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Crystals, Volume 9, Issue 12 (December 2019)

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Open AccessArticle
Localized Conical Edge Modes in Optics of Spiral Media (First Diffraction Order)
Crystals 2019, 9(12), 674; https://doi.org/10.3390/cryst9120674 (registering DOI) - 16 Dec 2019
Abstract
In cholesteric liquid crystals (CLC) problems related to the localized optical modes for a non-collinear geometry are studied here in the two wave dynamic diffraction theory approximation. This approximation, which insures the results accuracy order of δ (where δ is the CLC dielectric [...] Read more.
In cholesteric liquid crystals (CLC) problems related to the localized optical modes for a non-collinear geometry are studied here in the two wave dynamic diffraction theory approximation. This approximation, which insures the results accuracy order of δ (where δ is the CLC dielectric anisotropy), is applied because for a non-collinear geometry there is no exact analytic solution of the Maxwell equations and a theoretical description of the experimental data becomes more complicated. The dispersion equation for non-collinear localized edge modes (called conical modes (CEM)) is found and analytically solved for the case of thick layers and for this case the lasing threshold and the conditions of the anomalously strong absorption effect are found. It is shown that qualitatively CEMs are very similar to the localized edge modes (EM) in CLCs related to a collinear geometry, i.e., for the case of light propagation along the spiral axis however the CEMs differ by their polarization properties (the CEM eigen polarizations are elliptical ones depending on the degree of CEM deviation from the collinear geometry in contrast to the circular eigen polarizations in the EM case). What is concerned of the CEM quantitative values of the parameters they are “worth” (the photonic effects are not so pronounced) than for the corresponding ones for EM. The CEM lasing threshold is higher than the one for EM, etc. Performed theoretical studies of possible conversion of EMs into CEMs showed that it can be due to the EM reflection at dielectric boundaries at the conditions of a high pumping wave focusing. Known experimental results on the CEM are discussed and optimal conditions for CEM observations are formulated. Full article
(This article belongs to the Special Issue Localized Optical Modes in Liquid Crystals)
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Open AccessArticle
Subthreshold Characteristics of a Metal-Oxide–Semiconductor Field-Effect Transistor with External PVDF Gate Capacitance
Crystals 2019, 9(12), 673; https://doi.org/10.3390/cryst9120673 - 14 Dec 2019
Viewed by 119
Abstract
An organic ferroelectric capacitor, using polyvinylidene difluoride (PVDF) as the dielectric, was fabricated. By connecting the PVDF capacitor in series to the gate of a commercially purchased metal-oxide–semiconductor field-effect transistor (MOSFET), drain current (ID)–drain voltage (VD) characteristics [...] Read more.
An organic ferroelectric capacitor, using polyvinylidene difluoride (PVDF) as the dielectric, was fabricated. By connecting the PVDF capacitor in series to the gate of a commercially purchased metal-oxide–semiconductor field-effect transistor (MOSFET), drain current (ID)–drain voltage (VD) characteristics and drain current (ID)–gate voltage (VG) characteristics were measured. In addition, the subthreshold slopes of the MOSFET were determined from the IDVG curves. It was found that the subthreshold slope could be effectively reduced by 23% of its original value when the PVDF capacitor was added to the gate of the MOSFET. Full article
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Open AccessReview
Mechanisms of Pressure-Induced Phase Transitions by Real-Time Laue Diffraction
Crystals 2019, 9(12), 672; https://doi.org/10.3390/cryst9120672 - 14 Dec 2019
Viewed by 107
Abstract
Synchrotron X-ray radiation Laue diffraction is a widely used diagnostic technique for characterizing the microstructure of materials. An exciting feature of this technique is that comparable numbers of reflections can be measured several orders of magnitude faster than using monochromatic methods. This makes [...] Read more.
Synchrotron X-ray radiation Laue diffraction is a widely used diagnostic technique for characterizing the microstructure of materials. An exciting feature of this technique is that comparable numbers of reflections can be measured several orders of magnitude faster than using monochromatic methods. This makes polychromatic beam diffraction a powerful tool for time-resolved microstructural studies, critical for understanding pressure-induced phase transition mechanisms, by in situ and in operando measurements. The current status of this technique, including experimental routines and data analysis, is presented along with some case studies. The new experimental setup at the High-Pressure Collaborative Access Team (HPCAT) facility at the Advanced Photon Source, specifically dedicated for in situ and in operando microstructural studies by Laue diffraction under high pressure, is presented. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations)
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Open AccessArticle
Effects of He+ and H+ Co-Implantation with High Energy on Blisters and Craters of Si and SiO2-On-Si Wafers
Crystals 2019, 9(12), 671; https://doi.org/10.3390/cryst9120671 - 12 Dec 2019
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Abstract
In this paper, effects of He+ and H+ co-implantation with high implantation energy on surface blisters and craters at different annealing conditions are systematically investigated. Surface morphology as well as defect microstructure are observed and analyzed by various approaches, such as [...] Read more.
In this paper, effects of He+ and H+ co-implantation with high implantation energy on surface blisters and craters at different annealing conditions are systematically investigated. Surface morphology as well as defect microstructure are observed and analyzed by various approaches, such as scanning electron microscopy (SEM), optical microscopy (OM), atomic force microscopy (AFM), and Raman spectroscopy. It is found that after 500 °C annealing and above for 1 h, surface blisters and exfoliation are observed for Si and SiO2-on-Si wafers except for the samples implanted with only He+ ions. AFM images reveal that the heights of blisters in Si and SiO2-on-Si wafers are 432 nm and 397 nm respectively and the thickness of transfer layer is at the depth of about 1.4 μm, which is consistent with the projected range of He+ and H+ ions. Raman spectroscopy demonstrates that higher annealing temperature can lead to a stronger intensity of the VH2 peak. Under the same implantation parameters, surface morphology of Si and SiO2-on-Si wafers is different after annealing process. This phenomenon is discussed in detail. Full article
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Open AccessEditorial
Liquid Crystal Optics and Physics: Recent Advances and Prospects
Crystals 2019, 9(12), 670; https://doi.org/10.3390/cryst9120670 - 12 Dec 2019
Viewed by 110
Abstract
For more than 100 years, liquid crystals (LCs) have been extensively investigated and LC displays now are becoming ubiquitous in our daily life, from TVs, mobile phones to indoor/outdoor signage [...] Full article
(This article belongs to the Special Issue Liquid Crystal Optics and Physics: Recent Advances and Prospects)
Open AccessArticle
Cohesive Element Model for Fracture Behavior Analysis of Al2O3/Graphene Composite Ceramic Tool Material
Crystals 2019, 9(12), 669; https://doi.org/10.3390/cryst9120669 - 11 Dec 2019
Viewed by 148
Abstract
The microstructure model of Al2O3/graphene (AG) composite ceramic tool material is established based on Voronoi tessellation. The cohesive element method was used to simulate the crack growth of AG. The effect of cohesive parameters at the grain boundary of [...] Read more.
The microstructure model of Al2O3/graphene (AG) composite ceramic tool material is established based on Voronoi tessellation. The cohesive element method was used to simulate the crack growth of AG. The effect of cohesive parameters at the grain boundary of Al2O3 and graphene on the crack propagation was investigated. The results show that the grain strength of graphene is too high, the crack propagation to graphene grains will be hindered and cannot propagate forward. Cracks tend to spread along the paths where the crack propagation drive force was high and the resistance was low. When the interface strength between Al2O3 and graphene was at the weak interface, the crack propagation path and length were relatively straight and short. The average energy release rate is 1.042 × 10−3 J/m2, which is 2.4% higher than that of single-phase Al2O3 ceramic tool materials. However, if the interface strength between Al2O3 and graphene was at the strong interface, the crack propagated along graphene particles for a short distance, consuming a large amount of fracture energy. Furthermore, the crack will deflect around graphene grains, which increases the crack propagation length. The average energy release rate is 1.039 × 10−3 J/m2, which is 2% higher than that of single-phase Al2O3 ceramic tool materials. Full article
Open AccessArticle
Intermolecular Interactions in Ionic Crystals of Nucleobase Chlorides—Combining Topological Analysis of Electron Densities with Energies of Electrostatic Interactions
Crystals 2019, 9(12), 668; https://doi.org/10.3390/cryst9120668 - 11 Dec 2019
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Abstract
Understanding intermolecular interactions in crystals of molecular ions continues to be difficult. On the one hand, the analysis of interactions from the point of view of formal charges of molecules, similarly as it is commonly done for inorganic ionic crystals, should be performed. [...] Read more.
Understanding intermolecular interactions in crystals of molecular ions continues to be difficult. On the one hand, the analysis of interactions from the point of view of formal charges of molecules, similarly as it is commonly done for inorganic ionic crystals, should be performed. On the other hand, when various functional groups are present in the crystal, it becomes natural to look at the interactions from the point of view of hydrogen bonding, π…π stacking and many other kinds of non-covalent atom–atom bonding. Often, these two approaches seem to lead to conflicting conclusions. On the basis of experimental charge densities of cytosinium chloride, adeninium chloride hemihydrate, and guanine dichloride crystals, with the help of theoretical simulations, we have deeply analysed intermolecular interactions among protonated nucleobases, chloride anions and water molecules. Here, in the second paper of the series of the two (Kumar et al., 2018, IUCrJ 5, 449–469), we focus on applying the above two approaches to the large set of dimers identified in analysed crystals. To understand electrostatic interactions, we analysed electrostatic interaction energies (Ees) computed directly from molecular charge densities and contrasted them with energies computed only from net molecular charges, or from a sum of electric multipolar moments, to find the charge penetration contribution to Ees. To characterize non-covalent interactions we performed topological analyses of crystal electron densities and estimated their interaction energies (EEML) from properties of intermolecular bond critical points. We show that the overall crystal architecture of the studied compounds is governed by the tight packing principle and strong electrostatic attractions and repulsions between ions. Many ions are oriented to each other in a way to strengthen attractive electrostatic interactions or weaken strong repulsion, but not all of them. Numerous bond critical points and bond paths were found between ions, including nucleobase cations despite their overall repulsive interactions. It is clear there is no correlation between EEML and Ees. However, strong relation between EEML and the charge penetration component of Ees is observed. The relation holds regardless of interaction types or whether or not interacting molecules bear the same or opposite charges. Thus, a charge density-based approach for computing intermolecular interaction energies and the atom–atom approach to analyse non-covalent interactions do complement each other, even in ionic systems. Full article
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Open AccessArticle
Pretreatment-Membrane Electrolysis Process for Treatment of Ammonium Sulfate Double Salt Crystals Formed During Electrolytic Manganese Production
Crystals 2019, 9(12), 667; https://doi.org/10.3390/cryst9120667 - 11 Dec 2019
Viewed by 124
Abstract
Ammonium sulfate double salt crystals (ASDSCs) are a by-product formed during the electrolytic production of manganese. The long-term open-air stacking of ASDSCs leads to the manganese and ammonia nitrogen present inside leaching with rainwater, which seriously damages the ecological environment. To find a [...] Read more.
Ammonium sulfate double salt crystals (ASDSCs) are a by-product formed during the electrolytic production of manganese. The long-term open-air stacking of ASDSCs leads to the manganese and ammonia nitrogen present inside leaching with rainwater, which seriously damages the ecological environment. To find a reasonable treatment method, we developed a pretreatment-membrane electrolysis method, which allowed for the recycling of ASDSCs stepwise. At the beginning, the ASDSCs were dissolved in water. The Mn2+ and Mg2+ present in the crystals were converted into MnCO3 and MgCO3 and recycled for the production of electrolytic manganese. The filtered liquid (mainly ammonium sulfate) was electrically decomposed to generate ammonia water and sulfuric acid, which were recycled for electrolytic manganese production. The results show that under the optimal conditions of a current density of 300 A/m2—an electrolysis time of 11 h and a temperature of 40 °C—the decomposition rate of ammonium sulfate reached 98.4%. This method led to the complete decomposition and utilization of the ASDSCs and truly achieved the green electrolytic production of manganese. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle
Enhancement of Intracavity-Pumped Terahertz Parametric Oscillator Power by Adopting Diode-Side Pumped Configuration Based on KTiOPO4 Crystal
Crystals 2019, 9(12), 666; https://doi.org/10.3390/cryst9120666 - 11 Dec 2019
Viewed by 157
Abstract
In this paper, a KTiOPO4 (KTP) crystal is used as the nonlinear medium in an intracavity-pumped terahertz parametric oscillator (TPO) based on stimulated polariton scattering (SPS). Almost all the reported intracavity SPS sources adopt the diode-end pumped configuration, and the THz output [...] Read more.
In this paper, a KTiOPO4 (KTP) crystal is used as the nonlinear medium in an intracavity-pumped terahertz parametric oscillator (TPO) based on stimulated polariton scattering (SPS). Almost all the reported intracavity SPS sources adopt the diode-end pumped configuration, and the THz output power is limited by the serious thermal effect and small fundamental beam size. For improving the THz output power, we propose diode-side pumping for the laser medium to get a higher fundamental power and a larger fundamental beam size. A convex–plane fundamental laser resonator is used to further offset the thermal effect and increase the fundamental beam size. The THz frequency of the intracavity-pumped KTP terahertz parametric oscillator can be discontinuously tuned from 3.19 THz to 5.94 THz with three gaps. The fundamental beam diameter in the KTP crystal is about 1.3 mm. The maximum average THz power is 166 μW at 5.74 THz under a pulse repetition frequency (PRF) of 6 kHz and a diode pump power of 98 W. By means of the diode-side pumped configuration, the maximum THz output power is more than two-fold higher compared to the diode-end pumped configuration reported using the KTP crystal. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle
Intermolecular Interactions in Molecular Organic Crystals upon Relaxation of Lattice Parameters
Crystals 2019, 9(12), 665; https://doi.org/10.3390/cryst9120665 - 10 Dec 2019
Viewed by 256
Abstract
Crystal structure prediction is based on the assumption that the most thermodynamically stable structure will crystallize first. The existence of other structures such as polymorphs or from counterenantiomers requires an accurate calculation of the electronic energy. Using atom-centered Gaussian basis functions in periodic [...] Read more.
Crystal structure prediction is based on the assumption that the most thermodynamically stable structure will crystallize first. The existence of other structures such as polymorphs or from counterenantiomers requires an accurate calculation of the electronic energy. Using atom-centered Gaussian basis functions in periodic Density Functional Theory (DFT) calculations in Turbomole, the performance of two dispersion-corrected functionals, PBE-D3 and B97-D, is assessed for molecular organic crystals of the X23 benchmark set. B97-D shows a MAE (mean absolute error) of 4 kJ/mol, compared to 9 kJ/mol for PBE-D3. A strategy for the convergence of lattice energies towards the basis set limit is outlined. A simultaneous minimization of molecular structures and lattice parameters shows that both methods are able to reproduce experimental unit cell parameters to within 4–5%. Calculated lattice energies, however, deviate slightly more from the experiment, i.e., by 0.4 kJ/mol after unit cell optimization for PBE-D3 and 0.5 kJ/mol for B97-D. The accuracy of the calculated lattice energies compared to the experimental values demonstrates the ability of current DFT methods to assist in the quest for possible polymorphs and enantioselective crystallization processes. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle
Coordination Assemblies of Zn(II) Coordination Polymers: Positional Isomeric Effect and Optical Properties
Crystals 2019, 9(12), 664; https://doi.org/10.3390/cryst9120664 - 10 Dec 2019
Viewed by 196
Abstract
Two Zn(II) coordination polymers (CPs) [Zn(L)(pphda)] (1) and [Zn(L)(ophda)]·H2O (2) were prepared by reactions of ZnSO4·7H2O based on the N-donor 1,4-di(1H-imidazol-4-yl)benzene (L) ligand and two flexible carboxylic acids isomers of 1,4-phenylenediacetic [...] Read more.
Two Zn(II) coordination polymers (CPs) [Zn(L)(pphda)] (1) and [Zn(L)(ophda)]·H2O (2) were prepared by reactions of ZnSO4·7H2O based on the N-donor 1,4-di(1H-imidazol-4-yl)benzene (L) ligand and two flexible carboxylic acids isomers of 1,4-phenylenediacetic acid (H2pphda) and 1,2-phenylenediacetic acid (H2ophda) as mixed ligands, respectively. Structures of CPs 1 and 2 were characterized by elemental analysis, Infrared spectroscopy (IR), thermogravimetric analysis and single-crystal X-ray diffraction. The CP 1 is a fourfold interpenetrating 66-diamond (dia) architecture, while 2 is a 2D (4, 4) square lattice (sql) layer based on the Zn2(cis-1,2-ophda2−)2 binuclear Zn(II) subunits. The luminescent property, including luminescence lifetime and quantum yield (QY), have been investigated for CPs 1 and 2. Full article
(This article belongs to the Special Issue Crystal Structure and Thermal Studies of Coordination Compounds)
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Open AccessArticle
Comparative Study of ZnO Nanostructures Grown on Variously Orientated GaN and AlxGa1−xN: The Role of Polarization, and Surface Pits
Crystals 2019, 9(12), 663; https://doi.org/10.3390/cryst9120663 - 09 Dec 2019
Viewed by 194
Abstract
:Through comparing ZnO directly grown on the substrates of a-plane, c-plane, and (11-22) plane GaN and AlxGa1−xN (0.06 ≤ x ≤ 1), the roles of different factors that may influence growth have been studied. Seeded by surface pits, ZnO [...] Read more.
:Through comparing ZnO directly grown on the substrates of a-plane, c-plane, and (11-22) plane GaN and AlxGa1−xN (0.06 ≤ x ≤ 1), the roles of different factors that may influence growth have been studied. Seeded by surface pits, ZnO nanowire (NW) preferentially grew along the polarized direction on top of the nonpolar GaN (laterally aligned), polar GaN and AlGaN (vertically aligned), and semipolar GaN (obliquely upward aligned). Nanosheets were easily formed when the polarized surface of the AlGaN film was not intact. The kinetic effect of polarization must be considered to explain the high aspect ratio of NWs along the polarized direction. It was found that dislocation affected NW growth through the surface pits, which provided excellent nucleation sites. If the surface pits on GaN could be controlled to distribute uniformly, self-organized ZnO NW array could be controllably and directly grown on GaN. Moreover, surface pits could also seed for nanosheet growth in AlN, since Al(OH)4 would presumably bind to the Zn2+ terminated surface and suppress the kinetic effects of polarization. Full article
(This article belongs to the Special Issue Dislocations in Heterostructures)
Open AccessArticle
Symmetric Fluoroborate and its Boron Modification: Crystal and Electronic Structures
Crystals 2019, 9(12), 662; https://doi.org/10.3390/cryst9120662 - 09 Dec 2019
Viewed by 163
Abstract
Four boron-carrying molecules were synthesized and purified. These were found to be (a) relatively neutral with respect to the parent BF derivative and (b) functionalized by donor–acceptor groups resulting in a charge transfer within the molecule. The study discusses the steric effect and [...] Read more.
Four boron-carrying molecules were synthesized and purified. These were found to be (a) relatively neutral with respect to the parent BF derivative and (b) functionalized by donor–acceptor groups resulting in a charge transfer within the molecule. The study discusses the steric effect and the influence of the substitution of the side rings on the surroundings of the boron atom. Electronic structures were characterized by real-space bonding indicators. Hirshfeld surface and energy frameworks tools were applied to examine the crystal packing features. Full article
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Open AccessArticle
Synthesis, X-ray Crystal Structure and Antimicrobial Activity of Unexpected Trinuclear Cu(II) Complex from s-Triazine-Based Di-Compartmental Ligand via Self-Assembly
Crystals 2019, 9(12), 661; https://doi.org/10.3390/cryst9120661 - 09 Dec 2019
Viewed by 180
Abstract
The synthesis and X-ray crystal structure of the trinuclear [Cu3(HL)(Cl)2(NO3)(H2O)5](NO3)2 complex of the s-triazine-based di-compartmental ligand, 2-methoxy-4,6-bis(2-(pyridin-2-ylmsethylene)hydrazinyl)-1,3,5-triazine (H2L), are presented. The Cu1 and Cu2 are [...] Read more.
The synthesis and X-ray crystal structure of the trinuclear [Cu3(HL)(Cl)2(NO3)(H2O)5](NO3)2 complex of the s-triazine-based di-compartmental ligand, 2-methoxy-4,6-bis(2-(pyridin-2-ylmsethylene)hydrazinyl)-1,3,5-triazine (H2L), are presented. The Cu1 and Cu2 are penta-coordinated with CuN3ClO coordination environment, distorted square pyramidal coordination geometry while Cu3 is hexa-coordinated with CuN2O4 coordination sphere, and distorted octahedral geometry. The complex crystallized in the primitive P-1 triclinic crystal system with two molecular units per unit cell. Its packing is dominated by the O–H (35.5%) and Cl–H (8.8%) hydrogen bonding interactions as well as the π–π stacking (2.3%) and anion–π-stacking interactions (3.7%). The different coordination interactions were analyzed using atoms in molecules (AIM) theory, and the number of charge transferences from the ligand group to Cu(II) were determined using natural bond orbital calculations. The effect of the free ligand and its Cu(II) complex on the tested pathogenic microbes (Staphylococcus aureus, S. epidermidis, Enterococcus faecalis, Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa) and one fungal isolate (Candida albicans) is presented. Both have wide spectrum antimicrobial activity against the selected microorganism. It is observed that the free ligand at 180 µg/mL was more effective than its Cu(II) complex and showed close results compared to the positive control gentamicin. At higher concentrations (1 mg/mL), the Cu(II) complex was found to be more active against S. epidermidis, E. coli and C. albicans than the lower concentration. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values are also lower for the Cu(II) complex than the free ligand. Full article
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Open AccessArticle
Crystallographic Insights into Uranyl Sulfate Minerals Formation: Synthesis and Crystal Structures of Three Novel Cesium Uranyl Sulfates
Crystals 2019, 9(12), 660; https://doi.org/10.3390/cryst9120660 - 09 Dec 2019
Viewed by 138
Abstract
An alteration of the uranyl oxide hydroxy-hydrate mineral schoepite [(UO2)8O2(OH)12](H2O)12 at mild hydrothermal conditions was studied. As the result, four different crystalline phases Cs[(UO2)(SO4)(OH)](H2O)0.25 ( [...] Read more.
An alteration of the uranyl oxide hydroxy-hydrate mineral schoepite [(UO2)8O2(OH)12](H2O)12 at mild hydrothermal conditions was studied. As the result, four different crystalline phases Cs[(UO2)(SO4)(OH)](H2O)0.25 (1), Cs3[(UO2)4(SO4)2O3(OH)](H2O)3 (2), Cs6[(UO2)2(SO4)5](H2O)3 (3), and Cs2[(UO2)(SO4)2] (4) were obtained, including three novel compounds. The obtained Cs uranyl sulfate compounds 1, 3, and 4 were analyzed using single-crystal XRD, EDX, as well as topological analysis and information-based structural complexity measures. The crystal structure of 3 was based on the 1D complex, the topology of which was unprecedented for the structural chemistry of inorganic oxysalts. Crystal chemical analysis performed herein suggested that the majority of the uranyl sulfates minerals were grown from heated solutions, and the temperature range could be assumed from the manner of interpolyhedral linkage. The presence of edge-sharing uranyl bipyramids most likely pointed to the temperatures of higher than 100 °C. The linkage of sulfate tetrahedra with uranyl polyhedra through the common edges involved elevated temperatures but of lower values (~70–100 °C). Complexity parameters of the synthetic compounds were generally lower than that of uranyl sulfate minerals, whose structures were based on the complexes with the same or genetically similar topologies. The topological complexity of the uranyl sulfate structural units contributed the major portion to the overall complexity of the synthesized compounds, while the complexity of the respective minerals was largely governed by the interstitial structure and H-bonding system. Full article
(This article belongs to the Special Issue Mineralogical Crystallography)
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Open AccessArticle
Design of a Bicycle Head Lamp Using an Atypical White Light-Emitting Diode with Separate Dies
Crystals 2019, 9(12), 659; https://doi.org/10.3390/cryst9120659 - 09 Dec 2019
Viewed by 150
Abstract
To the best of our knowledge, this is the first demonstration of a design for a bicycle head lamp with a high-contrast cutoff line using an atypical white light-emitting diode (LED) with two separate dies. The precise optical model was created by setting [...] Read more.
To the best of our knowledge, this is the first demonstration of a design for a bicycle head lamp with a high-contrast cutoff line using an atypical white light-emitting diode (LED) with two separate dies. The precise optical model was created by setting the weighting factor on the emitting surface. The downward reflector was designed and fabricated to produce a high-contrast cutoff line in both short- and long-axis orientations, but a yellowish outer pattern was observed. A modified two-color optical model was created to describe the yellowish patterns in both orientations and explain the yellowish effect. Such an effect was caused by the larger coverage area of the phosphor than that by the blue dies. To reduce the yellowish effect near the cutoff line, a specific phosphor area was blocked in the experiment. The yellowish effect was greatly reduced, and the contrast across the cutoff line was enhanced. The presented technology is useful for designing a high-contrast light pattern with such an atypical white LED. Full article
(This article belongs to the Special Issue Advanced LED Solid-state Lighting Optics)
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Open AccessArticle
High Efficient YVPO4 Luminescent Materials Activated by Europium
Crystals 2019, 9(12), 658; https://doi.org/10.3390/cryst9120658 - 09 Dec 2019
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Abstract
YPO4:Eu, YVO4:Eu, and YVPO4:Eu based phosphors with various Eu(III) activator contents and phosphate-vanadate ratios were synthesized by the self-propagating high-temperature synthesis method. The samples were characterized by scanning electron microscopy, nitrogen sorption, acid-base indicators and photoluminescence. The [...] Read more.
YPO4:Eu, YVO4:Eu, and YVPO4:Eu based phosphors with various Eu(III) activator contents and phosphate-vanadate ratios were synthesized by the self-propagating high-temperature synthesis method. The samples were characterized by scanning electron microscopy, nitrogen sorption, acid-base indicators and photoluminescence. The particle surface features with a finely dispersed structure comprising all the involved elements. The pore structure and the specific surface areas of the samples were different depending on the compositions of the samples. The most finely dispersed sample was YVO4:Eu samples. The specific surface areas of the YPO4:Eu samples were 10 to 15 times greater than those of vanadate samples. The phosphors samples had a slightly basic (YVO4:Eu, YVPO4:Eu) or slightly acidic (YPO4:Eu) properties of the surface with different contents of Lewis and Brönsted sites. The differences in the compositions and acid-base state resulted in the difference in the intensity and brightness of the photoluminescence (PL) of the samples. The yttrium-phosphate-vanadate phosphors of the mixed YVxP1−xO4-Eu had higher brightness and PL intensity than those samples with similar phosphate as well as vanadate phosphors. Full article
(This article belongs to the Special Issue Synthesis and Characterization of Lanthanide Complexes)
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Open AccessArticle
Synthesis, Single Crystal X-Ray Structure, Theoretical Studies of Triple-{MnIII-Schiff-Base}-Decorated Molybdate
Crystals 2019, 9(12), 657; https://doi.org/10.3390/cryst9120657 - 09 Dec 2019
Viewed by 166
Abstract
The design and synthesis of magnets with low dimensionality is currently an attractive research topic. The reaction of a Schiff base metal complex with simple molybdate has led to the formation of a new {MnIII-Schiff-base}-decorated molybdate heterometallic cluster, [{Mn(salpn)(H2O)} [...] Read more.
The design and synthesis of magnets with low dimensionality is currently an attractive research topic. The reaction of a Schiff base metal complex with simple molybdate has led to the formation of a new {MnIII-Schiff-base}-decorated molybdate heterometallic cluster, [{Mn(salpn)(H2O)}3MoO4](CH3COO)·2H2O (1) (salpn = N,N’-(1,3-propylene)bis(salicylideneiminate)). The hybrid aggregate was characterized using a range of methods including elemental analysis, single crystal x-ray diffraction, Infrared spectra (IR) spectroscopy, and x-ray structural analysis. The crystals of 1 are hexagonal: P63/m, a = 14.027(5) Å, c = 17.487(5) Å, V = 1142.6(3) Å3. Structural analyses indicate that we report on the preparation of the first triple metallic-oligomer held by orthomolybdate. Density functional theoretical calculation (DFT) studies have been performed to calculate electronic structure and potential energy landscapes. Additionally, the magnetic property of 1 indicates an antiferromagnetic coupling between the metal centers in the complex. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle
Crystal Structure of Bacterial Cystathionine Γ-Lyase in The Cysteine Biosynthesis Pathway of Staphylococcus aureus
Crystals 2019, 9(12), 656; https://doi.org/10.3390/cryst9120656 - 09 Dec 2019
Viewed by 203
Abstract
Many enzymes require pyridoxal 5’-phosphate (PLP) as an essential cofactor and share active site residues in mediating diverse enzymatic reactions. Methionine can be converted into cysteine by cystathionine γ-lyases (CGLs) through a transsulfuration reaction dependent on PLP. In bacteria, MccB, also known as [...] Read more.
Many enzymes require pyridoxal 5’-phosphate (PLP) as an essential cofactor and share active site residues in mediating diverse enzymatic reactions. Methionine can be converted into cysteine by cystathionine γ-lyases (CGLs) through a transsulfuration reaction dependent on PLP. In bacteria, MccB, also known as YhrB, exhibits CGL activity that cleaves the C–S bond of cystathionine at the γ position. In this study, we determined the crystal structure of MccB from Staphylococcus aureus in its apo- and PLP-bound forms. The structures of MccB exhibited similar molecular arrangements to those of MetC-mediating β-elimination with the same substrate and further illustrated PLP-induced structural changes in MccB. A structural comparison to MetC revealed a longer distance between the N-1 atom of the pyridine ring of PLP and the Oδ atom of the Asp residue, as well as a wider and more flexible active site environment in MccB. We also found a hydrogen bond network in Ser-water-Ser-Glu near the Schiff base nitrogen atom of the PLP molecule and propose the Ser-water-Ser-Glu motif as a general base for the γ-elimination process. Our study suggests the molecular mechanism for how homologous enzymes that use PLP as a cofactor catalyze different reactions with the same active site residues. Full article
(This article belongs to the Special Issue Crystallographic Studies of Enzymes)
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Open AccessArticle
Comparative Study on AC Susceptibility of YBa2Cu3O7−δ Added with BaZrO3 Nanoparticles Prepared via Solid-State and Co-Precipitation Method
Crystals 2019, 9(12), 655; https://doi.org/10.3390/cryst9120655 - 09 Dec 2019
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Abstract
Polycrystalline samples of YBa2Cu3O7−δ (Y-123) added with x mol% of BaZrO3 (BZO) nanoparticles (x = 0.0, 2.0, 5.0, and 7.0) were synthesized using co-precipitation (COP) and solid-state (SS) method. X-ray diffraction (XRD) patterns showed the formation [...] Read more.
Polycrystalline samples of YBa2Cu3O7−δ (Y-123) added with x mol% of BaZrO3 (BZO) nanoparticles (x = 0.0, 2.0, 5.0, and 7.0) were synthesized using co-precipitation (COP) and solid-state (SS) method. X-ray diffraction (XRD) patterns showed the formation of Y-123 and Y-211 as the major and minor phases, respectively. The samples prepared using COP method showed higher weight percentage of Y-123 phase (≤98%) compared to the SS samples (≤93%). A peak corresponding to BZO was also found in the samples added with BZO nanoparticles. The increasing intensity of the BZO peak as the BZO amount increased showed the increasing amount of the unreacted nanoparticles in the samples. Refinement of unit cell lattice parameters indicated that all the samples have an orthorhombic crystal structure and there is no orthorhombic-tetragonal phase transformation. As observed using scanning electron microscopy (SEM), all the samples showed randomly distributed grains with irregular shape. The average grain size for the pure sample prepared using COP method is smaller (0.30 µm) compared with that of the pure SS sample (1.24 µm). Addition of 7.0 mol% BZO led to an increase of average grain size to 0.50 μm and 2.71 μm for the COP and SS samples, respectively, indicating grain growth. AC susceptibility (ACS) measurement showed a decrease in the onset critical temperature, Tc-onset with BZO addition. Comparatively, Tc-onset for the COP samples is higher than that of the SS samples. The value of Josephson’s current, Io increased up to 2.0 mol% BZO addition, above which the Io decreased more drastically for the SS samples. The value of Io is 53.95 μA and 32.08 μA for the 2.0 mol% BZO added SS and COP samples, respectively. The decrease of Io is attributed to the distribution of BZO particles at the grain boundaries as also reflected in the drastic decrease of phase lock-in temperature, Tcj. As a result of smaller average grain size, the presence of more grain boundaries containing insulating BZO particles led to lower Io in the COP samples. Full article
(This article belongs to the Special Issue Synthesis and Characterization of New Superconductors Materials)
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Open AccessArticle
Synthesis and Characterization of (Ca,Sr)[C2O4]∙nH2O Solid Solutions: Variations of Phase Composition, Crystal Morphologies and in Ionic Substitutions
Crystals 2019, 9(12), 654; https://doi.org/10.3390/cryst9120654 - 08 Dec 2019
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Abstract
To study strontium (Sr) incorporation into calcium oxalates (weddellite and whewellite), calcium-strontium oxalate solid solutions (Ca,Sr)[C2O4]∙nH2O (n = 1, 2) are synthesized and studied by a complex of methods: powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) [...] Read more.
To study strontium (Sr) incorporation into calcium oxalates (weddellite and whewellite), calcium-strontium oxalate solid solutions (Ca,Sr)[C2O4]∙nH2O (n = 1, 2) are synthesized and studied by a complex of methods: powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Two series of solid solutions, isomorphous (Ca,Sr)[C2O4]·(2.5 − x)H2O) (space group I4/m) and isodimorphous Ca[C2O4]·H2O(sp.gr. P21/c)–Sr[C2O4]·H2O(sp.gr. P 1 - ), are experimentally detected. The morphogenetic regularities of their crystallization are revealed. The factors controlling this process are discussed. Full article
(This article belongs to the Special Issue Mineralogical Crystallography)
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Open AccessArticle
Improvement of Growth Interface Stability for 4-Inch Silicon Carbide Crystal Growth in TSSG
Crystals 2019, 9(12), 653; https://doi.org/10.3390/cryst9120653 - 07 Dec 2019
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Abstract
The growth interface instability of large-size SiC growth in top-seeded solution growth (TSSG) is a bottleneck for industrial production. The authors have previously simulated the growth of 4-inch SiC crystals and found that the interface instability in TSSG was greatly affected by the [...] Read more.
The growth interface instability of large-size SiC growth in top-seeded solution growth (TSSG) is a bottleneck for industrial production. The authors have previously simulated the growth of 4-inch SiC crystals and found that the interface instability in TSSG was greatly affected by the flow field. According to our simulation of the flow field, we proposed a new stepped structure that greatly improved the interface stability of large-size crystal growth. This stepped structure provides a good reference for the growth of large-sized SiC crystals by TSSG in the future. Full article
(This article belongs to the Special Issue Crystal Growth from Liquid Phase)
Open AccessArticle
Bending Nanoindentation and Plasticity Noise in FCC Single and Polycrystals
Crystals 2019, 9(12), 652; https://doi.org/10.3390/cryst9120652 - 07 Dec 2019
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Abstract
We present a high-throughput nanoindentation study of in situ bending effects on incipient plastic deformation behavior of polycrystalline and single-crystalline pure aluminum and pure copper at ultranano depths (< 200 nm). We find that hardness displays a statistically inverse dependence on in-plane stress [...] Read more.
We present a high-throughput nanoindentation study of in situ bending effects on incipient plastic deformation behavior of polycrystalline and single-crystalline pure aluminum and pure copper at ultranano depths (< 200 nm). We find that hardness displays a statistically inverse dependence on in-plane stress for indentation depths smaller than 10 nm, and the dependence disappears for larger indentation depths. In contrast, plastic noise in the nanoindentation force and displacement displays statistically robust noise features, independently of applied stresses. Our experimental results suggest the existence of a regime in Face Centered Cubic (FCC) crystals where ultranano hardness is sensitive to residual applied stresses, but plasticity pop-in noise is insensitive to it. Full article
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Open AccessArticle
Origin of Nanoscale Incipient Plasticity in GaAs and InP Crystal
Crystals 2019, 9(12), 651; https://doi.org/10.3390/cryst9120651 - 07 Dec 2019
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Abstract
In this article, we exhibit the influence of doping on nanoindentation-induced incipient plasticity in GaAs and InP crystals. Nanoindentation experiments carried out on a GaAs crystal show a reduction in contact pressure at the beginning of the plastic deformation caused by an increase [...] Read more.
In this article, we exhibit the influence of doping on nanoindentation-induced incipient plasticity in GaAs and InP crystals. Nanoindentation experiments carried out on a GaAs crystal show a reduction in contact pressure at the beginning of the plastic deformation caused by an increase in Si doping. Given that the substitutional Si defects cause a decrease in the pressure of the GaAs-I → GaAs-II phase transformation, we concluded that the elastic–plastic transition in GaAs is a phase-change-driven phenomenon. In contrast, Zn- and S-doping of InP crystals cause an increase in contact pressure at the elastic–plastic transition, revealing its dislocation origin. Our mechanical measurements were supplemented by nanoECR experiments, which showed a significant difference in the flow of the electrical current at the onset of plastic deformation of the semiconductors under consideration. Full article
(This article belongs to the Special Issue Dislocations in Heterostructures)
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Open AccessArticle
Liquid Crystal-Based Enclosed Coplanar Waveguide Phase Shifter for 54–66 GHz Applications
Crystals 2019, 9(12), 650; https://doi.org/10.3390/cryst9120650 - 06 Dec 2019
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Abstract
A 0–10 V bias voltage-driven liquid crystal (LC) based 0°–180° continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than −4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed [...] Read more.
A 0–10 V bias voltage-driven liquid crystal (LC) based 0°–180° continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than −4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed coplanar waveguide (ECPW) with LC as tunable dielectrics encapsulated by a unified ground plate in the design, which significantly reduced the instability due to floating effects and losses due to stray modes. By competing for spatial volume distribution of the millimeter-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics, the ECPW’s geometry and materials are optimized to minimize the total of dielectric volumetric loss and metallic surface loss for a fixed phase-tuning range. The optimized LC-based ECPW was impedance matched with 1.85 mm connectors by the time domain reflectometry (TDR) method. Device fabrication featured the use of rolled annealed copper foil of lowest surface roughness with nickel-free gold-plating of optimal thickness. Measured from 54 GHz to 66 GHz, the phase shifter prototype presented a tangible improvement in phase shift effectiveness and signal-to-noise ratio, while exhibiting lower insertion and return losses, more ease of control, and high linearity as well as lower-cost fabrication as compared with up-to-date documentations targeting 60 GHz applications. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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Open AccessArticle
Isomorphous Crystals Formed by the Similar Supramolecular Motifs in Sorafenib Hydrochloride and Regorafenib Hydrochloride Salts
Crystals 2019, 9(12), 649; https://doi.org/10.3390/cryst9120649 - 06 Dec 2019
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Abstract
Sorafenib and regorafenib (or fluoro-sorafenib) are multikinase inhibitors active in the treatment of various human cancers, but their solubilities are very poor. To improve their solubilities, in this study, sorafenib hydrochloride (Sor·HCl, I) and regorafenib hydrochloride (Reg·HCl, II) have been prepared and their [...] Read more.
Sorafenib and regorafenib (or fluoro-sorafenib) are multikinase inhibitors active in the treatment of various human cancers, but their solubilities are very poor. To improve their solubilities, in this study, sorafenib hydrochloride (Sor·HCl, I) and regorafenib hydrochloride (Reg·HCl, II) have been prepared and their crystal structures were characterized. Their solubility properties in water were evaluated. Intriguingly, they are isomorphous crystal structures with the same space group and the similar unit cell dimensions, which were caused by the similar supramolecular patterns resulted by the formation of N–H···Cl hydrogen bond instead of hydrogen bond between the protonated pyridinium cation and counterion. Moreover, the solubility properties displayed identical profiles. It may be concluded that a similar crystal structure leads to a comparable solubility profile. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals and Its Application)
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Effect of Ag/rGO on the Optical Properties of Plasmon-Modified SnO2 Composite and Its Application in Self-Powered UV Photodetector
Crystals 2019, 9(12), 648; https://doi.org/10.3390/cryst9120648 - 06 Dec 2019
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Abstract
A facile hydrothermal method was employed to synthesize silver–reduced graphene oxide (Ag/rGO) plasmon-modified SnO2 composite, by incorporating Ag–reduced graphene oxide (Ag/rGO) into SnO2 nanorods as a photoanode for assembling a self-powered ultraviolet photodetector (UVPD). The as-synthesized samples were investigated in detail [...] Read more.
A facile hydrothermal method was employed to synthesize silver–reduced graphene oxide (Ag/rGO) plasmon-modified SnO2 composite, by incorporating Ag–reduced graphene oxide (Ag/rGO) into SnO2 nanorods as a photoanode for assembling a self-powered ultraviolet photodetector (UVPD). The as-synthesized samples were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and UV visible spectrophotometer. The as-prepared Ag/rGO films show enhanced light absorption attributed to the localized surface plasmon resonance (LSPR). The optimized 1.0 wt.% Ag/rGO incorporated into SnO2-based UVPD exhibits a significant photocurrent response due to the enhanced absorption light and effective suppression of charge recombination. This UVPD demonstrates a high performance, with photocurrent density reaching 0.29 mAcm−2 compared to the SnO2-based device with 0.16 mAcm−2. This device also exhibits a high on:off ratio of 195 and fast response time, which are superior to that of the free-modified one. In addition, the UVPD based on plasmon-modified SnO2 photoanode treated with TiCl4-aqueous solution has attained a higher photocurrent with a maximum value reaching 5.4 mAcm−2, making this device favorable in ultraviolet detection. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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Open AccessArticle
Crystallization of CaCO3 in Aqueous Solutions with Extremely High Concentrations of NaCl
Crystals 2019, 9(12), 647; https://doi.org/10.3390/cryst9120647 - 06 Dec 2019
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Abstract
The effect of NaCl at extremely high concentrations from 3.5 to 14 wt. % on the crystallization of CaCO3 was investigated in depth. The static test experiment verified that the Ca2+ retention efficiency (η) of NaCl on CaCO3 [...] Read more.
The effect of NaCl at extremely high concentrations from 3.5 to 14 wt. % on the crystallization of CaCO3 was investigated in depth. The static test experiment verified that the Ca2+ retention efficiency (η) of NaCl on CaCO3 scale increased from 31.06% (3.5 wt. %) to 41.56% (14 wt. %). Based on the calculation of supersaturation rations, the high concentration of NaCl could reduce the activity coefficients of [Ca2+] and [CO32−], thus reducing the actual concentration of CaCO3. The CaCO3 deposition rate constants (k) showed that NaCl slowed down the rate of CaCO3 crystallization. The X–ray diffraction (XRD) testing disclosed that the growth of (1 0 4) and (1 1 0) faces from calcite was impeded, while the formation of (1 1 1) face from aragonite was induced by the increasing concentration of NaCl. The inductively coupled plasma optical emission spectrometry (ICP–OES) results indicated that Na+ could be doped into CaCO3, leading to the one–dimensional crystal growth. It was further proved that NaCl heightens the efficiency of the typical phosphate inhibitors (2–phosphonobutane–1,2,4–tricarboxylic acid (PBTCA) and 1–hydroxyethane–1,1–diphosphonic acid (HEDP)) on prohibiting the scale of CaCO3. Full article
(This article belongs to the Special Issue Carbonates Volume II)
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Open AccessArticle
Growth of KDP: Fe3+ Crystals from Oversaturated Aqueous Solutions
Crystals 2019, 9(12), 646; https://doi.org/10.3390/cryst9120646 - 05 Dec 2019
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Abstract
The KH2PO4 solubility curves in pure water and in water with the addition of 50 ppm Fe3+ were refined. The KH2PO4 and KH2PO4: Fe3+ solutions stability to supercooling was evaluated by [...] Read more.
The KH2PO4 solubility curves in pure water and in water with the addition of 50 ppm Fe3+ were refined. The KH2PO4 and KH2PO4: Fe3+ solutions stability to supercooling was evaluated by polythermal studies of the width of metastable zone. It was shown that Fe3+ addition makes the solution more stable. A series of Fe3+ doped KDP crystals were grown at different temperature and hydrodynamic regimes at supersaturation level up to 0.45. Their real structure was studied by X-ray projection topography and, as a result, the most suitable growth conditions are chosen. The transmittance spectra of prism sectors with ferric iron concentrations CFe up to 102 ppm were obtained. It was found that KDP crystals with CFe >60 ppm can be used as optical filters for suppressing transmission in UV-C and UV-B ranges. Full article
(This article belongs to the Special Issue Crystal Growth from Liquid Phase)
Open AccessArticle
Research on Luminance Distributions of Chip-On-Board Light-Emitting Diodes
Crystals 2019, 9(12), 645; https://doi.org/10.3390/cryst9120645 - 05 Dec 2019
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Abstract
Chip-On-Board Light-Emitting Diodes (COB LED) are increasingly more common. Their development in recent years has directly contributed to increasing the power of LED sources, whilst simultaneously increasing the luminous flux from the entire COB. Consequently, it has led to new developments in some [...] Read more.
Chip-On-Board Light-Emitting Diodes (COB LED) are increasingly more common. Their development in recent years has directly contributed to increasing the power of LED sources, whilst simultaneously increasing the luminous flux from the entire COB. Consequently, it has led to new developments in some applications. Information regarding the size of the light source luminous surface and luminance distribution on its surface is critical for a designer whilst designing optical systems. The purpose of this conducted research was to establish to what extent luminance distribution is even on the examined COB LEDs. In order to verify luminance distributions on an LED surface, direct measurements with a matrix luminance measuring device were made. As a result of the research, it has been observed that luminance distribution is not even, and in many cases luminance maximum does not fall in the geometric center of the luminous surface, which was initially expected. So, it has been concluded that while designing optical systems for COB LEDs, irregular luminance distribution on their surface needs to be considered. Full article
(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))
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