Physical properties of fluorides barium and calcium nanopowders produced by the pulsed electron beam evaporation method

The mesoporous nanocrystal powders BaF 2 and CaF 2 with a specific surface up to 34.8 and 88.7 sq.m/g, respectively, are produced by the pulsed electron beam evaporation method in vacuum. The influence of thermal annealing of nanoparticles on air in the range of temperature from 200 to 900°C on the size, morphology of particles and change of their magnetic and luminescent properties investigated have been investigared. The essential stoichiometric impurity (overage of metals) and significant growth in a specific surface of nanopowders (NP) BaF 2 and CaF 2 after annealing at the temperature of 200°C have been detected. It is established that the synthesized NP BaF 2 is a paramagnetic while initial material in the bulk state is diamagnetic. After annealing at 900°C appears the small ferromagnetic contribution at NP BaF 2 . Produced NP CaF 2 showed ferromagnetic behavior. In literature there is no information about the ferromagnetism of CaF 2 . Appearance of the ferromagnetic response can be explained with formation of structural and radiation defects (F-centers, etc.). The analysis of PCL and magnetization curves of samples BaF 2 and CaF 2 allows drawing conclusions about their connection. © Published under licence by IOP Publishing Ltd.The authors are grateful to Pryanichnikov S.V., a researcher of the shared equipment center “Ural” of the Institute of Metallurgy of the Ural division of RAS, for the X-ray phase analysis; to the researchers of the Institute of Electrophysics of the Ural division of RAS Demina T.M. for the texture analysis, Murzakayev A.M. and Timashenkova O.R. for the microscopic analysis, Spirina A.V. for the PCL analysis. This work has been carried out within the scope of government order No. 0389-2015-0026 and with partial support of RFBR project No. 18-08-00514. The magnetic measurements were carried out within the scope of government order under the topic MAGNIT, state registration No. AAAA-A18-118020290129-5

Multifrequency dial sensing of the atmospheric gaseous constituents using the first and second harmonics of a tunable CO2 laser radiation

The results of field measurements of concentration of some gaseous components of the atmosphere along the paths, in Sofia, Bulgaria, using a gas analyzer based on the use of a CO2 laser radiation frequency-doubled with ZnGeP2 monocrystals are presented. The gas analyzer is a traditional long path absorption meter. Radiation from the tunable CO2 laser of low pressure and from an additional He-Ne laser is directed to a colliminating hundredfold Gregori telescope with a 300 mm diameter of the principal mirror. The dimensions of the mirrors of a retroreflector 500 x 500 mm and a receiving telescope allow one to totally intercept the beam passed through the atmospheric layer under study and back

Properties of the amorphous-nanocrystalline Gd2O3 powder prepared by pulsed electron beam evaporation

An amorphous-nanocrystalline Gd2O3 powder with a specific surface area of 155 m2/g has been prepared using pulsed electron beam evaporation in vacuum. The nanopowder consists of 20- to 500-nm agglomerates formed by crystalline nanoparticles (3-12 nm in diameter) connected by amorphous-nanocrystalline strands. At room temperature, the Gd2O3 nanopowder exhibits a paramagnetic behavior. The phase transformations occurring in the powder have been investigated using differential scanning calorimetry and thermogravimetry (40-1400°C). The amorphous phase of the nanopowder is thermally stable up to a temperature of 1080°C. It has been found that the amorphous phase has an inhibitory effect on the temperature of the polymorphic transformation from the cubic phase into the monoclinic phase. It has been revealed that, compared with the microcrystalline powder, the Gd2O3 nanopowder is characterized by a complete quenching of photoluminescence. © 2013 Pleiades Publishing, Ltd

Improvement in steel smelting by studying melt behavior

Analysis shows that the disequilibrium of melts may be used to characterize metal quality and to optimize smelting technology. For the production of pipe steel by means of a superpowerful DSP-135 arc furnace, a ladle-furnace unit, a vacuum-treatment system, and a continuous-casting machine, the sources of melt disequilibrium are studied in relation to the properties of the final steel. That provides the basis for the development of parameters characterizing different stages of the process. The proposed improvements in smelting technology are shown to be very efficient. © 2013 Allerton Press, Inc

Site-selective luminescence of Eu3+ ions in silicate-tungstates with apatite and scheelite structures

The present work studies europium-ion spectroscopic features in solid solutions based on silicate-tungstates Ca2La6.8Eu1.2Si5.6W0.4O26.4 and Ca8Eu2Si3W3O26 microcrystalline powders with the crystal structure of silicate apatite and scheelite respectively. The spectroscopic features were studied by means of photoluminescence spectroscopy and X-ray excited luminescence at temperatures 4.6, 90 and 295 K. In Ca2La6.8Eu1.2Si5.6W0.4O26.4 only intensive luminescence was observed, which was characterized by a set of 5D0 → 7FJ dominant intraconfigurational transitions for Eu3+ ion. In Ca8Eu2Si3W3O26, both 5D0→ 7FJ intraconfigurational transitions for Eu3+ ion and wide 430 nm emission band corresponding to host self-trapped exciton (STE) emission are observed. This STE emission band is reabsorbed by the f – f absorption of Eu3+ ions by means of energy transfer from host to Eu3+. The asymmetry coefficient which characterizes the shape of the emission spectrum of Eu3+ ions strongly depends on the energy of exciting photons. The Eu3+ ion might occupy two nonequivalent crystallographic sites. Some features of this phenomenon were discussed. © 2022 The Author(s)State Task, (0397-2019-0002)Russian Foundation for Basic Research, РФФИ, (20-03-00851)Russian Academy of Sciences, РАНMinistry of Education and Science of the Russian Federation, Minobrnauka, (FEUZ-2020-0060)Russian Science Foundation, RSF, (21-12-00392)Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences, ISSC UB RASThe work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, project No. FEUZ-2020-0060 ) and RFBR (project No. 20-03-00851 ) and it is part of a State Task (No. 0397-2019-0002 ) for the Institute of Solid State Chemistry ( Ural Branch, Russian Academy of Sciences ). V.A.P. acknowledges partial support by Russian Science Found (Project No. 21-12-00392 ). Authors thank to Dr. I.D. Popov (Institute of Solid State Chemistry, UB RAS, Ekaterinburg, Russia) for editing the text of the manuscript

Photon avalanche in nanoluminophore obtained by REE silicate evaporation

A bulk phosphor composition Sr2Y6.8YbEr0.2Si6O26 was synthesized. A nanophosphorus in an amorphous state was obtained from this sample by the method of pulsed electron beam evaporation. The spectra of upconversion photoluminescence of bulk and nanosamples were studied. In the field of pumping power of nanosample with 78 mW laser radiation with a wavelength of 980 nm, there is a threshold population of energy levels Er3+. Laser radiation carries out resonant pumping of 4I13/2 → 4F9/2 transition. Then there is an intensive red radiation upon transition 4F9/2 → 4I15/2. A photon avalanche was found in the nanophosphore, at which the intensity of red radiation increases ∼80 times compared to the bulk phosphorus. © 202

Photo-Thermoelectric Effect at a Graphene Interface Junction

We investigate the optoelectronic response of a graphene interface junction, formed with bilayer and single-layer graphene, by photocurrent (PC) microscopy. We measure the polarity and amplitude of the PC while varying the Fermi level by tuning a gate voltage. These measurements show that the generation of PC is by a photo-thermoelectric effect. The PC displays a factor of ~10 increase at the cryogenic temperature as compared to room temperature. Assuming the thermoelectric power has a linear dependence on the temperature, the inferred graphene thermal conductivity from temperature dependent measurements has a T^{1.5} dependence below ~100 K, which agrees with recent theoretical predictions

SITE-SELECTIVE LUMINESCENCE OF SOLID SOLUTIONS BASED ON SILICATE-TUNGSTATES DOPED WITH Eu3+ IONS

Energy transfer processes and europium-ion spectroscopic manifestations in Ca2La6.8Eu1.2Si5.6W0.4O26.4 and Ca8Eu2Si3W3O26 solid solutions were studied using photolu-minescence spectroscopy and upon X-ray excitation.The work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, project No. FEUZ-2020-0060) and RFBR (project No. 20-03-00851)

LUMINESCENCE OF SOLID SOLUTIONS BASED ON SILICATE-GERMANATE WITH APATITE STRUCTURE DOPED WITH Eu3+ IONS

In this report, we have investigated energy transfer processes and europium impurity cen-ters spectroscopic manifestations in Ca2La6.8Eu1.2Si4.8Ge1.2O26 microcrystalline powder by means of photoluminescence (PL) spectroscopy and upon X-ray excitation. excitation.The work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, project FEUZ-2020-0060) and RFBR (project No. 20-03-00851)