Decrease In Peak Intensity Research Articles

Study on mechanical properties and statistical damage constitutive model of red sandstone after heating and water-cooling cycles

The repeated action of high temperature and water cooling will have a strong deteriorating effect on the mechanical properties of the rock, which will eventually lead to the damage and cracking of the rock. In order to study the influence of heating and water-cooling cycles on rocks, the P-wave velocity and mechanical properties of red sandstone after heating and water-cooling cycles were tested. Meanwhile, based on the Weibull distribution theory, a statistical damage constitutive model based on Mohr-Coulomb strength criterion considering the effects of heating and water-cooling cycles was established, and verified based on the results of triaxial tests. The results show that the P-wave velocity and peak intensity decrease with the temperature under the same number of cycles. The elastic modulus will decrease with the temperature and the number of cycles, indicating that the red sandstone will gradually soften and the ductility will increase under repeated high temperature and water-cooling cycles. And the model can well reflect the stress-strain curves of different high temperature and water-cooling cycles. The research results can provide analytical theories and methods for geothermal development projects.

Synthesis, characterization and thermal behavior of plasticized poly (vinyl chloride) doped with folic acid-modified titanium dioxide

To inhibit the agglomeration of nanotitanium dioxide, a poly (vinyl chloride) (PVC) composite film doped with folic acid-modified titanium dioxide was synthesized and characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy and thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The average grain size of the folic acid-modified titanium dioxide was found to decrease by 1.3 nm, indicating that the cohesiveness of the nanoparticles is decreased. The lowest temperature for 1.0% thermal decomposition of PVC was determined to be 230.0 °C. The decomposition rate at the peak temperature is found to be 39.6% lower than that of a control sample. The stability of the PVC is improved due to a lower number of surface chlorine atoms as well intermolecular attraction. A mechanism for folic acid modification of titanium dioxide-doped PVC is proposed. After doping, the ester groups in the plasticizer show a significant decrease in the vibration peak intensities observed at 1264 cm−1, 1736 cm−1 and 1106 cm−1. The doped PVC film suppresses the release of CO2, and the strongest vibration peak at 1264 cm−1 is found to be 17.2% lower than that for the blank sample, indicating that doping is beneficial for plasticizer recovery.

Effect of curing temperature in the relative decrease peak intensity of calcium hydroxide pastes for assessing pozzolanicity of supplementary cementitious materials

Among the short-term viable alternatives for mitigating the direct emissions of carbon dioxide into the atmosphere by the cement industry, the partial replacement of Portland clinker or cement with supplementary cementitious materials (SCM) is the most efficient and conceives ecologically friendly binders. Limitations of available traditional SCMs create a demand for the exploration of alternative materials from by-products and wastes of other industries. As a result of the considerable variability in the properties between batches of these materials, it is necessary to use methods that allow the large-scale evaluation of SCMs in a fast, practical, reliable, and robust manner. This study presents the effects of increasing the curing temperature in the acceleration of the relative decrease in peak intensity (RDPI) test. The results show that samples cured at 65 °C after 3 days presented RDPI with a good indication of the reactivity level of the analyzed pozzolans. Additionally, strong correlations (R2 > 0.90) are obtained with compressive strength at 28 and 90 days. Thus, the RDPI test presents a potential for evaluating pozzolanic reactivity. However, further study is required on the SCM to CH ratio to avoid limiting the effectiveness of highly reactive pozzolans.

Influence of 60Co gamma irradiation on the structural and optical properties of 2-aminopyridinium 4-nitrophenolate 4-nitrophenol crystals

In this article, effect of gamma irradiation on the structural and optical properties of 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) has been reported. The grown crystals of 2AP4N were exposed to 60Co gamma rays with a dose of 50 kGy and 100 kGy. The radiation-induced effects were analyzed using X-ray diffraction, FT-IR, UV–visible, photoluminescence techniques. The refractive index was determined using a long arm spectrometer. The structural properties of the pristine and irradiated crystals were studied using powder XRD. The peak intensity decrease after irradiation may be attributed to the formation of point defects. The UV visible study reveals that the energy gap has decreased after irradiation and then has increased for the higher dose. The intensity variation in the PL spectra is due to colour center mechanism. The SHG efficiency of 2AP4N crystals was found to be unaffected by gamma irradiation.

Utilization of chestnut shell lignin in alginate films.

Lignocellulosic structures obtained from agricultural wastes can re-design sustainable packaging materials. The present study investigated the utilization of lignocellulose (LS), alkali lignin (L) and hydroxymethylated (modified) lignin (ML), separated from chestnut shells in alginate (AL) films at 100 and 200 mg g-1 (10% and 20%, w/w based on AL), as reinforcing agents. Lignin modification and concentration effects on the AL films were characterized by water vapor permeability (WVP), as well as morphological, mechanical, optical, thermal and active properties. Fourier transform infrared spectroscopy results showed that extracted L and LS had different structures, and the modification of L resulted in a peak shift and a decrease in peak intensities between 1250 and 800 cm-1 . The antioxidant and antimicrobial activity tests showed that films containing L had higher activity values (P < 0.05). WVP of the films containing ML was the lowest (P < 0.05) and the results revealed that 20% (w/w) concentration had an adverse effect on the WVP of films. The addition of L, LS and ML increased the tensile strength, elastic modulus and thermal properties (P < 0.05) compared to AL control films. With an increasing concentration, films containing L-based structures showed higher opacity and relatively lower L* values (P < 0.05). These results show that the addition of lignin to biopolymers is a promising method for improving the properties of biopolymers and providing functional attributes. LS had no or little effect on the film properties; however, the modification of L had the advantage of enhancing WVP and thermal properties at the same time as showing a decrease in functional properties compared to L. © 2022 Society of Chemical Industry.

Highly ordered pure and indium-incorporated MCM-41 mesoporous adsorbents: synthesis, characterization and evaluation for dye removal

Highly ordered pure MCM-41 and In-MCM-41 mesoporous adsorbents (with Si/In = 95 (IM0.05) and Si/In = 90 (IM0.1)) were synthesized using the hydrothermal-assisted method. The structural, morphological and texture characteristics were investigated by XRD, N2 adsorption–desorption, SEM-EDX, TEM, diffuse reflectance (DR) and FTIR. The broadening XRD diffraction peaks as well as the shifts to higher and lower 2-theta in IM0.05 and IM0.1, respectively, confirmed the incorporation of indium atoms in the MCM-41 structure. SEM-EXD and TEM images showed that pure MCM-41 and IM0.05 preserve a highly long-range well-ordered hexagonal pore structure, on the other hand, high loading of indium (IM0.1) resulted in partially irregular pore-ordering and morphological defects related to a partial dissolution of MCM-41 structure. The infrared spectra of In-incorporated samples showed a decrease in the transmittance intensity of MCM-41 characteristic peaks with little shifts relative to the pure MCM-41 sample. The potential of pure MCM-41 and In-MCM-41 samples for adsorption of dyes was preliminarily investigated. The removal efficiency of both methylene blue and basic yellow-28 (BY28) was enhanced by the incorporation of indium in the MCM-41. The adsorption equilibrium data of BY28 dye on pure, IM0.05 and IM0.1 samples fitted well with Langmuir adsorption model with adsorption capacity of 123.46, 156.99 and 158.48 mg g−1 respectively. The calculated free adsorption energy obtained from D–R isotherm was found to be 26.7 kJ mol−1 referring to that the adsorption of BY28 on IM0.05 adsorbent is chemical. The adsorption kinetic of BY28 on IM0.05 sample followed the pseudo-second-order model. The adsorption experiments revealed that the prepared samples can be used as effective adsorbents for the removal of dyes in aqueous solutions with good recovery and recyclability.Graphical

Catalytic Sulfation of Betulin with Sulfamic Acid: Experiment and DFT Calculation.

Betulin is an important triterpenoid substance isolated from birch bark, which, together with its sulfates, exhibits important bioactive properties. We report on a newly developed method of betulin sulfation with sulfamic acid in pyridine in the presence of an Amberlyst®15 solid acid catalyst. It has been shown that this catalyst remains stable when being repeatedly (up to four cycles) used and ensures obtaining of sulfated betulin with a sulfur content of ~10%. The introduction of the sulfate group into the betulin molecule has been proven by Fourier-transform infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopy. The Fourier-transform infrared (FTIR) spectra contain absorption bands at 1249 and 835–841 cm−1; in the UV spectra, the peak intensity decreases; and, in the nuclear magnetic resonance (NMR) spectra, of betulin disulfate, carbons С3 and С28 are completely shifted to the weak-field region (to 88.21 and 67.32 ppm, respectively) with respect to betulin. Using the potentiometric titration method, the product of acidity constants K1 and K2 of a solution of the betulin disulfate H+ form has been found to be 3.86 × 10–6 ± 0.004. It has been demonstrated by the thermal analysis that betulin and the betulin disulfate sodium salt are stable at temperatures of up to 240 and 220 °C, respectively. The density functional theory method has been used to obtain data on the most stable conformations, molecular electrostatic potential, frontier molecular orbitals, and mulliken atomic charges of betulin and betulin disulfate and to calculate the spectral characteristics of initial and sulfated betulin, which agree well with the experimental data.

Effect of gamma irradiation on the physicochemical properties of sodium alginate solution and internally crosslinked film made thereof

Research on using natural origin polymers as substitutes for petroleum-based plastics has been around for years owning to their renewable and sustainable characteristics. The use of ionizing radiation such as gamma (γ) rays for structural modification of natural polymers could broaden its application while protecting the environment. This study investigated the effect of γ-irradiation on the physicochemical properties of sodium alginate solution (SAS) and sodium alginate film (SAF) made thereof. The SAS was irradiated at 0 (control), 5, 10, 20, and 40 kGy before SAF was synthesized. Thermogravimetric analysis (TGA) revealed that the thermal stability of SAS decreased following the first-order degradation kinetics with every two-fold increment in γ-irradiation dose. Fourier transform infrared spectroscopy (FTIR) showed a decrease in the carbonyl group peak intensity for both SAS and SAF as the γ-irradiation dose increased. The critical dose to cause a significant decrease in the molecular weight of SA was determined to be 5 kGy. The water vapor permeability of SAF made using SAS irradiated up to 10 kGy improved by approximately 17% as compared with the control. Overall, this study contributed fundamental knowledge on sodium alginate chain modification induced by γ-irradiation and proposed that irradiated sodium alginate is a promising starting material for the synthesis of biopolymer film.

Effect of Fe Doping on Photocatalytic Dye-Degradation and Antibacterial Activity of SnO2 Nanoparticles

A simple hydrothermal method is utilized to synthesize iron-doped tin oxide nanoparticles (Fe-SnO2 NPs) at various doping concentrations. The structural characterization using XRD, Raman, and FTIR measurements confirmed the incorporation of Fe ions into the SnO2 lattice without any deviation in the tetragonal crystal system of SnO2 nanoparticles. SEM and HRTEM images show the spherical-shaped nanoparticles with agglomeration. The values of interplanar spacing ([Formula: see text]-value) calculated from the HRTEM lattice are consistent with the XRD results. Further, optical analysis revealed a red shift in the optical absorption band and a decrease in the band gap energy with an increase in Fe-dopant concentration. The decrease of PL emission peak intensity with Fe doping revealed the generation of singly charged oxygen vacancies. The H2O2-assisted photocatalytic degradation efficiency of Fe-SnO2 NPs investigated against crystal violet dye indicated an efficiency of 98% for 0.05 M Fe-SnO2 NPs within 30 minutes under visible light illumination. In addition, the effects of pH, scavengers, and reusability of the catalyst are tested. The antibacterial behavior of Fe-SnO2 NPs against Escherichia coli is examined by using the colony count method, and the inhibition rate was found to be 49, 65, 70, and 78% for pure, 0.01, 0.03, and 0.05 M Fe-SnO2 NPs, respectively.

Analytical Formula to Investigate the Modulation of Sloped Targets Using LiDAR Waveform

The relationship between the properties of targets and the features of modulated waveforms is fundamental to remote sensing based on the full-waveform light detection and ranging (LiDAR). Developing a mathematical formula of modulated LiDAR waveforms is of great importance in establishing this relationship. In this study, we derive the mathematical formula of a laser echo waveform modulated by four typical targets: a rectangle, a square, a circle, and an equilateral triangle. By using these formulas, numerical calculations are performed to investigate the relationship between the properties of the targets and the features of the modulated waveform. The results show that, at a rotation angle of 80°, the modulated waveform changes from a Gaussian form to a non-Gaussian form and finally returns to a Gaussian form as the target size increases. When the target center deviates from the laser spot center and the rotation angle increases, the modulated waveform varies from Gaussian to non-Gaussian form, the value of the peak intensity decreases, and the position of the peak intensity shifts. The specific trends of these changes are successfully explained in terms of the geometric characteristics of the target and the spatial intensity distribution of the incident laser. The distinct dependencies of modulated waveforms on geometric shape, size, center position, and rotation angle indicate a convenient method for identity extraction and target recognition in remote sensing using full-waveform LiDAR. This offers exciting implications for applications, such as topological mapping, environment monitoring, and aerial target detection and recognition.

Effects of Nb Addition on Microstructures and Mechanical Properties of Nbx-CoCrFeMnNi High Entropy Alloy Films

In the present work, Nbx-CoCrFeMnNi high entropy alloy films (HEAFs, 0 to 7.2 at.% Nb) were fabricated by radio frequency (RF) magnetron co-sputtering of CoCrFeMnNi alloy and Nb targets. The effects of Nb addition on the microstructures and mechanical properties of HEAFs were systematically investigated. For Nb-free film (0 at.% Nb), the face-centered cubic (FCC) peaks were identified in the X-ray diffraction (XRD) pattern. The addition of Nb resulted in a broadening of diffraction peaks, a decrease in peak intensity, and the vanishment of high-angle peaks. Transmission electron microscope (TEM) images indicated the formation of nanotwins at low Nb concentrations, and a transition from a single phase FCC solid solution to an amorphous phase was observed with the increasing Nb concentration. The films were strengthened with an increase in Nb concentration. Specifically, the hardness characterized by nanoindentation increased from 6.5 to 8.1 GPa. The compressive yield strength and fracture strength measured from micropillar compression tests were improved from 1.08 GPs and 2.56 GPa to 2.70 GPa and 5.76 GPa, respectively, whereas the fracture strain decreased from &gt;29.4% (no fracture) to 15.8%. Additionally, shear banding was observed in the presence of amorphous phase.

Zero-Valent Iron Nanoparticles Induce Reactive Oxygen Species in the Cyanobacterium, Fremyella diplosiphon.

Nanoscale zero-valent iron nanoparticles (nZVIs) are known to boost biomass production and lipid yield in Fremyella diplosiphon, a model biodiesel-producing cyanobacterium. However, the impact of nZVI-induced reactive oxygen species (ROS) in F. diplosiphon has not been evaluated. In the present study, ROS in F. diplosiphon strains (B481-WT and B481-SD) generated in response to nZVI-induced oxidative stress were quantified and the enzymatic response determined. Lipid peroxidation as a measure of oxidative stress revealed significantly higher malondialdehyde content (p < 0.01) in both strains treated with 3.2, 12.8, and 51.2 mg L–1 nZVIs compared to untreated control. In addition, ROS in all nZVI-treated cultures treated with 1.6–25.6 mg L–1 nZVIs was significantly higher than the untreated control as determined by the 2′,7′-dichlorodihydrofluorescein diacetate fluorometric probe. Immunodetection using densitometric analysis of iron superoxide dismutase (SOD) revealed significantly higher SOD levels in both strains treated with nZVIs at 51.2 mg L–1. In addition, we observed significantly higher (p < 0.001) SOD levels in the B481-SD strain treated with 6.4 mg L−1 nZVIs compared to 3.2 mg L–1 nZVIs. Validation using transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDS) revealed adsorption of nZVIs with a strong iron peak in both B481-WT and B481-SD strains. While the EDS spectra showed strong signals for iron at 4 and 12 days after treatment, a significant decrease in peak intensity was observed at 20 days. Future efforts will be aimed at studying transduction mechanisms that cause metabolic and epigenetic alterations in response to nZVIs in F. diplosiphon.

A successful exploitation of gamma-radiation on chalcogenide Cu2InSnS4 towards clean water under photocatalysis approach

The current work represents the inspiration of gamma-radiation on Cu2InSnS4 (CITS) thin films deposited by spray pyrolysis technique. Irradiation treatment was carried out at various absorbed doses (20 – 40- 60 - 80 and 100 kGy) of γ-radiation using as radiation source cobalt-60 (Co-60). The Structural and physical properties of the prepared samples were achieved by means of energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), Maud software, scanning electron microscopy (SEM), spectrophotometer and Drop Shape Analysis System. XRD patterns disclose a decrease in peak intensities followed by the division of peaks related to (204) and (312) lattice strategies after gamma-radiation. All films were crystalized into stannite structure and the crystallites were positioned to (112) plan. Furthermore, EDX spectroscopy reproduces a substantially decrease in Cu, In, Sn and S contents. SEM micrographs obviously display a total morphological modification from nanospherical to pyramidal shapes at 60 kGy, hierarchical rods and lamellar shapes at 100 kGy. In addition, a special emphasis has been focused on surface wettability of irradiated films, which points out the hydrophilic surface after irradiation. As known, hydrophilic character has a distinguished advantageous role on photocatalytic activity that may be due to the active surface area and the adsorption of dye. Based on the relationship between hydrophilicity and photocatalysis, it has been experimentally confirmed the better capacity of irradiated CITS thin film with 60 kGy to decompose Rhodamine B (RhB) dye under Xenon irradiation. Long-term runs approve the stability of irradiated CITS with 60 kGy for photocatalytic process after an overall duration for 5h:30 (4 cycles of 120 min each). This result reveals that irradiated CITS with 60 kGy may be deliberated as an effectual sTable photocatalyst for the remediation of polluted water.

XRD and EDX Analyses on the Formation of MgTiO3 Phase in (Mg0.6Zn0.4)(Ti0.99Sn0.01)O3 Powders Due to Calcination Temperature Variations

MgTiO3-based dielectric ceramics have been recognized as functional materials in the microwave telecommunications industry. Research and development on MgTiO3 dielectric ceramics has therefore developed rapidly. This paper reports x-ray diffraction (XRD) and energy dispersive x-ray (EDX) analyses on the formation of MgTiO3 phase in (Mg0.6Zn0.4)(Ti0.99Sn0.01)O3 powder due to variations in calcination temperature from 550 to 700°C for 2 h. The powder was synthesized via the dissolved metal mixing course using magnesium, zinc, titanium and tin metal powders (Merck) as starting materials. The Rietveld refinement on the XRD patterns of the samples revealed that increasing the calcination temperature reduces the molar% content of MgTiO3 phase of from (97.91±1.51) at 550°C to (87.81±1.29) at 700 °C and causes a decrease in the diffraction peak intensity. The remaining % belongs to TiO2 rutile. The calcination temperature also enlarged the size of MgTiO3 unit cell volume. The EDX data on the atomic% ratio of the elements confirmed the presence of the phases. Discussion of these results is presented in detail in this paper.

Facile, clean and rapid exfoliation of boron-nitride using a non-thermal plasma process

Non-Thermal Plasma source was used in this work to exfoliated boron-nitride (BN) powders. The generation of hexagonal BN nanosheets (h-BNNSs) few-layered was observed by TEM. The hBN exfoliation occurred along their transverse axis, preserving the hexagonal structure. The micrographs showed ordered lattice fringes with d-spacing of approximately 0.33 nm indicating the increase of (0 0 2) h-BNNSs crystal lattice planes, also confirmed by the relative peak intensity decrease in relation to the other peaks in XRD measures. The few amounts of layers were confirmed by intensity decrease, enlargement, and blue shift of E2 g vibrational mode in Raman spectra. Moreover, the appearance of the FTIR band corresponding to the hydroxyl group occurs due to large amounts of defects such as vacancy defects.

LIBS Monitoring and Analysis of Laser-Based Layered Controlled Paint Removal from Aircraft Skin

Reliability and controllability of selective removal of multiple paint layers from the surface of aircraft skin depend on effective online monitoring technology. An analysis was performed on the multi-pulse laser-induced breakdown spectroscopy (LIBS) on the surface of the aluminum alloy substrate, primer, and topcoat. Based on that, an exploration was conducted on the changes of the characteristic peaks corresponding to the characteristic elements that are contained in the topcoat, primer, and substrate with different layers of a laser action, in combination with analysis of microscopic morphology, composition, and depth of laser multi-pulse pits. The results show that the appearance and increase of the characteristic peak intensity of the Ca I at the wavelength of 422.7 nm can be regarded as the basis for the complete removal of the topcoat; the decrease or disappearance of the characteristic peak intensity can be regarded as the basis for the complete removal of the primer. Al I spectrum at the wavelength of 394.5 nm and 396.2 nm can be adopted to characterize the degree of damage to the aluminum alloy substrate. The feasibility and accuracy of the LIBS technology for the laser selective paint removal process and effect monitoring of aircraft skin were verified. Demonstrating that under the premise of not damaging the substrate, laser-based layered controlled paint removal (LLCPR) from aircraft skin can be achieved by monitoring the spectrum and composition change law of specified wavelength position corresponding tothe characteristic elements that are contained in the specific paint layer.

Monitoring the weight and dimensional expansion of pyridostigmine bromide tablets under dynamic vapor sorption and impact of deliquescence on tablet strength and drug release

Changes of weight and axial expansion of tablets of the deliquescent drug pyridostigmine bromide with Kollidon SR were followed with relative humidity (RH) using dynamic vapor sorption and displacement transducer. The effects of RH on placebo and drug containing (API) tablets prepared at low and high compression were related to tablet strength and molecular changes. Tablet weight and expansion increased with RH, especially above RH 40%. Tablet rigidity and strength decreased linearly with moisture for placebo tablets whereas for API tablets there was decrease up to 50% followed by large drop at 60%. Raman spectra of tablets did not show chemical interactions due to moisture, but decreased intensity of drug peak at 2370 cm−1 indicating solid state changes. Decrease of polymer peak intensities at 805 and 1740 cm−1 occurred only in API tablets implicating drug deliquescence in polymer moisture sorption. X-ray diffraction and thermal analysis of tablets indicated complete drug liquefaction after exposure at 60% RH, which impacted great loss of strength but did not affect the sustained release profile. In conclusion, monitoring of the physical properties of tablets during production of deliquescent drugs is necessary to avoid pitfalls during downstream processes such as coating, packaging and storage.

Sulfur speciation in a tropical soil amended with lime and phosphogypsum under long-term no-tillage system

Sulfur (S) is present mainly in organic forms in the most superficial layers of well-drained soils, despite sulfate (SO42−) being the main S-species absorbed by plants. Coupled broadcast application of lime and phosphogypsum (PG) is widely deployed as an agricultural practice to improve soil chemical properties and increase crop yields in highly weathered tropical soil areas under no-tillage system (NTS). However, the effects of large-scale application of these soil amendments to S-species distribution in soil in NTS are largely unknown. We combined S wet-chemical analysis with Synchrotron-based X-ray Absorption Near-Edge Structure Spectroscopy (XANES) to evaluate the effects of lime and PG application to S-species distribution along the soil profile (up to 150 cm). Soil samples were collected from a field-scale experiment under NTS for over 15 years. Soil was amended with lime and PG, either individually or in combination, four times during the experiment. Soil sampling was conducted 16 months after the last amendments’ application, and treatments (lime, PG and lime + PG) were compared to a control (under NTS without amendments’ application) and with soil samples from a native forest (reference for an undisturbed site). Broadcast PG application increased the contents of Ca-phosphate extractable S and pseudo-total S (microwave assisted acid digestion) contents in the deeper layers. Two peaks representing reduced and oxidized S species were detected in S K-edge XANES spectra of all treatments and NF soil. The oxidized S peak gets sharper with increase in depth, as reduced S peak intensity decreases, and fingerprint analysis suggested a greater contribution of reduced organic S species in the most superficial soil layer followed by an increase in highly oxidized S species as depth increased. Linear combination fitting analysis confirmed a greater contribution of highly oxidized S species to the total S-species as depth increased, especially in soil samples that received PG application.

Photoluminescence and energy transfer studies in Ce3+-Sm3+ co-doped phosphate glasses

0.5Ce3+-xSm3+ (x = 0.11, 0.68 and 1.05 mol%) co-doped phosphate glasses were successfully synthesized via melt-quenching method and analyzed using absorption, photoluminescence and decay curves. According to Judd-Ofelt formalism, the Ω2, Ω4 and Ω6 parameters were determined and used to obtain some radiative properties. With the increasing of Sm3+ concentration, it was noticed the decrease of emission peak intensity and decay curves of Ce3+ due to the energy transfer Ce3+→ Sm3+. Moreover, it was observed that the intensity of Sm3+ emission increases until 0.68 mol%, then decreases for the 1.05 mol% Sm3+ concentration. According to the decay curves of Sm3+, this decreasing can be explained by the cross relaxation between Sm3+ ions. The calculated lifetimes by Judd-Ofelt theory and the experimental lifetimes for the prepared phosphate glasses were obtained. The dependence of the emission intensity on the concentration of doping ions has been explained using energy transfer models in order to obtain the optimum Sm3+ concentration.

Exploring Curious Covalent Bonding: Raman Identification and Thermodynamics of Perpendicular and Parallel Pancake Bonding (Pimers) of Ethyl Viologen Radical Cation Dimers.

Viologen radical cations can dimerize in solutions, and the resulting "pimers" were predicted to assemble into parallel and perpendicular conformers by density functional theory (DFT) calculations. Using resonance Raman, we could identify both perpendicular and parallel forms of ethyl viologen dimers. The distinction between the two forms was accomplished by studying the formation of a host-guest complex with γ-cyclodextrin. The dimer's perpendicular form was excluded due to the host cavity size, and γ-cyclodextrin addition caused a decrease in peak intensities at 1171, 1511, and 1602 cm-1 that could be assigned to the perpendicular form. DFT modeling of the vibrational spectra under preresonance conditions allowed us to assign the remaining vibrational modes for the parallel and perpendicular forms. Using variable-temperature UV-vis, the bond dissociation energy (ΔH) for this pancake-bonded dimer was measured as 13.1 ± 0.2 kcal/mol. This type of covalent pancake bonding is a challenge to properly describe using DFT methods. Previously, B97D was found to best describe the ΔG of this dimerization (Angew. Chem. 2017, 129, 9563-9567), but this method underestimates the ΔH by 6 kcal/mol. Of the 11 functionals tested, we found that B3LYP with Grimme's D3 dispersion effect can best reproduce the ΔH. Energy decomposition analysis of the bonding energy showed that solvation effects were the most important contributor-polar solvents are needed to overcome the Coulomb repulsion between the two positively charged monomers. Dispersion effects are second in importance and appear larger than the favorable orbital interaction obtained by singly occupied molecular orbital (SOMO)-SOMO orbital overlap. This study brings forth important insights into the curious cases of covalent bonding between two π-delocalized radicals.