent.

The Magneto-Optical Voigt Parameter from Magneto-Optical Ellipsometry Data for Multilayer Samples with Single Ferromagnetic Layer

Maximova, O.; Lyaschenko, S.; Tarasov, I; Yakovlev, I; Mikhlin, Y.; et al. // Physics Of The Solid State/

Ground State of a Two-Sublattice Anisotropic Ferromagnet in a Magnetic Field

Martynov, S. N. // Physics Of The Solid State/

https://doi.org/10.1134/S1063783421080199

The ground state of a classical two-sublattice ferromagnet with the noncollinear single-ion anisotropy axes of the sublattices and the antisymmetric and anisotropic symmetric exchanges between them has been investigated in a magnetic field applied along the hard magnetization directions in the crystal. The threshold relations for the parameters of the anisotropic interactions have been obtained, which determine the choice of the ground state among the three possible magnetic phases. Depending on the ground state type and the field direction, the transition between the phases is a first- or second-order phase transition. The antisymmetric exchange value above which the reorientation between the noncollinear phases ends with a second-order transition depends on the angle between the local easy axes and the single-ion anisotropy value. Field dependences of the magnetization and susceptibility for different ground states have been calculated. A comparison with the results of the magnetic measurements in the highly anisotropic PbMnBO4 ferromagnet has been made.

Temperature dependent structural, dielectric, Raman, piezoresponse and photoluminescence investigations in sol-gel derived BCZT ceramics

Indrani Coondoo, Alexander Krylov, Dhananjay K.Sharma, Svetlana Krylova, Denis Alikin, J. Suresh Kumar, A.Mirzorakhimov, Nina Melnikova, Manuel J.Soares, Andrei L. Kholkin/ MATERIALS CHEMISTRY AND PHYSICS/

https://doi.org/10.1016/j.matchemphys.2021.125526

0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 [50BZT-50BCT or BCZT] based compounds have been the focus of a lot of research, particularly motivated by their high piezoelectric effect. However, the literature lacks an elaborate investigation of the phase transition behavior in BCZT ceramics obtained by wet chemistry processing. Here, we present an in-depth study on the temperature dependence of x-ray diffraction (XRD), Raman scatteringdielectric properties, local piezoresponse and photoluminescence (PL) to investigate the sequence of phase transitions in the BCZT ceramic synthesized via a chemical route. Phase formation was determined by Rietveld analysis of XRD data, while compositional homogeneity and elemental quantification of the compound was validated using energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS) studies. Detailed fitting of XPS data indicated the existence of Ti3+ species (∼6%) in the prepared BCZT. Phase transitions were examined by analyzing the modifications in the XRD profile of Bragg reflection {200} and anomalies observed in the temperature variation of dielectric and Raman spectra studied over a wide temperature range starting from 10K to beyond Curie temperature. Crystallographic transformation temperatures obtained from dielectric measurement agreed well with those assessed from the temperature evolution of Raman spectra. In addition to other transitions, Raman scattering results revealed the existence of a transition from R3c to R3m phase near −175 °C, a transition that has not been interpreted in BCZT (and generally not observed in parent BaTiO3 compound). The luminescence response was studied by photoluminescence (PL) spectroscopy in the temperature range 15–300 K. The position of the PL peak was observed to shift with temperature and discontinuities in the wavelength shift were noted near phase transitions. Evolution of domain morphology with temperature was examined by piezoresponse force microscopy technique.

Solid-State NMR Free Induction Decay, Simulated by the System of Classical Magnetic Moments and Quantum Correlations

Lundin, AA and Zobov, VE/ RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY/

DOI: https://doi.org/10.1134/S1990793121050079

In the past decade, nuclear magnetic resonance (NMR) has been actively used to study the basic principles of quantum computers. It is assumed that quantum correlations play a significant role in their performance. They exist at both low and high temperatures. At the same time, the time correlation functions of nuclear spin systems of solids determine the observed signals in traditional NMR implementations. The separation of such signals into quantum and classical components has not previously been carried out and will be performed in this study for the most important of the correlational functions observed in magnetic resonance: the free induction decay (FID).

Heat Capacity and Thermodynamic Functions of GdGaTi2O7 in the Temperature Range of 320-1000 K

L. T. Denisova, M. S. Molokeev, L. G. Chumilina, V. V. Ryabov & V. M. Denisov Physics of the Solid State

DOI: https://doi.org/10.1134/S1063783421040065

Titanate GdGaTi2O7 has been obtained from the initial oxides Gd2O3, Ga2O3, and TiO2 by the solid-state synthesis via annealing in air at temperatures of 1273 and 1573 K. The crystal structure of the titanate has been refined by X-ray diffraction. The high-temperature (320–1000 K) heat capacity of the compound has been measured by differential scanning calorimetry. Based on the experimental dependence Cp = f(T), the main thermodynamic functions of the titanate have been calculated.

Synthesis and Structural, Magnetic, and Thermal Properties of the Titanium-Doped Pb3Mn7O15 Compound

Sofronova, SN, Eremin, EV, Molokeev, MS, Mikhashenok, NV, Kartashev, AV PHYSICS OF THE SOLID STATE

DOI: https://doi.org/10.1134/S1063783421040223

The Pb3Mn7O15 crystals doped with titanium ions have been synthesized. The study of the structural properties has shown that titanium ions occupy positions in the interplane columns, which weakens the exchange coupling between the planes. Two anomalies in the temperature dependences of magnetization and heat capacity at 62 and 35 K have been found. It has been supposed that, at 62 K, the long-range magnetic order arises and, at 35 K, a spin-reorientation transition, as in the Pb3Mn7O15 compound, occurs.

Effect of Electron and Hole Doping on the Transport Characteristics of Chalcogenide Systems

Romanova, O. B.; Aplesnin, S. S.; Udod, L., V/ Physics Of The Solid State/

https://doi.org/10.1134/S1063783421050152

The electrical properties of the Ag0.01Mn0.99S and Tm0.01Mn0.99S semiconductor compounds and the Hall effect in them have been investigated in the temperature range of 80–400 K in a magnetic field of 12 kOe. Using the I–V characteristics, the conductivity mechanism depending on the doping type and concentration has been established. Upon substitution of silver for manganese, the Mott-type conductivity has been found, while substitution of thulium causes the ohmic conductivity. The mobility and type of carriers have been determined from the Hall constant data.

Synthesis and Structural and Magnetic Properties of the NaNiFe2(VO4)(3) Compound

Drokina, T., V; Velikanov, D. A.; Bayukov, O. A.; Molokeev, M. S.; Petrakovskii, G. A./ Physics Of The Solid State/

https://doi.org/10.1134/S1063783421060056

A new magnetic compound NaNiFe2(VO4)3 has been obtained by the solid-phase synthesis and studied by X-ray diffractometry, nuclear gamma resonance, and magnetometry. The crystal structure of multicomponent vanadate is described by a triclinic symmetry space group P1. The unit cell contains six nonequivalent mixed cationic positions occupied by different-valence ions of transition metals, iron Fe3+ and nickel Ni2+, which facilitates the implementation of a state with the local charge neutrality violation. In addition, two types of iron atom sites have been found, which have an oxygen environment in the form of octahedra and square pyramids with their nonequiprobable population by iron and nickel. The temperature and field dependences of the magnetization have been found to be typical of a paramagnet containing ferromagnetic clusters in a wide temperature range.

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