Magnesium cations as templates for the self-assembly of supramolecular luminescent {Mg@[B18φ34-35]}-clusters.

Solvothermal reaction of magnesium nitrate and boron oxide in N,N-dimethylformamide produced a number of particularly complex supramolecular magnesium borates. Five topologically different types of negatively charged {Mg@[B18φ34-35]}-clusters, φ = O, OH, were observed with the magnesium cation as a core and octadecaborate anions as shells. The clusters assemble via common borate polyhedra forming 1D chains, a 2D mesoporous layer, and 3D mesoporous frameworks with an effective channel width of up to 16 Å. Topological analysis of the clusters in combination with the modular crystallography approach indicates that numerous new functional materials can be obtained by varying their assembly mode. At least one compound containing such clusters exhibits a very strong luminescence.

Two distinct mechanisms of flavoprotein spectral tuning revealed by low-temperature and time-dependent spectroscopy.

Flavins such as flavin mononucleotide or flavin adenine dinucleotide are bound by diverse proteins, yet have very similar spectra when in the oxidized state. Recently, we developed new variants of flavin-binding protein CagFbFP exhibiting notable blue (Q148V) or red (I52V A85Q) shifts of fluorescence emission maxima. Here, we use time-resolved and low-temperature spectroscopy to show that whereas the chromophore environment is static in Q148V, an additional protein-flavin hydrogen bond is formed upon photoexcitation in the I52V A85Q variant. Consequently, in Q148V, excitation, emission, and phosphorescence spectra are shifted, whereas in I52V A85Q, excitation and low-temperature phosphorescence spectra are relatively unchanged, while emission spectrum is altered. We also determine the x-ray structures of the two variants to reveal the flavin environment and complement the spectroscopy data. Our findings illustrate two distinct color-tuning mechanisms of flavin-binding proteins and could be helpful for the engineering of new variants with improved optical properties.

In situ doping of epitaxial diamond with germanium by microwave plasma CVD in GeH4-CH4-H2 mixtures with optical emission spectroscopy monitoring.

We report the growth of Ge-doped homoepitaxial diamond films by microwave plasma CVD in GeH4-CH4-H2 gas mixtures at moderate pressures (70-100 Torr). Optical emission spectroscopy was used to monitor Ge, H, and C2 species in the plasma at different process parameters, and trends for intensities of those radicals, gas temperature, and excitation temperature, with variations of GeH4 or CH4 precursor concentrations, were investigated. The film deposited on (111)-oriented single crystal diamond substrates in a high growth rate regime revealed a strong emission of a germanium-vacancy (GeV) color center with a zero-phonon line at ≈604 nm wavelength in photoluminescence (PL) spectra, confirming the successful doping. The observed PL shift for the GeV defect is caused by stress in the films, as evidenced and quantified by Raman spectra. These results suggest that in situ doping with Ge using a GeH4 precursor is a convenient method of controlling the formation of GeV centers in epitaxial diamond films for photonic applications.

Phase Relations in the Ln2O3-Cr2O3-B2O3 (Ln = Gd-Lu) Ternary Oxide Systems.

In this work, isothermal sections of the Ln2O3-Cr2O3-B2O3 (Ln = Gd-Lu) ternary oxide systems at 900, 1000, and 1100 °C were constructed by determining the phase relations by using a powder X-ray diffraction technique. As a result, these systems were divided into subsidiary subsystems. Two types of double borates, LnCr3(BO3)4 (Ln = Gd-Er) and LnCr(BO3)2 (Ln = Ho-Lu), were observed in the investigated systems. Regions of phase stability for LnCr3(BO3)4 and LnCr(BO3)2 were determined. It was shown that the LnCr3(BO3)4 compounds crystallized in rhombohedral and monoclinic polytype modifications up to 1100 °C; above this temperature and up to the melting points, the monoclinic modification was predominantly formed. The LnCr3(BO3)4 (Ln = Gd-Er) and LnCr(BO3)2 (Ln = Ho-Lu) compounds were characterized by using a powder X-ray diffraction method and thermal analysis.

Manganese Luminescent Centers of Different Valence in Yttrium Aluminum Borate Crystals.

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe−Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.

UV Light Irradiation Effects in P-Doped Diamonds: Total Content Determination of Phosphorus Donors.

Upon the UV light irradiation of single-crystal diamonds doped with phosphorus, several effects have been observed. The integral intensity of phosphorus lines in FTIR absorption spectra under UV radiation was increased. A saturation effect depending on the power of the laser radiation was demonstrated. Narrowing of the phosphorus lines, as well as the redistribution of the intensities in their doublets caused by the Jahn-Teller distortion of the donor ground state, was observed. It was found that these effects are associated with the decompensation of the phosphorus donors. An easy, fast, sensitive, and nondestructive, fully optical method for the determination of the total phosphorus donor's concentration in semiconducting diamonds, as well as its compensation ratio, was proposed.

Observation of the hyperfine structure and anticrossings of hyperfine levels in the luminescence spectra of LiYF4:Ho3.

Resolved hyperfine structure and narrow inhomogeneously broadened lines in the optical spectra of a rare-earth-doped crystal are favorable for the implementation of various sensors. Here, a well-resolved hyperfine structure in the photoluminescence spectra of LiYF4:Ho single crystals and the anticrossings of hyperfine levels in a magnetic field are demonstrated using a self-made setup based on a Bruker 125HR high-resolution Fourier spectrometer. This is the first observation of the resolved hyperfine structure and anticrossing hyperfine levels in the luminescence spectra of a crystal. The narrowest spectral linewidth is only 0.0022 cm-1. This fact together with a large value of the magnetic g factor of several crystal-field states creates prerequisites for developing magnetic field sensors, which can be in demand in modern quantum information technology devices operating at low temperatures. Very small random lattice strains characterizing the quality of a crystal can be detected using anticrossing points.

Risk of colloidal and pseudo-colloidal transport of actinides in nitrate contaminated groundwater near a radioactive waste repository after bioremediation.

The possible role of biogeochemical processes in the transport of colloidal and pseudo-colloidal U, Np, and Pu during bioremediation of radionuclide- and nitrate-contaminated groundwater was investigated. In two laboratory experiments with water samples taken from contaminated aquifers before and post bioremediation, we found that microbial processes could cause clayed, ferruginous, and actinide colloids to coagulate. The main mechanisms are biogenic insoluble ferrous iron species formations (goethite, pyrrhotite, siderite, troilite, and ferrihydrite), the aggregation of clay particles by microbial metabolites, and the immobilization of actinides in the bacterial cells, large polymers, and iron and clayed sediments. This process decreases the risk of colloidal and pseudo-colloidal transport of actinides.

Biogeochemical Factors of Cs, Sr, U, Pu Immobilization in Bottom Sediments of the Upa River, Located in the Zone of Chernobyl Accident.

Laboratory modeling of Cs, Sr, U, Pu immobilization by phytoplankton of the river Upa, affected after the Chernobyl accident, has been carried out. Certain conditions are selected for strong fixation of radionuclides in bottom sediments due to biogeochemical processes. The process of radionuclide removal from the water phase via precipitation was based on their accumulation by phytoplankton, stimulated by nitrogen and phosphorus sources. After eight days of stimulation, planktonic phototrophic biomass, dominated by cyanobacteria of the genus Planktothrix, appears in the water sample. The effectiveness of U, Pu and Sr purification via their transfer to bottom sediment was observed within one month. The addition of ammonium sulfate and phosphate (Ammophos) led to the activation of sulfate- and iron-reducing bacteria of the genera Desulfobacterota, Desulfotomaculum, Desulfosporomusa, Desulfosporosinus, Thermodesulfobium, Thiomonas, Thiobacillus, Sulfuritallea, Pseudomonas, which form sulphide ferrous precipitates such as pyrite, wurtzite, hydrotroillite, etc., in anaerobic bottom sediments. The biogenic mineral composition of the sediments obtained under laboratory conditions was verified via thermodynamic modeling.

Bio-zeolite use for metal removal from copper-containing synthetic effluents.

The adsorption capacity of biologically modified zeolite with respect to copper-containing effluents (Cu(II)-Fe(III), Cu(II)-Fe(III)-Ni(II), Cu(II)-Fe(II)-Zn(II), and Cu(II)-Fe(II)-Ni(II)-Zn(II)) has been investigated in order to apply it for industrial effluents treatment. Obtained bio-zeolite was characterized using neutron activation analysis, confocal laser scanning microscopy, and scanning electron microscopy. The efficiency of metal ions removal was determined as a function of pH, copper concentration, time, and temperature. The metal sorption in analyzed systems showed to be pH-dependent. The equilibrium adsorption data were interpreted using Freundlich and Langmuir isotherms and the adsorption mechanism was investigated by kinetic studies. The sorption of Cu(II) and Zn(II) fitted well pseudo-first and pseudo-second-order models, while Ni(II) sorption was better described by the Elovich model. The thermodynamic parameters, ∆G°, ∆H°, and ∆S were evaluated to understand the nature of the sorption process. Obtained results show that bio-zeolite is of interest for heavy metal ions removal from industrial effluents. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40201-021-00694-x.

Investigation of materials for reactive permeable barrier in removing cadmium and chromium(VI) from aquifer near a solid domestic waste landfill.

The sorption characteristics of raw and biofilm-coated materials: vermiculite, lightweight expanded clay aggregate (LECA), perlite, zeolite, and shungite toward Cd and Cr(VI) ions were investigated to evaluate the possibility of their use as filtration barrier in the aquifer near a solid domestic waste landfill. The effectiveness of Cr(VI) removal by the raw materials changed in the following order: shungite > zeolite > perlite > vermiculite > LECA and for Cd: zeolite > shungite > vermiculite > perlite > LECA. After biofilm formation on the surface of the materials, the sorption capacity increased in some (perlite, LECA), while in others (zeolite) it was reduced. Four kinetic models were used to describe the experimental data. Mechanisms of metal removal were proposed: for Cr(VI), a characteristic combination of sorption processes was suggested, while the removal of Cd ions could occur by ion exchange and by complexation on the surface of the sorbent. Cr(VI) reduction by living bacterial cells forming a biofilm on the sorbent surface was assessed.

Selective metal removal from chromium-containing synthetic effluents using Shewanella xiamenensis biofilm supported on zeolite.

A scheme of selective removal of metal ions from chromium-containing synthetic solutions with the following chemical composition, Cr (VI)-Fe (III), Cr (VI)-Fe (III)-Ni (II), Cr (VI)-Fe (III)-Ni (II)-Zn (II), and Cr (VI)-Fe (III)-Ni (II)-Zn (II)-Cu (II)) by Shewanella xiamenensis biofilm immobilized on a zeolite support, was proposed. Three biological processes, biosorption, bioaccumulation, and longtime bioreduction, were applied for metal removal. The process of Zn (II), Ni (II), and Cu (II) showed to be pH dependent. The maximum removal of Ni (II) was achieved during a 1-hour biosorption process at pH 5.0-6.0, of Zn (II) at pH 5.0, and of Cu (II) at pH 3.0. Chromium (VI) and Fe (III) ions were more efficiently removed by bioaccumulation. Chromium (VI) removal in the studied systems varied from 16.4% to 34.8 and of iron from 55.8 to 94.6%. In a long-term bioreduction experiment, it was possible to achieve complete reduction of Cr (VI) to Cr (III) ions by Shewanella xiamenensis in 42 days and by Shewanella xiamenensis biofilm on zeolite in 35 days. Shewanella oneidensis can be effectively used to remove metal ions from chemically complex effluents.

Data on vibrational spectra of the langasites Ln3CrGe3Be2O14 (Ln = La, Pr, Nd) and ab initio calculations.

In "Lattice dynamics and structure of the new langasites Ln3CrGe3Be2O14 (Ln = La, Pr, Nd): vibrational spectra and ab initio calculations" [1], experimental and calculated results on lattice dynamics of the recently discovered new compounds La3CrGe3Be2O14, Pr3CrGe3Be2O14, and Nd3CrGe3Be2O14 are reported. These compounds belong to the langasite series and constitute a new class of low-dimensional antiferromagnets. The data presented in this article includes IR diffuse transmission spectra of powder samples of Ln3CrGe3Be2O14 (Ln = La, Pr, Nd) registered at room temperature with a Bruker 125HR Fourier spectrometer, Raman spectra taken in the backscattering geometry (also at room temperature) with a triple monochromator using the line 514, 5 nm of an argon laser as an excitation, results of the DFT calculations with the B3LYP and PBE0 hybrid functionals on the optimized crystal structures, eigenfrequencies and eigenvectors of the normal vibrational modes. These data can be used to analyse electron-phonon interaction and multiferroic properties of the new langasites and to compare the lattice dynamics of different langasites. The dataset is available on mendeley data public repository at https://doi.org/10.17632/32grbb4p82.1.

FTIR study of thermally induced magnetostructural transitions in breathing crystals.

"Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled clusters within the polymeric chains. Owing to an interplay of exchange interaction between copper(II) and nitroxide spins and Jahn-Teller nature of copper(II) complex, the breathing crystals demonstrate thermally and light-induced magnetostructural transitions in many aspects similar to the classical spin crossover. Herewith, we report the first application of variable temperature (VT) far/mid Fourier transform infrared (FTIR) spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR study was aimed toward clarification of the transitions mechanism previously debated on the basis of superconducting quantum interference device, X-ray diffraction, and electron paramagnetic resonance data. VT-FTIR showed the onset of new vibrational bands during phase transitions occurring at the expense of several existing ones, whose intensity was significantly reduced. The most pronounced spectral changes were assigned to corresponding vibrational modes using quantum chemical calculations. A clear-cut correlation was found between temperature-dependent effective magnetic moment of studied compounds and the observed VT-FTIR spectra. Importantly, VT-FTIR confirmed coexistence of two types of copper(II)-nitroxide clusters during gradual magnetostructural transition. Such clusters correspond to weakly coupled and strongly coupled spin states, whose relative contribution depends on temperature. The pronounced difference in the VT-FTIR spectra of two states in breathing crystals is a fingerprint of magnetostructural transition, and understanding of these characteristics achieved by us will be useful for future studies of breathing crystals as well as their diamagnetic analogues.

Influence of intense THz radiation on spin state of photoswitchable compound Cu(hfac)2L(Pr).

The family of magnetoactive compounds Cu(hfac)(2)L(R) exhibits thermo- and photoswitching phenomena promising for various applications. Photoswitching of the Cu(hfac)(2)L(Pr) compound can be observed at temperatures below 20 K and is accompanied by transition to metastable structural state. Reverse conversion to stable structure could not be induced by light of near-IR-vis-UV regions up to date. The far-IR spectra of metastable and stable structural states are different and show characteristic absorption lines in the range of 170-240 cm(-1). These frequencies are accessible by NovoFEL - high-power THz free-electron laser user facility in Novosibirsk. We investigate selective influence of THz radiation on relaxation processes from metastable to stable structural state, which can be monitored by electron paramagnetic resonance (EPR). For this purpose, the experimental station based on X-band EPR spectrometer has been constructed by the THz beamline of NovoFEL and equipped with multimodal THz waveguide allowing to fed radiation directly into the EPR resonator. It has been found that irradiation of studied compound with high-power THz light causes significant but nondestructive increase of its temperature. Apart from this effect, no resonant influence of THz irradiation on relaxation processes has been observed. The experimental results have been rationalized taking into account vibrational relaxation times of the studied compound. Further experiments based on pulse heating by THz radiation have been proposed.

Near-infrared luminescence of RbPb2Cl5:Bi crystals.

A wideband near-IR (NIR) luminescence centered at 1080 nm was found in a RbPb(2)Cl(5):Bi single crystal grown by the Bridgman technique. Absorption, luminescence, and excitation of luminescence spectra were investigated at room and cryogenic temperatures. The luminescence was proposed to be due to the (3)P(1)-->(3)P(0) transition in Bi(+) ion.