Single-crystal Spectra Research Articles

Electron Paramagnetic Resonance Study of the Radiation Damage Centers in Menadione Single Crystal

The radiation damage centers in the 60Co- rays irradiated menadione (2-methyl-1,4-naphthoquinone; Vitamin K3; C11H8O2 ) single crystals were examined at 120 K by Electron Paramagnetic Resonance (EPR) spectroscopy. The presence of two radicals was detected in the compound. Both radicals are carbon centered radicals. Analysis of the EPR spectra of gamma-irradiated menadione single crystals along three different axes showed that the C(11)-H(19) bond of the compound was broken. It was determined that the unpaired electron located on the C(11) atom. The g values and the hyperfine structure constants of the radiation damage centers observed in menadione single crystal were obtained. Accuracy of experimental data was observed by simulation study.

Defect energy levels in monoclinic β-Ga2O3

The defect levels in semiconductor are crucial to the performance of related devices. However, the positions of the defect levels in monoclinic β-Ga2O3, such as that for oxygen vacancy (VO), Ga–O divacancy, and self-trapped hole (STH), are still controversial. In this paper, we systematically investigated the photoluminescence and photoluminescence excitation spectra of undoped, Si-doped, and Mg-doped β-Ga2O3 single crystals grown by the edge-defined film-fed growth method. It is found that the oxygen vacancies are deep donors and their levels are related to the coordinations of the vacancies. For each crystal, the recombination between VO and Ga–O divacancy levels is the origin of the blue emission, and the red emission originates from the transition from VO to STH levels. The location of STH level is also related to the geometrical position of oxygen. For the Si-doped crystal, no red emission is observed due to the annihilation of STHs. While a Mg impurity level is produced at ∼1 eV above the valence band maximum, which causes an extra red emission in the spectra of Mg-doped crystal. Our results strongly support the recent theoretical results obtained via first-principle calculations [Q. D. Ho et al., Phys. Rev. B 97 (2018) 115163] and could be benefit for designing β-Ga2O3 related devices.

Experimental and Computational Interaction Studies of (E)-N’-Benzylidene-5-Methyl-1H-Pyrazole-3-Carbohydrazide with α-Glucosidase and α-Amylase Enzymes: A Detailed Structural, Spectroscopic, and Biophysical Study

Herein we report the synthesis, DFT calculations, and molecular docking studies of a pyrazole derivative, (E)-N'-benzylidene-5-methyl-1H-pyrazole-3-carbohydrazide (E-BMPC) as α-glucosidase and α-amylase inhibitor. Molecular structure of E-BMPC has been confirmed by single crystal X-ray diffraction (XRD), FTIR, 1H, and 13C NMR spectra. In addition, density functional theory (DFT) calculations on E-BMPC were carried out to obtain frontier molecular orbital energies and first-order static hyperpolarizability (β). The α-amylase and α-glucosidase enzyme inhibitory of E-BMPC was also tested. E-BMPC displayed moderate inhibitory activity with IC50 values 310.57 ± 2.67 and 182.19 ± 3.20 against α-glucosidase and α-amylase enzymes, respectively. Molecular docking analysis provided the inhibition constant of E-BMPC molecule for α-amylase enzyme as 33.60 µM. Both in vitro and in silico enzyme inhibition studies showed that E-BMPC molecule is a better inhibitor for α-amylase than α-glucosidase. The β parameter for the molecule under investigation was also calculated as 4.2 × 10−30 esu.

Synthesis, structure and photocatalytic properties of two novel Cd (II) coordination polymers based on 1-[(2-methyl-1H-benzoimidazol-1-yl) methyl]-1H-benzotriazole

Two new coordination polymers (CPs) [Cd(mbmb)I2]n (1) and {[Cd2(mbmb)3I2 (SCN)2]·0.25(H2O)}n (2) have been synthesized with 1-[(2-methyl-1H-benzoimidazol-1-yl)methyl]-1H-benzotriazole (mbmb), and structurally characterized by X-ray single crystal diffraction analysis, elemental analysis, 1HNMR spectra and IR spectra. The X-ray analysis reveals that both polymers 1–2 crystallize in the triclinic space group P-1. Polymer 1 displays 1D chain structure and further connected through two different intermolecular π…π stacking interactions to form a 2D network. Polymer 2 possesses a 2D layer network, which is further extended into more stable 3D architecture. Moreover, polymers 1–2 were examined for photocatalytic degradation activities, and the result shows that they both present outstanding photocatalytic activities for the degradation of MB and RhB with remarkable efficiencies. For MB, the degradation efficiencies are 96.12% (1) and 95.59% (2); for RhB, the degradation efficiencies are 97.14% (1) and 94.51% (2). Polymer 1 shows higher photocatalytic performance in the degradation of MB and RhB.

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The paper presents the transmission spectra of hybrid perovskite MAPbI3 single crystals near the fundamental absorption edge in a wide temperature range. The absorption coefficient α of the single crystal samples is estimated at a temperature T = 150 K for the light with a photon energy E = 1.6 eV and at T = 40 K for E = 1.8 eV. The obtained values turned out to be several orders of magnitude smaller than the values of α for thin-film samples known from the literature. A sharp shift of the fundamental absorption edge by ~ 100 meV was observed at a temperature T1 = 160 K of the structural phase transition from the tetragonal to the orthorhombic phase. The temperature hysteresis of the shift of the fundamental absorption edge near T1 was recorded, which is characteristic of a first-order phase transition.

Спектры пропускания монокристаллов гибридных перовскитов MAPbI-=SUB=-3-=/SUB=- вблизи края фундаментального поглощения

The paper presents the transmission spectra of hybrid perovskite MAPbI3 single crystals near the fundamental absorption edge in a wide temperature range. The absorption coefficient α of the single crystal samples is estimated at a temperature T = 150 K for the light with a photon energy E = 1.6 eV and at T = 40 K for E = 1.8 eV. The obtained values turned out to be several orders of magnitude smaller than the values of α for thin-film samples known from the literature. A sharp shift of the fundamental absorption edge by ~ 100 meV was observed at a temperature T1 = 160 K of the structural phase transition from the tetragonal to the orthorhombic phase. The temperature hysteresis of the shift of the fundamental absorption edge near T1 was recorded, which is characteristic of a first-order phase transition.

Paramagnetic centers in chromium-doped scandium orthosilicate

The EPR spectrum of single crystals of scandium orthosilicate doped with chromium was studied in the X-band. In the crystallographic and local coordinate systems, the parameters of the spin Hamiltonians of two Cr3+ centers that have replaced scandium in the nonequivalent triclinic positions and demonstrate orthorhombic symmetry in the principal axes are determined. The spectrum of the Gd3+ center localized in one of scandium position was discovered and studied, and the parameters of the fine structure of its ground state were determined. In the studied crystals, EPR signals of unidentified paramagnetic centers also were observed. Keywords: scandium orthosilicate, impurity ions, paramagnetic resonance.

Парамагнитные центры в легированном хромом ортосиликате скандия

The EPR spectrum of single crystals of scandium orthosilicate doped with chromium was studied in the X-band. In the crystallographic and local coordinate systems, the parameters of the spin Hamiltonians of two Cr3+ centers that have replaced scandium in the nonequivalent triclinic positions demonstrate orthorhombic symmetry in the principal axes are determined. The spectrum of the Gd3+ center localized in one of scandium position was discovered and studied, and the parameters of the fine structure of its ground state were determined. In the studied crystals, EPR signals of unidentified paramagnetic centers also were observed.

Nanosecond and Highly Sensitive Scintillator Based on All-Inorganic Perovskite Single Crystals.

The scintillator is a unique class of luminescent materials, which is of great significance in clinical diagnosis, security inspection, and radiation detection. Herein, an all-inorganic Cs4PbI6 single crystals (SCs) as a nanosecond and an efficient X-ray and α particle scintillator is described. The radioluminescence (RL) spectrum of Cs4PbI6 SCs under X-ray excitation consists of a band gap emission at 310 nm and a broadband emission at 552 nm at room temperature. Furthermore, Cs4PbI6 SCs demonstrate nanosecond decay times of 0.95 and 6.86 ns, a high sensitivity to low-energy X-ray (30 keV) with a low detection limit (187 nGyair/s), and a favorable linearity detection range, potentially enabling their broad application in X-ray imaging. Under 237Np α particle irradiation, the light yield of Cs4PbI6 SCs is about 49.5% of that of a BGO scintillator with an energy resolution of 35% at 4.78 MeV. Our results demonstrate the potential of Cs4PbI6 SCs as a nanosecond and low-cost scintillator in radiation detection applications.

Modeling dark- and light-induced crystal structures and single-crystal optical absorption spectra of ruthenium-based complexes that undergo SO2-linkage photoisomerization.

A family of coordination complexes of the type [Ru(SO2)(NH3)4X]m+Yn - (m, n = 1 or 2) exhibit optical switching capabilities in their single-crystal states. This striking effect is caused by the light-induced formation of SO2-linkage photoisomers, which are metastable if kept at suitably cool temperatures. We modeled the dark- and light-induced states of these large crystalline complexes via plane-wave (PW)- and molecular-orbital (MO)-based density functional theory (DFT) and time-dependent DFT in order to calculate their structural and optical properties; the calculated results are compared with experimental data. We show that the PW-DFT-based periodic models replicate the structural properties of these complexes more effectively than the MO-DFT-based molecular-fragment models, observing only small deviations in key bond lengths relative to the experimentally derived crystal structures. The periodic models were also found to more effectively simulate trends seen in experimental optical absorption spectra, with optical absorbance and coverage of the visible region increasing with the formation of the photoinduced geometries. The contribution of the metastable photoisomeric species more heavily focuses on the lower-energy end of the spectra. Spectra generated from the molecular-fragment models are limited by the geometry of the fragment used and the number of excited-state roots considered in those calculations. In general, periodic models outperform the molecular-fragment models owing to their ability to better appreciate the periodic phenomena that are present in these crystalline materials as opposed to MO approaches, which are finite methods. We thus demonstrate that PW-DFT-based periodic models should be considered as a more than viable method for simulating the optical and electronic properties of these single-crystal optical switches.

Photochromism influence on the luminescence spectrum of Bi4Ge3O12 single crystals doped with Mn

Bi4Ge3O12 crystals doped with Mn exhibit a considerable thermally stable photochromic effect. An additional absorption of light appears in the visible region of the optical absorption spectrum of the crystals irradiated with UV light. In the photoluminescence spectrum, both the intrinsic emission of a pure Bi4Ge3O12 crystal and the emission in the region of 580 nm caused by the presence of Mn2+ ions are observed. After UV exposure, the luminescence intensity of Mn-doped Bi4Ge3O12 crystals decreases. The emission associated with by Mn2+ ions disappears. The luminescence intensity of pure Bi4Ge3O12 decreases due to strong photoinduced absorption of light in this spectral region.

M\xf6ssbauer measurements of GaFeO3 single crystal multiferroic

Mössbauer measurements on single crystal absorbers at room and at low temperatures were performed. The results are fully consistent with previously published reports by other groups. Spectra of single crystals were simultaneously analyzed including magnetic dipole and electric quadrupole interactions. The analysis shows that there is a small component of magnetic moments perpendicular to the magnetic easy axis. Mössbauer data seem not agree with commonly accepted ferrimagnetic structure of GaFeO3.

Synthesis, isomerization, and DFT studies of five-membered heterocyclic ketoximes

A homologous series of five-membered heterocyclic ketoximes is synthesized by condensation reactions of 2-acetylpyrrole, 2-acetylthiophene, and 2-acetylfuran with hydroxylamine hydrochloride. These compounds were fully characterized by X-ray single-crystal diffraction, elemental analysis, 1H NMR, IR, UV-Vis, and fluorescence spectra. Interesting isomerization phenomena are observed for these heterocyclic ketoximes by different characterization methods. By means of 1H NMR and X-ray single-crystal diffraction, it was found that 2-acetylpyrrole oxime (1) exists as the Z-type geometric isomer, 2-acetylfuran oxime (3) exists as the E-isomer, while 2-acetylthiophene oxime (2) is identified as a mixture of Z- and E-isomers. To study the above phenomena further, quantum chemical calculations of total energy, dipole moment, EHOMO, ELUMO, and other parameters of each heterocyclic ketoxime were carried out by Density functional theory (DFT). The theoretical calculations were in good accordance with the experimental spectroscopic results.

A unitary fluorescence probe to sense Co2+: Validated by theoretical studies and X-ray crystallography

A new salamo-type fluorescence probe H2L was synthesized by a series of reactions and corroborated by single-crystal X-ray crystallography and 1H NMR spectra. Fluorescence of Co2+ selectively response showed “off” when cations were sequentially detected. The LOD of H2L to Co2+ was calculated to be 3.73 × 10-7 M in DMF/water (9:1, v/v) solution system. Meanwhile, the single crystal of the Co2+ complex with H2L was obtained by solvent evaporation. The structure of the complex [Co3(L)2(MeOH)2(μ-OAc)2]·2MeOH was validated by single-crystal X-ray diffraction, IR, and elemental analyses, and the mechanism of recognition of Co2+ by H2L was got. Density functional theory (DFT) and Hirshfeld surface analyses were investigated to further understand the experimental results observed.

A self-sensitized Co (II)-MOF for efficient visible-light-driven hydrogen evolution without additional cocatalysts

Herein, a new metal-organic framework (MOF) {[Co(azpy) (bps) (H2O)]·DMF·2.3H2O}n, 1, (azpy ​= ​4,4′-azopyridine, H2bps ​= ​4, 4′- bibenzoic acid-2, 2′-sulfone (H2bps) has been synthesized by solvothermal method. Complex 1 was characterized in detail by X-ray single-crystal diffraction, elemental analysis, IR spectrum, PXRD and thermogravimetric analysis. X-ray single-crystal diffraction analysis for 1 indicates that two azpy ligands bearing unusual cis-configuration bridge two Co2+ cations, forming an interesting one-dimensional nanopore channel. And these nanopore channels finally form a three-dimensional framework by multiple π···π stacking interactions. Besides, visible-light-driven H2 production exhibited that complex 1 displayed a high-efficiently photocatalytic hydrogen generation (1.44 ​mmol ​g−1·h−1) without additional photosensitizers and cocatalysts. Moreover, the photocurrent response of 1, solid-state UV–Vis absorption spectra of 1 and free ligands were also explored.

Four new CuI/AgI-based coordination compounds containing 2-mercapto-5-methyl-1,3,4-thiadiazole: Synthesis, crystal structures and fluorescence properties

Effectively constructing CuI/AgI-based coordination polymers containing Hmthd ligands is a challenging work, here, four new coordination compounds [Cu(Hmthd)2Cl]n (1), [Cu3(mthd)2Br]n (2), [Ag(mthd)]n (3) and [Ag2(mthd)I]n (4) have been obtained by reactions of the corresponding metal salts and 2-mercapto-5-methyl-1,3,4-thiadiazole (Hmthd) ligand under solvothermal conditions. All the compounds were fully characterized by single-crystal X-ray diffraction, elemental analysis, IR spectrum, thermalgravimetric analysis and powder X-ray diffraction. Compound 1 is a mononuclear coordination compound, in which two neutral Hmthd molecules and CuCl unit are coplanar. In compound 2, the anionic [CuBr(mthd)]22– units and one-dimensional coplanar cationic {[Cu2(mthd)]+}n chains are connected to each other to form a two-dimensional layered structure. In compound 3, two different one-dimensional puckered [Ag(mthd)]n chains are connected to each other to form a two-dimensional irregular layered structure, in which a (AgS)n chain constructed by staggered Ag3S3 rings is observed. Compound 4 is a two-dimensional double layer coordination framework containing a two-dimensional inorganic (Ag2IS)n double layer. Compound 4 shows the apparent yellow emission with the maximum at 551 nm while exciting at 333 nm, and displays sensitive luminescence quenching response to nitrobenzene with quenching constant (Ksv) of 5.07 × 103 M−1 and detection limit of 5.33 × 10−6 M. This research provides a new strategy to construct the CuI/AgI-based coordination compounds containing Hmthd ligands with extended structures through the synergistic effect of (mthd)- and halide ions.

Anion-Dependent Electron Transfer in the Cyanide-Bridged [Fe2Co2] Capsules.

A family of molecular capsules, {[(Tp*)Fe(CN)3Co(bpyC═N(CH2)7N═Cbpy)]2[X]2}·sol (1, X = ClO4, sol = 6DMF; 2, X = PF6, sol = 6DMF; 3, X = OTf, sol = 6DMF; 4, X = BPh4, sol = 2DMF; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; bpy = 2,2'-bipyridine), were prepared via the Schiff-base condensation of the aldehyde-substituted bpy (bpyCHO) and 1,7-diaminoheptane (H2N(CH2)7NH2). All the complexes contain the same cyanide-bridged cationic square cores ([Fe2Co2]2+), which are encapsuled by the flexible alkyl chains. Variable-temperature single-crystal X-ray diffraction, FT-IR spectra, and magnetic studies reveal the abrupt and complete, thermo- and photo-induced electron-transfer-coupled spin transition for 1-3, while the pure high-spin phase for 4. Such distinct behavior is attributed to the effective long-range cooperative interactions mediated by the intercluster π-π couplings in 1-3, which, however, are significantly blocked in 4 due to the steric effect of interstitial BPh4- anions. Furthermore, the shift in the thermally induced transition temperatures of 254 K for 1, 233 K for 2, and 187 K for 3, respectively, is likely correlated to the variable H···O and H···F interactions between the solvent molecules, anions, and the bipyridine ligands of the [Fe2Co2] squares, suggesting the significant anion-dependent effect in such a system.

Exciton dispersion in para-quaterphenyl: Significant molecular interactions beyond Coulomb coupling

We have experimentally determined the momentum dependence of the electronic excitation spectra of para-quaterphenyl single crystals. The parallel arrangement of para-quaterphenyl molecules results in a strong Coulomb coupling of the molecular excitons. Such crystals have been considered to be a very good realization of the Frenkel exciton model, including the formation of H-type aggregates. Our data reveal an unexpected exciton dispersion of the upper Davydov component, which cannot be rationalized in terms of inter-molecular Coulomb coupling of the excitons. A significant reduction of the nearest neighbor coupling due to additional charge-transfer processes is able to provide an explanation of the data. Furthermore, the spectral onset of the excitation spectrum, which represents a heavy exciton resulting from exciton–phonon coupling, also shows a clear dispersion, which had been unknown so far. Finally, an optically forbidden excitation about 1 eV above the excitation onset is observed.

Non-π-Conjugated Deep-Ultraviolet Nonlinear Optical Crystal K2Zn3(SO4)(HSO4)2F4.

Deep-ultraviolet (deep-UV) (wavelengths of <200 nm) nonlinear optical (NLO) materials are playing an increasingly important role because of their significant technological applications in advanced scientific instruments. In recent years, the non-π-conjugated systems have received extensive attention as new emerging sources of deep-UV NLO materials. Here, a new non-π-conjugated deep-UV NLO material, K2Zn3(SO4)(HSO4)2F4, has been successfully obtained by the hydrothermal method. It has a layered structure formed by [Zn3(SO4)(HSO4)2F3]∞ layers bridged via K-O and K-F bonds. Powder second-harmonic generation shows that K2Zn3(SO4)(HSO4)2F4 can achieve phase matching, and the response is ∼0.3 times that of KH2PO4. Remarkably, the single-crystal transmittance spectrum confirms that the absorption edge of K2Zn3(SO4)(HSO4)2F4 is below 200 nm, and the experimentally measured birefringence is 0.0126 at λ = 546 nm. In-depth first-principles calculations illustrate well the microscopic origin of the optical properties. This work enriches the structrual diversity of non-π-conjugated deep-UV NLO materials.

Vibrational anisotropy of &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;-(Al,Fe)OOH single crystals as probed by nuclear resonant inelastic X-ray scattering

Abstract. The formation of high-pressure oxyhydroxide phases spanned by the components AlOOH–FeOOH–MgSiO2(OH)2 in experiments suggests their capability to retain hydrogen in Earth's lower mantle. Understanding the vibrational properties of high-pressure phases provides the basis for assessing their thermal properties, which are required to compute phase diagrams and physical properties. Vibrational properties can be highly anisotropic, in particular for materials with crystal structures of low symmetry that contain directed structural groups or components. We used nuclear resonant inelastic X-ray scattering (NRIXS) to probe lattice vibrations that involve motions of 57Fe atoms in δ-(Al0.87Fe0.13)OOH single crystals. From the recorded single-crystal NRIXS spectra, we calculated projections of the partial phonon density of states along different crystallographic directions. To describe the anisotropy of central vibrational properties, we define and derive tensors for the partial phonon density of states, the Lamb–Mössbauer factor, the mean kinetic energy per vibrational mode, and the mean force constant of 57Fe atoms. We further show how the anisotropy of the Lamb–Mössbauer factor can be translated into anisotropic displacement parameters for 57Fe atoms and relate our findings on vibrational anisotropy to the crystal structure of δ-(Al,Fe)OOH. As a potential application of single-crystal NRIXS at high pressures, we discuss the evaluation of anisotropic thermal stresses in the context of elastic geobarometry for mineral inclusions. Our results on single crystals of δ-(Al,Fe)OOH demonstrate the sensitivity of NRIXS to vibrational anisotropy and provide an in-depth description of the vibrational behavior of Fe3+ cations in a crystal structure that may motivate future applications of NRIXS to study anisotropic vibrational properties of minerals.