The Deformation Stimulated Luminescence in KCl, KBr and KI Crystals

Currently, strengthening of the intensity of luminescence in alkali halide crystals (AHC) at lattice symmetry lowering is discussed as a promising direction for the development of scintillation detectors. In this regard, for the study of anion excitons and radiation defects in the AHC anion sublattice at deformation, the crystals with the same sizes of cations and different sizes of anions were chosen. In the X-ray spectra of KCl at 10 K, the luminescence at 3.88 eV; 3.05 eV and 2.3 eV is clearly visible. The luminescence at 3.05 eV corresponds to the tunneling recharge [F*, H]. Luminescence at 3.88 eV is quenched in the region of thermal destruction of F'-centers and characterizes tunneling recharge of F', VK-centers. In KCl at 90 K, the luminescence of self-trapped excitons (STE) is completely absent. In KBr at deformation not only STE luminescence, but also deformation stimulated luminescence at 3.58 eV were recorded, the last one corresponds to tunneling recharge of F', VK-centers. In KI crystal at 10 K and 90 K at deformation, only STE luminescence is enhanced. There are no deformation luminescence bands in KI compares with KBr and KCl crystals

Computer Simulations of the Band Structure and Density of States of the Linear Chains of NaCl Ions

The authors thank Eugene Kotomin and V. Kuzovkov for fruitful discussions and valuable suggestions. A.I.P thanks A.Moskina for the technical assistance in preparation of the manuscript. A.I.P also gratefully acknowledges a project LZP-2018/1-0214 from the Latvian Council of Science for partial support.The paper presents the results of first-principles computer simulations of the band structure, the density of states, and the total energy of NaCl (NaCl, Na2Cl2, Na3Cl3, Na4Cl4, Na6Cl6) linear chains of atoms. Modelling of the specified characteristics is realised in the computer code Atomistix ToolKit combined with Virtual NanoLab. The total energy depends on the number of ions in the nanoobject under study, but practically does not depend on the geometric arrangement of ions.Latvian Council of Science LZP-2018/1-0214; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Electroplasma enrichment of natural diatomite

Method of electrohydraulic enrichment of natural diatomite from the Kazakhstan deposit as a multipurpose nanomaterial has been developed. Electrohydraulic method is based on separation of diatomite from the clay component under the influence of plasma energy arising in a short electric discharge. Complex study of enriched diatomite by spectral, X-ray diffraction (XRD), silicate (chemical) and thermal analysis methods was carried out. Independent methods of analysis applied show almost identical results for the degree of diatomite enrichment with silicon oxides (SiO2), being in the range of 78 - 80 %

Transport Properties of One-Dimensional van der Waals Heterostructures Based on Molybdenum Dichalcogenides

The transport properties of one-dimensional van der Waals nanodevices composed of carbon nanotubes (CNTs), hexagonal boron nitride (hBN) nanotubes, and molybdenum dichalcogenide (MoX2) nanotubes were investigated within the framework of density functional theory (DFT). It was found that in nanodevices based on MoS2(24,24) and MoTe2(24,24), the effect of resonant tunneling is suppressed due to electron–phonon scattering. This suppression arises from the fact that these materials are semiconductors with an indirect band gap, where phonon participation is required to conserve momentum during transitions between the valence and conduction bands. In contrast, nanodevices incorporating MoSe2(24,24), which possesses a direct band gap, exhibit resonant tunneling, as quasiparticles can tunnel between the valence and conduction bands without a change in momentum. It was demonstrated that the presence of vacancy defects in the CNT segment significantly degrades quasiparticle transport compared to Stone–Wales (SW) defects. Furthermore, it was revealed that resonant interactions between SW defects in MoTe2(24,24)–hBN(27,27)–CNT(24,24) nanodevices can enhance the differential conductance under certain voltages. These findings may be beneficial for the design and development of nanoscale diodes, back nanodiodes, and tunneling nanodiodes

Deformation-induced enhancement of Ex-emission in RbI and KI single crystals

Drastic changes in the spectra of X-ray luminescence have been detected in pure RbI and KI single crystals exposed to uniaxial elastic deformation at 85 K. The intensity of both the σ-component of self-trapped exciton (STE) emission (maxima at 4.2 and 3.9 eV in RbI and KI, respectively) and the co-called Ex-luminescence (peaked at 3.05 eV in RbI and at 3.1 eV in KI) linearly increases with relative degree of deformation up to ε ≈ 1 %. The similarity of the dependence I = f(ε) for both emissions confirms the intrinsic origin of the Ex-luminescence in KI and RbI. Using a KI:Tl crystal as an example, it has been shown that low-temperature uniaxial elastic deformation causes a reduction in the mean free path of anion excitons, and, in turn, increases the efficiency of their self-trapping at regular lattice sites and subsequent radiative decay of STEs