Spectra Of Crystals Research Articles

Structure, heat capacity and Raman spectra of Ba2MgWO6 single crystals grown in BaCl2-MgCl2 flux

We present a new method of Ba2MgWO6 single crystal synthesis that allows to grow larger crystals using a BaCl2 and MgCl2 flux. Difficulties to grow single crystals of a size suitable for macroscopic material property measurements caused the majority of characterisation being published on polycrystalline samples. Our single crystal diffraction and energy dispersive X-ray analysis confirmed high quality of synthesised samples. Heat capacity measurements from 300 K to 2 K do not show any phase transitions. However, Raman spectra measured down to 77 K contain additional weak peaks at all temperatures probed, which is in a contrast with only 4 Raman active modes expected from the crystal structure with the space group Fm3¯m. This calls for a more detailed study of potential symmetry breaking that could also influence the electronic properties of the material.

A Guide to Tris(4-Substituted)-triphenylmethyl Radicals.

Triphenylmethyl (trityl, Ph3C•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)3C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials. We report here robust syntheses of six electronically varied (4-RPh)3C•, where R = NMe2, OCH3, tBu, Ph, Cl, and CF3. The characterization reported for the radicals and related compounds includes five X-ray crystal structures, electrochemical potentials, and optical spectra. Each radical is best accessed using a stepwise approach from the trityl halide, (RPh)3CCl or (RPh)3CBr, by controllably removing the halide with subsequent 1e- reduction of the trityl cation, (RPh)3C+. These syntheses afford consistently crystalline trityl radicals of high purity for further studies.

Design of blood plasma concentrations sensor based on a one-dimensional photonic crystal

Abstract This study uses the transfer matrix method to calculate the transmittance spectrum of a one-dimensional photonic crystal (1D-PC). Herein, the crystal is composed of alternating layers of barium titanate ferroelectric and yttrium oxide dielectric. The spatial periodicity of the 1D-PC is broken by a cavity surrounded by thin layers of a critical high-temperature superconductor, which can be used to detect refractive index changes of plasma cells infiltrated into the cavity. The results reflect the existence of a maximum transmittance peak in the telecom region known as a localized mode within the photonic band gap. This study reveals that the localized mode shifts toward longer wavelengths as the operating temperature of the superconductor increases. Additionally, we calculate the sensitivity and quality factor of the localized mode, thereby finding that these quantities increase as the incidence angle increases. The proposed model works in cryogenic temperature environments and may be integrated into biosensor designs.

OPTICAL PROPERTIES OF HgGaInS4 CRYSTALS

Luminescence, transmission, reflection, and wavelength modulation transmission and wavelength modulation reflection spectra of HgGaInS4 crystals were researched in the temperature range of 300-10 K. This article discusses the various features observed in the spectra of HgGaInS4 crystals. The dependence on temperature of the energy gap is shown. Spectra of wavelength modulation transmission have minima a1, a2, and a3, which vary with temperature and are caused by indirect transitions L-Г with phonon absorption and emission. Spectra of thicker crystals have more features caused by the same indirect transitions. The photoluminescence show a strong maximum at 2.43 eV, attributed to radiative recombination of free excitons. These various features have significant implications for the understanding of the electronic and optical properties of HgGaInS4 crystals.

High-Resolution Spectroscopy of the ErCrO3 Crystal: A New Phase Transition?

Infrared absorption spectra of the ErCrO3 crystal in the region of f{-} f transitions in the Er3+ ion are recorded for the first time. An analysis of high-resolution temperature-dependent spectra reveals a step at T{kern 1pt} ' = 47 K on the temperature dependences of the characteristics of spectral lines, in addition to the features at temperatures of magnetic ordering TN = 133 K and spin-reorientation transition {{T}_{{{text{SR}}}}} = 9.3{kern 1pt} K. This feature can be associated with either a previously unknown phase transition or with local changes in the crystal structure. The shape of the lines at liquid helium temperatures indicates the presence of additional positions for Er3+ ions in the ErCrO3 crystal. Presumably, these are positions near uncontrolled impurities that enter the crystal during its growth by the solution–melt method and form regions with a distorted structure responsible for the occurrence of polarization.

A comprehensive study on intrinsic alpha corpuscular radiation damage in monazite crystals using picometer-scale imaging, coupled with SCXRD and Raman spectroscopy

We have investigated monazite crystals, known to experience lattice distortions due to alpha particle emission from their atomic nuclei. Our aim in this investigation is to study the complex relationship between the lattice parameters and Raman spectra of monazite crystals. Through this study, we seek to understand the interdependency between these physical parameters and their influence on one another for an improved understanding of radiation-induced damage in these crystals. In addition to this, we also attempted to establish a correlation between these properties and their picometer-scale images to gain a deeper understanding of the structural changes that occur at the atomic scale. We conducted our study on four monazite samples withstanding intrinsic alpha decay radiation, denoted as M1, M2, M3, and M4, with crystal unit cell volume ranging from 299.961 Å3 to 301.96 Å3. Our Pearson statistical analysis revealed a correlation R2 (0.96) between the SCXRD-derived Ce–P Distance of monazite and the FWHM of PO4 band active mode in Raman spectra. This indicated lattice distortions due to alpha decay radiation impacting the Raman spectra. While Raman PO4 band broadening can be a consequence of impurities, dopants, and radiation damage, HRTEM scrutiny of the samples at picometer scales revealed the presence of point defects, plane rotation, and lattice distortions within the samples, suggesting the impact of alpha decay on the crystal lattice. HRTEM analysis has added additional confirmation that the major contribution to PO4 band broadening is due to alpha radiation damage in these samples. Through our study, we conclude a multiple-approach correlation is necessary to accurately study radiation damage dynamics at atomic scales.

Thickness Dependence on Wavelength Range of Random Laser in Ultrathin ZnO Crystals Grown by Mist-CVD on C-plane Sapphire Substrate

The ultrathin ZnO crystals were grown by mist chemical vapor deposition technique with potentially low-cost and low-environmental impact on commercially available c-plane sapphire substrates. The photoluminescence spectra of the ultrathin ZnO crystals were evaluated, and we observed the random lasing behaviors. In addition, the range of random laser wavelengths of photoluminescence can be shifted with a constant trend by changing the structural parameters of the ultrathin ZnO crystals. Here, the structural parameter was the thickness of the ultrathin ZnO crystals. The results indicate that the oscillation wavelength range of the random laser may be potentially fine-tuned by changing the structural parameters of the random laser medium.

Growth and spectroscopic properties of a novel Tm3+-doped YSr3(PO4)3 disordered crystal

A novel Tm3+-doped YSr3(PO4)3 (Tm:YSP) crystal with a disordered crystal structure was grown by using the Czochralski pulling method. The single crystal growth, structure, absorption and emission spectra were systematically analyzed. The absorption bandwidth at ∼792 nm was found to be 21 nm, showing that the Tm:YSP crystal was very suitable for commercial laser diodes pumping of AlGaAs. Furthermore, the maximum emission cross section centering at 1835 nm was determined to be 0.86 × 10−20 cm2 with an emission bandwidth of 202 nm, which indicates the promising applications in the fields of ultrafast and tunable lasers. In addition, Spectroscopic parameters, containing Judd – Ofelt intensity, line strengths, radiative transition probabilities, fluorescence branching ratio and radiative lifetime, were analyzed by using the Judd – Ofelt theory. All above results showed that the Tm:YSP crystal with a disordered structure was a potential laser medium in the ⁓ 2 μm region.

Lattice-dynamics study of Raman-active modes in LaTiO3

The lattice dynamics plays an important role in the determining the orbital and magnetic ordering phenomena in rare-earth (R) RTiO3 titanates. In the present study, the assignment and vibrational character of Ag and B2g-symmetry phonons observed in the Raman spectra of LaTiO3 crystal is verified by shell-model calculations of eigenfrequencies, relative intensities, and eigenvector components of the normal modes. The eigenvector pattern of the Ag mode located around the most pronounced central mode at 296cm−1 is turned out to be in full agreement with the La–O covalency in LaTiO3, where the concomitant GdFeO3-type distortion is decisive. The GdFeO3-type mode is located in the close proximity to the Jahn-Teller (JT) tetragonal E-type Qε mode. An interplay between the R–O covalency and JT effects can determine the subtle conditions for the electronic ground state of the Ti3+ ion and associated orbital and magnetic ordering phenomena in RTiO3 titanates.

Synthesis, crystal growth, electronic structures and optical properties of wide bandgap semiconductor (CH3NH3)2HgI4

The synthesis, crystal growth and electronic structures, as well as optical properties of Hg-based hybrid organic-inorganic compound (CH3NH3)2HgI4 are reported. Single crystal was grown through the anti-solvent method, yielding the faint yellow (CH3NH3)2HgI4 flake crystals. The structural analysis revealed that (CH3NH3)2HgI4 crystallized in the orthorhombic space group Pbca with a 0D crystal structure featuring anionic [HgI4]2- units that were surrounded by CH3NH3+ cations. Furthermore, (CH3NH3)2HgI4 does not decompose when being exposed to air, but the crystallinity slowly decays over time in air at room temperature. TGA and DSC show that it is stable for (CH3NH3)2HgI4 from room temperature to 223 °C. It shows that (CH3NH3)2HgI4 is a slightly indirect nature with 3.276 eV of band gap based on density functional theory calculations, which is close to 3.18 eV derived from UV–vis–NIR spectra of (CH3NH3)2HgI4 crystal. In addition, room temperature photoluminescence (PL) spectra of (CH3NH3)2HgI4 yields broad peaks at 540 nm with full width at half maximum (FWHM) values of 201 nm. These PL peaks are tentatively assigned to self-trapped excitons following the crystal and electronic structure considerations. The bands around the Fermi level have small dispersions, which is indicative of high charge localization with significant exciton binding energies in (CH3NH3)2HgI4. PL analysis indicates that (CH3NH3)2HgI4 may have potential research value as white-light-emitting phosphors and scintillator.

Influence of the Magnetic Domain Structure on Polarization Effects in the Mössbauer Spectra of Iron Borate FeBO3 Single Crystals

The Mössbauer spectra of FeBO3 single crystals are studied at temperatures above and below the magnetic transition point at different orientations of the crystals with respect to the propagation direction of γ rays. To describe the Mössbauer spectra, a theoretical model is developed with allowance for different orientations of magnetic moments in the crystal plane. It is found that the magnetic domain structure in iron borate significantly affects the shape of the Mössbauer spectra and the intensity of resonant transitions. The proposed model may be useful for determining the configuration of the magnetic domain structure of materials from Mössbauer spectroscopy data.

Hypercubane covalent crystals: Insight from density functional theory

A series of new covalent crystals inspired by the carbon tesseract or hypercubane has been introduced using the density functional theory (DFT) calculations. Three types of possible packing of hypercubane crystals were identified: simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc). Based on the structure of the materials, it follows that the hypercubane crystals cannot be attributed to superdense materials, since their density is inferior to that of the diamond. An analysis of the electronic characteristics showed that crystals with sc and bcc packing belong to the class of semiconductors, whose band gaps are 2.23 and 1.46 eV, respectively, while a crystal with fcc packing possesses a metallic nature. The calculated Raman and IR spectra for semiconductor hypercubane crystals made it possible to find characteristic peaks for their identification. Thus, the characteristic IR peaks for sc hypercubane turned out to be at frequencies of 1053 and 1205 cm–1, and for the bcc hypercubane, the characteristic peak turned out to be only one at the frequency of 851 cm–1. For the Raman spectrum, the characteristic frequency values were 961 and 1300 cm−1 for sc hypercubane crystal and 1051, 1142, and 1764 cm–1 for bcc covalent hypercubane. The calculated UV–visible spectra for both the sc and bcc crystals showed an absorption maximum of ∼100 nm, which corresponds to the far UV region.

Modification of calcium orthovanadate single crystal due to cobalt doping

Activation of calcium orthovanadate crystals by cobalt ions was carried out by introducing cobalt oxide into the melt during Czochralski growth process or during high-temperature annealing of nominally pure Ca3(VO4)2 single-crystal using Co3O4 powder as a solid-phase diffusant. The maximum concentration of the Co ions in the matrix is achieved in the case of the diffusion doping process. For the concentration series of Ca3(VO4)2:nCo crystals, the local structure was investigated and the crystal chemical composition was determined. Polarized absorption spectra of doped crystals are obtained. The influence of the atmosphere and the annealing temperature on the redistribution of the intensities of the characteristic absorption bands in the visible and near-IR spectral regions is shown. Luminescence parameters of the doped crystals were studied.

Discovery of aggregation-induced emission luminogens (AIEgens) from orange peel

In recent years, aggregation-induced emission luminogens (AIEgens) have been widely developed for bio-imaging, theranostics, organic photoelectronics, and chemo/biosensors. While, the existing AIEgens are almost all obtained by organic synthesis, experiencing complicated synthesis routes, high cost, environmentally unfriendly, and poor biocompatibility. Therefore, exploration of AIEgens from natural products is an attractive alternative approach. In this contribution, two natural AIE-active materials, Tangeretin and Nobiletin, were found, which can be extracted from orange peel. Single crystal structure, fluorescence spectra and viscosity analyses verified that restriction of intramolecular rotation was responsible for the AIE phenomenon of Tangeretin and Nobiletin. The theoretical calculation results indicated that the intermolecular charge transfer (ICT) was related with the bathochromic-shift in the solid-state. Moreover, Tangeretin and Nobiletin were biocompatible and could selectively target lysosomes. In short, these natural products provided a new approach for obtaining new kinds of AIEgens, and showing great potential in bioimaging.

A New Look at the Explanation of Differences in Properties between La3+ and Lu3+ Titanate Hosts Occupied by Eu3+

In order to improve the quality of WLEDs, considerable efforts have been devoted to investigate red phosphor. In this study, two double perovskites La2MgTiO6 and La2ZnTiO6 and two novel pyrochlores Lu2MgTiO6 and Lu2ZnTiO6 doped with 1%Eu3+ were synthesized by the co-precipitation method. The crystal structure, absorption, excitation, and emission spectra of all samples were investigated in detail. Dissimilar luminescent behaviors of the studied samples were observed. Due to the different site symmetry of Eu3+, each compound exhibits a different emission spectrum. The emission of the magnetic dipole transition is dominant in all the spectra of the Lu-based hosts, while the forced electric dipole transition is the strongest one in the spectra of the others. Besides, the ones crystallized in double perovskite structures possess larger bandgaps and show a more intense emission from the 5D1 level of Eu3+ as compared to the pyrochlore compounds. Furthermore, the distinct mechanism of the cross-relaxation of four titanate compounds was investigated. The above findings contribute to the understanding of the two novel pyrochlore hosts.

Radiation and Emission Phenomena in Combination

Radiation and Emission Phenomena in Combination

Topological phonon analysis of the two-dimensional buckled honeycomb lattice: An application to real materials

By means of group theory, topological quantum chemistry, first-principles, and Monte Carlo calculations, we analyze the topology of the 2D buckled honeycomb lattice phonon spectra. Taking the pure crystal structure as an input, we show that eleven distinct phases are possible, five of which necessarily have nontrivial topology according to topological quantum chemistry. Another four of them are also identified as topological using Wilson loops in an analytical model that includes all the symmetry allowed force constants up to third-nearest neighbors, making a total of nine topological phases. We then compute the ab initio phonon spectra for the two-dimensional crystals of Si, Ge, P, As, and Sb in this structure and construct its phase diagram. Despite the large proportion of topological phases found in the analytical model, all of the crystals lie in a trivial phase. By analyzing the force constants space using Monte Carlo calculations, we elucidate why topological phonon phases are physically difficult to realize in real materials with this crystal structure.

PCMW2D and 2D Raman correlation spectroscopy evidence for presence of spin-phonon coupling in hexagonal LuMnO3

Two-dimensional correlation spectroscopy (2D-COS) and perturbation-correlation moving window two-dimensional correlation spectroscopy (PCMW2D) analysis are performed on the temperature-dependent Raman spectra of hexagonal LuMnO3 single crystal. Under the resonance with the on-site Mn d-d transitions, the correlation between the phonons which are relate to the vibration of Mn ions’ bonds and spin-excitation peaks suggest a strong spin-phonon coupling in LuMnO3. The PCMW2D results clearly show that the significant change in phonons and spin-excitation peaks occurs around the Néel temperature and the spin reorientation transition. The multiple components in the broad spin-excitation peaks also suggest variations in spin symmetries in the ground state. Furthermore, we propose that the 2D-COS and PCMW2D Raman correlation spectroscopies provide a simple and powerful method for investigating the couplings and the transitions, which would be very important for understanding systematically the magnetoelectric properties of multiferroic materials.

Crystal effects in the vibrational spectra of one-dimensional molecular spin crossover crystals using molecular dynamics simulations

We use molecular dynamics simulations to model the iron phonon density of states (pDOS) of a spin crossover (SCO) crystal built from 39-nuclear [Fe(atrz)_3Cl_2] chains (atrz = 4-amino-1,2,4-triazole). This is possible by using an atomistic potential that depends on the spin state of the Fe atoms. While quantum-chemical methods are able to provide data on isolated SCO molecules, the computational costs necessitate the use of classical simulations to calculate crystal effects on the spectra. Data are provided for a high-spin (HS) crystal, in which all Fe atoms are in their HS state, and a low-spin (LS) crystal. HS and LS crystals show distinctively different spectra that are in agreement with experimental data. Compared to the single-molecule spectra, the crystal spectra show several distinctive features: (i) The spectra are smoother, and the main peaks are slightly reduced in amplitude. (ii) The effect of intermolecular interactions shows up in additional structure at long-wavelengths. Good agreement between experimental and simulated phonon spectra is observed. The lattice-dynamics analysis of the low-energy pDOS allows to extract the temperature dependence of the vibrational entropy of the LS and HS crystals. Our study thus provides novel information about the crystal effects in SCO crystals.

Structural and functional characterization of the catalytic domain of a cell-wall anchored bacterial lytic polysaccharide monooxygenase from Streptomyces coelicolor

Bacterial lytic polysaccharide monooxygenases (LPMOs) are known to oxidize the most abundant and recalcitrant polymers in Nature, namely cellulose and chitin. The genome of the model actinomycete Streptomyces coelicolor A3(2) encodes seven putative LPMOs, of which, upon phylogenetic analysis, four group with typical chitin-oxidizing LPMOs, two with typical cellulose-active LPMOs, and one which stands out by being part of a subclade of non-characterized enzymes. The latter enzyme, called ScLPMO10D, and most of the enzymes found in this subclade are unique, not only because of variation in the catalytic domain, but also as their C-terminus contains a cell wall sorting signal (CWSS), which flags the LPMO for covalent anchoring to the cell wall. Here, we have produced a truncated version of ScLPMO10D without the CWSS and determined its crystal structure, EPR spectrum, and various functional properties. While showing several structural and functional features typical for bacterial cellulose active LPMOs, ScLPMO10D is only active on chitin. Comparison with two known chitin-oxidizing LPMOs of different taxa revealed interesting functional differences related to copper reactivity. This study contributes to our understanding of the biological roles of LPMOs and provides a foundation for structural and functional comparison of phylogenetically distant LPMOs with similar substrate specificities.