Green,blue, red,near-infrared up-conversion luminescence of Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Tm<Superscript>3+</Superscript> co-doped YVO<Subscript>4</Subscript> nanoparticles

YVO₄:Yb³⁺,Er³⁺; YVO₄:Yb³⁺,Tm³⁺; and YVO₄:Yb³⁺,Er³⁺,Tm³⁺ were all synthesized via sol-gel method with a subsequent thermal treatment. Specifically, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ phosphors were prepared with different annealing temperatures to study the influence of temperature. The transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescent (PL) spectrofluorometer were used to investigate the morphology, crystal structure, and up-conversion luminescent properties of all samples. In summary, all samples were granular-like nanoparticles and well crystallized with the same tetragonal phase as YVO₄. Under the irradiation at 980 nm, YVO₄:Yb³⁺,Er³⁺ phosphors can generate green emission at 525 and 553 nm and red emission at 657 nm, while YVO₄:Yb³⁺,Tm³⁺ phosphors can generate blue emission at 476 nm, red emission at 648 nm, and near-infrared emission at 800 nm. Notably, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ samples can exhibit green emission, blue emission, red emission, and near-infrared emission at the same time, which might endow the as-prepared samples with potential applications in many fields, such as luminous paint, infrared detection, and biological label.     

Neutron single-particle structure of <Superscript>48</Superscript>Ca, <Superscript>50</Superscript>Ti, <Superscript>52</Superscript>Cr, <Superscript>54</Superscript>Fe,and <Superscript>56</Superscript>Ni nuclei

The change in the neutron single-particle structure of (1f?2p)-shell magic nuclei near the Fermi energy with an increase in the number of protons in the 1f _7/2 subshell from 0 for ⁴⁸Ca to 8 for ⁵⁶Ni has been investigated. Good agreement of the experimental and estimated values of the single-particle energies E _nlj of the bound states of neutrons in these nuclei with the results of calculations within the dispersive optical model is obtained.     

Nuclear level densities in <Superscript>47</Superscript>V, <Superscript>48</Superscript>V, <Superscript>49</Superscript>V, <Superscript>53</Superscript>Mn,and <Superscript>54</Superscript>Mn from neutron evaporation spectra

The spectra of neutrons from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, and ⁵⁴Cr nuclei were measured in the proton-energy range 7–11 MeV. The measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). Owing to a high resolution and a high stability of the time-of-flight spectrometer used, low-lying discrete levels could be identified reliably along with a continuum section of neutron spectra. An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The relevant calculations were performed by using the exact formalism of Hauser-Feshbach statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for the nuclear level density. The nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, and ⁵⁴Mn were determined along with their energy dependences and model parameters. The results are discussed together with available experimental data and recommendations of model systematics.     

Nuclear deformation and the two-neutrino double- β decay in <Superscript>124, 126</Superscript>Xe , <Superscript>128, 130</Superscript>Te , <Superscript>130, 132</Superscript>Ba and <Superscript>150</Superscript>Nd isotopes

The two-neutrino double-beta decay of ^{124, 126}Xe , ^{128, 130}Te , ^{130, 132}Ba and ¹⁵⁰Nd isotopes is studied in the Projected Hartree-Fock-Bogoliubov (PHFB) model. Theoretical 2ν β^-β^- half-lives of ^{128, 130}Te , and ¹⁵⁰Nd isotopes, and 2ν β⁺β⁺ , 2ν β⁺ EC and 2ν ECEC for ^{124, 126}Xe and ^{130, 132}Ba nuclei are presented. Calculated quadrupolar transition probabilities B(E2 : 0⁺ → 2⁺) , static quadrupole moments and g -factors in the parent and daughter nuclei reproduce the experimental information, validating the reliability of the model wave functions. The anticorrelation between nuclear deformation and the nuclear transition matrix element M _2ν is confirmed.     

Synthesis,sintering, and conductivity of Mn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

Studies on the sintering of manganese pyrovanadate depending on the temperature and the crystallite size show that we are prevented from obtaining a bulk ceramic sample by the anisotropic growth of grains. Investigation of the electrical properties of Mn₂V₂O₇ in the temperature range of 250–800°C reveals the activation energy at which bulk conductivity is 0.62 eV.     

Synthesis,characterization, and thermal stability of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>/CR-Ag multilayered nanostructures

The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO₂ particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO₂/TiO₂ particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C.     

Peculiarities of magnetic,galvanomagnetic, elastic,and magnetoelastic properties of Eu<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript>

Magnetic, elastic, magnetoelastic, transport, and magnetotransport properties of the Eu_0.55Sr_0.45MnO₃ ceramics have been studied. A break was detected in the temperature dependence of electrical resistivity ρ(T) near the temperature of the magnetic phase transformation (41 K), with the material remaining an insulator down to the lowest measurement temperature reached (ρ=10⁶ Ω cm at 4.2 K). In the interval 4.2≤T≤50 K, the isotherms of the magnetization, volume magnetostriction, and ρ were observed to undergo jumps at the critical field H_C1, which decreases with increasing T. For 50≤T≤120 K, the jumps in the above curves persist, but the pattern of the curves changes and H_C1 grows with increasing T. The magnetoresistance Δρ/ρ = (ρ _H ?ρ_H=0)/ρ _H is positive for H<H_C1 and passes through a maximum at 41 K, where Δρ/ρ = 6%. For H>H_C1, the magnetoresistance is negative, passes through a minimum near 41 K, and reaches a colossal value of 3×10⁵ % at H=45 kOe. The volume magnetostriction is negative and attains a giant value of 4.5×10^?4atH=45 kOe. The observed properties are assigned to the existence of three phases in Eu_0.55Sr_0.45MnO₃, namely, a ferromagnetic (FM) phase, in which carriers are concentrated because of the gain in s-d exchange energy, and two antiferromagnetic (AFM) phases of the A and CE types. Their fractional volumes at low temperatures were estimated to be as follows: ～3% of the sample volume is occupied by the FM phase; ～67%, by the CE-type AFM phase; and ～30%, by the A-type AFM phase.     

Synthesis,characterization, and cell performance of Li<Subscript>0.5</Subscript>FeV<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

A Li_0.5FeV_1.5O₄ sample was synthesized using sol-gel route. The X-ray diffraction study indicates formation of spinel phase (with Fd3m space group) for this sample. LiO₄, LiO₆, and V-O bonds were identified from the Raman spectrum, while LiO₄ and Fe-O bonds were identified from the FTIR spectrum of this sample phase. The FESEM study indicates formation of inhomogeneous grains. The surface area of 74.39 m²/g was estimated from the Brunauer-Emmett-Teller (BET) surface area analysis technique. The cyclic voltammetry study of Li_0.5FeV_1.5O₄ indicates an anodic peak at 2.1 V while a cathodic peak at 1.98 V. The charge-discharge study exhibits two voltage plateaus respectively at 2.1 and at 4 V. Stable electrochemical capacity of 40 mAh/g for Li_0.5FeV_1.5O₄ was found for 30 cycles. The electrochemical impedance spectroscopy study indicates smaller bulk resistance and higher ionic diffusion, i.e., less Warburg impedance for this phase. An energy density of 89 Wh/kg, a power density of 33 W/kg, and a 90% Coulombic efficiency was achieved with relatively good cyclic stability from Li_0.5FeV_1.5O₄.     

Electronic Structure,Optical Properties,and Pressure Behavior of the CdB<Subscript>4</Subscript>O<Subscript>7</Subscript> and HgB<Subscript>4</Subscript>O<Subscript>7</Subscript> Compounds

Ab initio calculations of the structural, electronic, and optical properties of the CdB₄O₇ and HgB₄O₇ tetraborate compounds in three structural modifications with the Pbca, Cmcm, and Pmn2₁ symmetry have been performed in the framework of the density functional theory using the VASP package. The calculations of the electronic band structure showed that these compounds in all the investigated modifications are dielectrics with a band gap of 2–4 eV. The calculation of the structural properties of the tetraborates under pressure showed that the phase transition between the Pbca and Pmn2₁ structures in cadmium and mercury tetraborates occurs under pressures of 4.8 and 4.7 GPa, respectively.     

Structural,elastic, electronic,optical and thermal properties of c-SiGe<Subscript>2</Subscript>N<Subscript>4</Subscript>

We have investigated the structural, elastic, electronic, optical and thermal properties of c-SiGe₂N₄ by using the ultrasoft pseudopotential density functional method within the generalized gradient approximation. The calculated structural parameters, including the lattice constant, the internal free parameter, the bulk modulus and its pressure derivative are in agreement with the available data. The independent elastic constants and their pressure dependence, calculated using the static finite strain technique, satisfy the requirement of mechanical stability, indicating that c-SiGe₂N₄ compound could be stable. We derive the shear modulus, Young’s modulus, Poisson’s ratio and Lamé’s coefficients for ideal polycrystalline c-SiGe₂N₄ aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimate the Debye temperature of this compound from the average sound velocity. Band structure, density of states, Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, in order to understand the optical properties of c-SiGe₂N₄, the dielectric function, refractive index, extinction coefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermal effects on some macroscopic properties of c-SiGe₂N₄ are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have obtained successfully the variations of the primitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K. For the first time, the numerical estimates of the elastic constants and related parameters, and the thermal properties are performed for c-SiGe₂N₄.     

Band interaction in <Superscript>162</Superscript>Dy, <Superscript>168</Superscript>Er,and <Superscript>172</Superscript>Yb

Coriolis interaction between levels of two rotational bands in ¹⁷²Yb with K ^π = 2⁺ and 3⁺ and in ¹⁶⁸Er between levels with K ^π = 0^?, 1^?, and 2^? is studied. The values of the interaction parameters are obtained. The mutual influence of two bands in ¹⁶²Dy with ΔK = 2, K _i ^π = 0 ₂ ⁺ and 2 ₁ ⁺ due to Coriolis interaction is demonstrated.     

Genesis,structural, and transport properties of La<Subscript>2</Subscript>Mo<Subscript>2-x</Subscript>W<Subscript>x</Subscript>O<Subscript>9</Subscript> prepared via mechanochemical activation

Fast oxide-ion conductors La₂Mo_2-xW_xO₉ (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La₂Mo_2-xW_xO₉ genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10^?3 S/cm at 630 °C) at temperatures below 650 °C.     

The phase transition,hygroscopicity, and thermal expansion properties of Yb_2-xAl_xMo₃O₁₂

Materials with the formula Yb 2-xAlxMo3O12(x =0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8) were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffrac- tion, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3O12 solid solutions crystallize in a single monoclinic phase for 1.7 ≤ x ≤ 2.0 and in a single orthorhombic phase for 0.0 ≤ x ≤ 0.4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhombic phase transition temperature of Al2Mo3O12 can be reduced by partial substitution of Al 3+ by Yb3+, and the Yb2-x AlxMo3O12 (0.0 < x ≤ 2.0) materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of Al3+ for Yb3+ in Yb2Mo3O12 decreases its hygroscopicity, and the linear thermal expansion co- efficients after complete removal of water species are measured to be 9.1×10 6 /K, 5.5×10 6 /K, 5.74×10 6 /K, and 9.5 × 10 6 /K for Yb1.8 Al0.2 (MoO4)3 , Yb1.6Al0.4 (MoO4 )3, Yb0.4 Al1.6 (MoO4)3 , and Yb 0.2Al1.8 (MoO4)3 , respectively.     

Structural,magnetic, and magnetothermal properties of the Tb<Subscript>0.3</Subscript>Dy<Subscript>0.7</Subscript>Co<Subscript>2</Subscript> compound

A complex investigation of the structural, magnetic, and magnetothermal properties of the Tb_0.3Dy_0.7Co₂ compound synthesized with the use of high-purity rare-earth metals has been performed. The phase composition has been controlled using the X-ray structural analysis, and the topology of the alloy surface has been investigated using atomic-force microscopy. It has been established that the Tb_0.3Dy_0.7Co₂ compound is single-phase, while the samples selected for measurements possess a clearly pronounced texture. The magnetization has been measured using a vibrating-sample magnetometer in the fields up to 100 kOe in a temperature range from 4.2 to 200 K. The Curie temperature of the compound is 170 K. The data on the temperature dependence of heat capacity of Tb_0.3Dy_0.7Co₂ have been obtained. The magnetocaloric effect ΔT has been measured by a direct method in the fields up to 18 kOe applied both along and perpendicularly to the texture axis. The anisotropic behavior of the magnitude ΔT for this compound, which possesses the cubic structure, has been found. The maximum value of the magnetocaloric effect ΔT = 2.3 K (ΔH = 18 kOe) has been observed upon applying the magnetic field along the texture axis.     

Comparison of halo of <Superscript>11</Superscript>Be, <Superscript>15</Superscript>C,and <Superscript>19</Superscript>C

We have compared the halo of ¹¹Be, ¹⁵C, and ¹⁹C nuclei by analyzing the one-neutron stripping reaction data on the Be target at 60-, 54-, and 57-MeV/A beam energies, respectively, within the framework of the eikonal approximation approach. The determination of effective range through the comparison of the total cross section data and prediction has revealed that the halo of ¹⁹C is the well developed, while that of ¹⁵C is the least and that of ¹¹Be lies in between these two. The longitudinal momentum distribution data also strengthen these observations. The text was submitted by the authors in English.     

Controlled-synthesis,characterization, and magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanostructures

Fe₃O₄ nanostructures with different morphologies, including uniform nanoparticles, nanorods and nanowire bundles, have been successfully synthesized via a facile hydrothermal route. Based on the observation of TEM images, the growth mechanism of one-dimensional Fe₃O₄ nanostructures is in accordance with Ostwald ripening process. From the hysteresis loops of as-prepared Fe₃O₄ products, we found that the morphology has great influence on the magnetic properties. The uniform Fe₃O₄ nanoparticles have higher saturation magnetization and lower coercivity than that of Fe₃O₄ nanorods and nanowires bundles. These phenomena attribute to the high shape anisotropy of nanorods and nanowire bundles, which prevent them from magnetizing in directions other than along their easy magnetic axes. PACS 81.07.-b; 75.50.Bb; 75.30.Gw; 81.10.Dn; 81.16.Be     

Structural,dielectric, electrical and piezoelectric properties of Ba<Subscript>4</Subscript>SrRTi<Subscript>3</Subscript>V<Subscript>7</Subscript>O<Subscript>30</Subscript> (R=Sm,Dy) ceramics

Polycrystalline samples of Ba₄SrRTi₃V₇O₃₀ (R=Sm and Dy), members of the tungsten-bronze family, were prepared using a high-temperature, solid-state reaction technique and studied their electrical properties (using complex impedance spectroscopy) in a wide range of temperature (31–500°C) and frequency (1 kHz-1 MHz). Preliminary structural (XRD) analyses of these compounds show the formation of single-phase, orthorhombic structures at room temperature. The scanning electron micrographs (SEM) provided information on the quality of the samples and uniform distribution of grains over the entire surface of the samples. Detailed studies of the dielectric properties suggest that they have undergone ferroelectric-paraelectric phase transition well above the room temperatures (i.e., 432 and 355°C for R= Sm and Dy, respectively, at frequency 100 kHz). Measurements of electrical conductivity (ac and dc) as a function of temperature suggest that the compounds have semiconducting properties much above the room temperature, with negative temperature coefficient of resistance (NTCR) behavior. The existence of ferroelectricity in these compounds was confirmed from a polarization study.      

Structural,optical, and thermal properties of MAX-phase Cr<Subscript>2</Subscript>AlB<Subscript>2</Subscript>

First-principles calculations of the structural, optical, and thermal properties of Cr₂AlB₂ are performed using the pseudopotential plane-wave method within the generalized gradient approximation (GGA). Calculation of the elastic constant and phonon dispersion indicates that Cr₂AlB₂ is mechanically and thermodynamically stable. Analysis of the band structure and density of states indicates that Cr₂AlB₂ is metallic. The thermal properties under increasing temperature and pressure are investigated using the quasi-harmonic Debye model. The results show that anharmonic effects on Cr₂AlB₂ are important at low temperature and high pressure. The calculated equilibrium primitive cell volume is 95.91 Å3 at T = 300 K, P = 0 GPa. The ability of Cr₂AlB₂ to resist volume changes becomes weaker with increasing temperature and stronger with increasing pressure. Analysis of optical properties of Cr₂AlB₂ shows that the static dielectric function of Cr₂AlB₂ is 53.1, and the refractive index n ₀ is 7.3. If the incident light has a frequency exceeding 16.09 eV, which is the plasma frequency of Cr₂AlB₂, Cr₂AlB₂ changes from metallic to dielectric material.     

Synthesis,crystal structure,Hirshfeld surface analysis,and vibrational and DFT investigation of [C<Subscript>6</Subscript>H<Subscript>10</Subscript>(NH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>3</Subscript>CuBr<Subscript>4</Subscript>.3Br

Single crystal of a new organic–inorganic hybrid material [C₆H₁₀(NH₃)₂]₃CuBr₄.3Br was synthesized by the slow evaporation method at room temperature and characterized by X-ray diffraction, FTIR, Raman spectroscopy, UV–Vis, dielectric measurements, and Hirschfield surface analysis. The title compound crystallizes in trigonal system \( P\overline{3} \).The crystal packing is governed by the N-H…Br and non-classical C-H…Br hydrogen-bonding interactions between the 1, 2-diamoniumcyclohexane cations, the tetrahedral [CuBr₄]^3? anions, and the isolated ion Br^?. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra, and optical properties of the investigated molecule in the ground state. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The optical properties were investigated by optical absorption and show two bands at 260 and 305 nm.