Optical properties and structure particularities of LiNbO3 crystals grown from a boron-doped melt

A series of LiNbO3:B crystals was grown from the melt doped by boron. It is shown that LiNbO3:B crystals possess an increased resistance to optical damage. We have found changes according to Raman spectra confirming the ordering of Li+, Nb5+ cations and vacancies along the polar axis. The chemical interactions were studied in the system Li2O–B2O3–Nb2O5. Boron cations are unable to incorporate into a cation sublattice of LiNbO3, but they change the physic-chemical structure of a melt. It contributes to an increased structure and optical uniformity of LiNbO3:B.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

Research on the antiviral activity of water-soluble melanin from the pharmaceutical chaga mushroom (Inonotus obliquus) against influenza А virus subtypes H5N1, H3N2 and H1N1pdm09 in experiments in vitro

Introduction. Influenza A virus is the cause of epidemics and pandemics that severely affect the health and socioeconomic status of the world's population. The need to develop new methods of etiotropic therapy, and the increasing ability of viruses to counteract the antiviral drugs makes extremely relevant the search for new pharmacologically active substances and the subsequent study of their medicinal properties. The aim of the study is to conduct research into the antiviral properties of melanin obtained from the pharmaceutical chaga mushroom in relation to different subtypes of the influenza A virus. Materials and methods. A sample of water-soluble melanin from Inonotus obliquus obtained by alkaline hydrolysis and dried at 40C was tested for toxicity and antiviral activity. The commercial anti-influenza drug Tamiflu was used as a reference drug. Statistical processing of the obtained data was carried out according to the Spearman-Kerber method. Results. Inonotus obliquus melanin (sample 20-24) toxicity markers, such as a maximum tolerable concentration (MTC) of 237.0 g/mL, and a 50% cytotoxic concentration (CC50) of 153,45 g/mL were established for MDCK cell culture. The assessment of antiviral activity of test sample against three subtypes of the influenza A virus (H5N1, H3N2 and H1N1pdm09) demonstrated a decrease in the infectivity of the influenza virus by 2.53.5 lg with 50% virus-inhibiting concentrations (IC50) of 1.559.52 g/mL. Based on the obtained values of CC50 and IC50, the selectivity indices (SI) of the sample were calculated, characterizing its prospects for further research. Conclusions. Melanin obtained from the pharmaceutical chaga mushroom showed the highest activity against the strain of the human pandemic influenza virus A/California/04/2009 (H1N1)pdm09, caused a decrease in its infectivity by 3.5 lg and had an IC50 of 1.6 g/ml. The obtained results indicate the prospects for creating an antiviral drug based on Inonotus obliquus melanins against the influenza virus

Radiation Modification of Optical Characteristics of LiNbO3:Zn and LiNbO3:Mg Crystals

The modification of the optical characteristics of LiNbO3:Zn and LiNbO3:Mg crystals grown by the Czochralski method was investigated using β and γ radiation. The photorefractive effect was found to be inhibited by ionizing radiation in the LiNbO3:Zn ([ZnO] ≈ 2.1 mol%) crystal, which belonged to a below-threshold concentration range. The inhibition was attributed to a stepwise radiation annealing of charged defects. Ionizing radiation increased the general optical uniformity of above-threshold crystals LiNbO3:Zn ([ZnO] ≈ 5.9 mol%) and LiNbO3:Mg([MgO] ≈ 5.6 mol%). In addition, we determined that radiation annealing substantially influenced photorefraction dynamics in lightly doped LiNbO3:Zn ([ZnO] ≈ 0.1 mol%) crystals, which widens their application areas

Some Optical Properties of LiNbO₃:Gd³⁺(0.003):Mg²⁺(0.65 wt %) Single Crystal: A Promising Material for Laser Radiation Conversion

A nonlinear optical double-doped single-crystal LiNbO3:Gd:Mg (Gd concentration is 0.003, Mg—0.65 wt % in the crystal) has been researched by several optical methods: laser conoscopy, photoinduced light scattering (PILS), optical spectroscopy, and Raman scattering. The crystal has been shown to have no photorefraction effect and a high optical uniformity. Fine features of the crystal structure have been studied via Raman spectra. Spectra have been registered in the first and second orders, they have been excited by visible (532 nm) and near-IR (785 nm) lasers. Registered Raman spectra have the fundamental vibrations of the crystal lattice of the A1(TO,LO)- and E(TO,LO)-type symmetry located in the range of 150–900 cm−1. A number of low-intensity Raman bands in the 900–2000 cm−1 region have been determined to correspond to the second-order Raman spectrum. These bands are polarized and appear only in certain polarization-scattering geometries. They appear in the spectrum excited by visible radiation, but their number and intensity are much lower than those excited by near-IR lasers. Oxygen-octahedral MeO6 clusters in our case can contain Li, Nb, Gd, or Mg in the Me site. The clusters in the LiNbO3:Gd:Mg crystal structure are slightly distorted compared with similar clusters in the nominally pure LiNbO3 crystal. It has been established that the value R = [Li]/[Nb] in the studied crystal is ≈ 1. Such a ratio usually characterizes a nominally pure stoichiometric crystal

Growing, Structure and Optical Properties of LiNbO₃:B Crystals, a Material for Laser Radiation Transformation

Physical and chemical properties have been studied in lithium niobate (LiNbO3, LN) crystals grown by Czochralski from a boron doped melt. Optical uniformity and optical damage resistance of LiNbO3:B crystals have been compared with control crystals of nominally pure congruent (CLN) and near-stoichiometric (NSLN K2O) composition. LiNbO3:B crystals structure has been studied. Studied LiNbO3:B crystals have been grown from differently synthesized charges. The charges have been synthesized from a mixture Nb2O5:B-Li2CO3 using homogeneously doped Nb2O5:B precursor (sample 1, (B) = 0.0034 wt% in the charge) and by a direct solid phase synthesis from Nb2O5-Li2CO3-H3BO3 mixture (sample 2, (B) = 0.0079 wt% in the charge). Only traces of boron (10−5–10−4 wt%) have been detected in the samples. We have established that concentration of anti-site defects NbLi is lower in both LiNbO3:B than in CLN crystals. XRD analysis has confirmed that B3+ cations localize in faces of tetrahedral voids O4 of LN structure. The voids act as buffers at the anion sublattice distortion. Sample 1 has been shown to have a structure closer to NSLN K2O crystal than sample 2. We have also shown that the chemical purity of LN crystal increases compared to the melt purity because boron creates strong compounds with impurities in the melt system Li2O-Nb2O5-B2O3. Metals impurities thus stay in the melt and do not transfer to the crystal