Electron Spin Resonance Intensity Research Articles

High-field pulsed EPR spectroscopy under magic angle spinning.

In this work, we demonstrate the first pulsed electron paramagnetic resonance (EPR) experiments performed under magic angle spinning (MAS) at high magnetic field. Unlike nuclear magnetic resonance (NMR) and dynamic nuclear polarization (DNP), commonly performed at high magnetic fields and under MAS to maximize sensitivity and resolution, EPR is usually measured at low magnetic fields and, with the exception of the Spiess group work in the late 1990s, never under MAS, due to great instrumentational challenges. This hampers the investigation of DNP mechanisms, in which electron spin dynamics play a central role, because no experimental data about the latter under DNP-characteristic conditions are available. We hereby present our dedicated, homebuilt MAS-EPR probehead and show the pulsed MAS-EPR spectra of P1 center diamond defect recorded at 7 tesla. Our results reveal unique effects of MAS on EPR line shape, intensity, and signal dephasing. Time-domain simulations reproduce the observed changes in the line shapes and the trends in the signal intensity.

Impact of microwave power on equivalent dose (De) evaluation in ESR dating

ESR (electron spin resonance) spectra of quartz samples irradiated with varying gamma (γ) dose were measured at different microwave power levels (0–200 mW). The microwave power saturation characteristics of Al and E′ centers were systematically investigated, and the mechanisms by which the power saturation characteristics affected equivalent dose (De) fitting results in ESR dating were revealed. The experimental results demonstrated that irradiation reduces the spin-lattice relaxation time, resulting in the inability to intrinsically characterize the number of spins in a series of aliquots when the ESR intensity exhibits significant saturation. The simulation results indicated that changes in spin-lattice relaxation characteristics can cause distortion in the dose response curve (DRC) at high power levels, leading to deviations in De values. A method that uses the slope of the approximate linear regime of the power saturation curve (PSC) as an intrinsic metric of ESR intensity is proposed; this method has been preliminarily validated in both experiments and simulations.

Distribution of Radiation-Induced Defects in Quartz at the ACKIO Uranium Prospect, Athabasca Basin, Saskatchewan: Tracing Uranium-Bearing Fluids

Abstract Quartz grains from the ACKIO uranium prospect, located near the eastern margin of the Athabasca Basin, Saskatchewan, have been investigated using powder X-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of quartz separates from samples systematically collected from the Athabasca Supergroup sandstones and the underlying metamorphosed basement reveal a suite of silicon-vacancy hole centers, which were formed by the bombardment of alpha particles emitted from the radioactive decay of uranium, thorium, and their unstable progeny. The differences in EPR signal intensities of these hole centers indicate that quartz grains received different accumulative doses of alpha particle irradiation in different locations within the ACKIO prospect. For example, quartz extracted from a mineralized sample has the highest EPR signal intensity due to the presence of disseminated uraninite. For quartz sampled at distance from uranium mineralization, the elevated intensities of the silicon-vacancy hole centers most likely indicate a temporary source of radiation, such as ancient uranium-bearing fluids. The median EPR intensities of quartz from the basement rocks at ACKIO are an order of magnitude higher than those of its counterpart from the Athabasca sandstones. Also, the EPR intensities of quartz along the sandstone–basement contact at ACKIO differ by more than two orders of magnitude, suggesting limited migration of uranium-bearing fluids along this contact in the study area. Instead, anomalously high EPR intensities in quartz close to the sandstone–basement contact and elsewhere are restricted to fault gouges and brecciated areas, suggesting that they are the structural pathways for channelized migration of ancient uranium-bearing fluids. A three-dimensional distribution model of the EPR signal intensities has been constructed to define conduits for the migration of ancient uranium-bearing fluids at ACKIO and suggest favorable targets for further exploration. These findings demonstrate the power of EPR spectroscopy in delineating pathways of uranium-bearing fluids and predicting potential mineralization targets.

Investigations on single and multi-grain optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals in quartz derived from sandstones: Insights on provenance of quartz in ancient depositional systems

Trapped charge techniques of luminescence and electron spin resonance (ESR) are classic tools for dating Quaternary deposits. Over the past decade, these techniques have been routinely applied to investigate provenance and/or the sedimentary history of quartz grains based on their different luminescence and ESR characteristics. Of these, optically stimulated luminescence (OSL) sensitivity is one of the most widely investigated parameter for luminescence-based provenance approach. A majority of studies on this parameter are based on evaluation of multi-grain quartz OSL sensitivity of the samples. This is particularly concerning because single-grain quartz luminescence studies have shown that the luminescence signal of a multi-grain aliquot is contributed by less than ∼1–10% of the total grains. Since the sole criteria for discrimination of sources based on luminescence sensitivity relies on its intensity, therefore the results based on multi-grain analysis will most likely be skewed depending on the ‘proportion’ and ‘brightness’ of a few grains. This demands a need to evaluate the potential of single-grain quartz OSL sensitivity in provenance studies. In this study, we investigate single and multi-grain quartz OSL sensitivity from compositionally different sandstones with well-characterised sources based on U–Pb zircon ages. We further complement this analysis with characterisation of ESR centres commonly used in quartz provenance, namely E′1 and [AlO4]0 centres. Our study shows that single-grain quartz OSL sensitivity can help distinguish between sediments that have a predominant input from a single source as compared to those with contribution from multiple sources, which otherwise cannot be inferred from multi-grain studies. Moreover, our results on characterisation of quartz-based ESR intensity of E′1 and saturated [AlO4]0 centres successfully differentiates between sandstones and further complements the luminescence-based characterisation.

Electron Paramagnetic Resonance (EPR) Spectroscopy to Measure Oxidative Stress (OS) in Ulcerative Colitis Mouse

Background: Inflammatory bowel disease (IBD) refers to a group of chronic, complex, relapsing and remitting inflammatory disorders that affect the gastrointestinal (GI) tract. Crohn’s disease (CD) and ulcerative colitis (UC) are the two commonly diagnosed forms of IBD that affect over 3 million Americans, or 1.3% of the US population. In CD, patchy inflammation penetrating through multiple epithelial layers is present in any part of the GI tract, whereas UC is characterized by uniform inflammation restricted to the colon and rectum. Studies have shown increased oxidative stress (OS) as one of the major mechanisms involved in the pathogenesis of UC. Increased OS has thus far been measured using Biochemical assay-kits. In recent studies, electron paramagnetic resonance (EPR) spectroscopy has been extensively used to quantitatively characterize OS level in various tissues. Hypothesis: We hypothesize that EPR technique could be used to characterize OS in epithelia of colon. Aim: We aimed to develop EPR spectroscopy technique to quantify the level of OS in epithelia of normal and UC mouse colon. Methods: Normal mice (C57BL/6 male; 6 – 7 weeks old; Charles River, Wilmington, MA) were given regular water, while acute UC mice were given 5% Dextran-Sulfate-Sodium (DSS) water ad libitum for 7-days. EPR spectroscopy measurements were performed using the redox sensitive hydroxylamine spin probe, 1-hydroxy-3-carboxymethyl-2,2,5,5-tetramethyl-pyrrolidine (CMH; EPR silent). CMH is oxidized by reactive species/oxidants to 3-carboxymethyl-2,2,5,5- tetramethyl-pyrrolidinyloxy radical (CM•; EPR active). We used EPR detected CM• level as a quantitative marker of OS level. OS levels were measured both in serum and distal colon collected from euthanized mice. OS levels were presented as arbitrary units of EPR intensity. Results: OS levels were increased by 41% in serum from UC mice (normal vs UC: 33.6 ± 2.2 vs 47.0 ± 2.0 units; p < 0.011). OS levels were also significantly (60%) increased in UC mice colon compared to normal colon (normal vs UC: 3.5 ± 0.1 vs 5.6 ± 0.7 EPR units; p < 0.02). OS levels were approximately 9-fold higher in serum compared to colon in both normal and UC mice (normal: 3.5 ± 0.1 vs 33.6 ± 2.2; UC: 5.6 ± 0.7 vs 47.0 ± 2.0 EPR signals). Conclusions: We conclude that: 1) EPR spectroscopy technique could successfully be used for the precise measurement of OS levels in serum and colon; 2) OS levels were significantly increased in both serum and colon of UC mice; and 3) increased tissue oxidants were continuously released into the blood. Speculation: Increased serum oxidants may eventually affect other tissues in the body. This study was supported by the West Virginia Clinical and Translational Science Institute (WVCTSI) pilot grant (JTK), and Transition Grant Support, Offce of Research and Graduate Education, WVU Health Sciences Center (VMR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Identifying the plateau sodium storage behavior of hard carbon through the spin state

Hard carbon has emerged as a promising anode material for rechargeable sodium-ion batteries, owing to its abundant precursor sources and remarkable reversible charge storage capacity. The key to achieving an extended sodium storage capacity lies in the plateau capacity largely associated with the closed-pore structure, yet a comprehensive understanding in this area remains incomplete. In our study, we utilized electron paramagnetic resonance (EPR) spectra to discern the spin state of unpaired electrons within hard carbon materials, enabling the identification of sodium storage plateau regions. Hard carbon anodes with plateau capacity predominantly exhibit delocalized spins, evident in the EPR spectrum by limited spin density and a linewidth exceeding 100 G. These spins originate from the extended aromatic structure within small-sized but curved nano-graphite and the closed-pore walls, which are crucial for plateau capacity. Conversely, hard carbon anodes exclusively possessing slope capacity are characterized by localized spins, presenting a typical narrow and intense Lorentzian EPR signal. These localized spins arise from the edge defects of the nano-graphite structure, serving as favourable sites for sodium adsorption. Our development of a methodology to discern hard carbon plateau capacity behavior based on EPR spectra presents a facile and rapid approach for advancing high-performance hard carbon materials.

Establishment an integrable model for expansion the application of the electron spin resonance in materials science

Electron spin resonance (ESR) is a highly successful and widely employed characterization and imaging technique within the field of materials science. Consequently, it has found frequent application in materials domain. However, a substantial number of experimental ESR results in this field lack theoretical explanations due to the absence of precise ESR models. To quantitatively analyze ESR results in materials science, this study has developed an asymmetric ESR spectrum model and assessed its efficacy using twenty-two experimental datasets. This model is integrable and capable of estimating spin concentration. Furthermore, this research has sought to establish quantitative associations between key material preparation parameters and the double integral of ESR intensity. This model is poised to enhance the widespread utilization of ESR in materials science.

Electron paramagnetic resonance of VN–VGa complex in BGaN

A metastable photoinduced electron paramagnetic resonance (EPR) signal at low temperatures is reported for GaN alloyed with boron (i.e., BxGa1−xN) epitaxial layers grown at temperatures ranging from 840 to 1090° C. An isotropic EPR line with g = 2.004 is observed with an intensity depending on the growth temperature for all the samples with boron content between 0.73% and 2.51%. The temperature dependence of EPR intensities is compared with the results of high-resolution photoinduced transient spectroscopy. This enables a link between particular traps and the EPR signal. The activation energies of these traps are consistent with the theoretical position of the VN–VGa complex. Thermal annihilation of the EPR signal with 30 meV activation energy corresponds to shallow donor ionization. A model explaining the light-induced EPR signal that involves redistribution of electrons between deep and shallow donors, mediated by photoionization to the conduction band, is proposed.

Quantitative analyses of the electron spin resonance behavior using an integrable model

Electron spin resonance (ESR) is a spectroscopic method employed to detect distinct species of materials, for example, organic free radicals, transition metal ions, triplet-state molecules, and some point-defect in materials. However, many experimental ESR results of materials have not been theoretically explained due to the lack of a reliable and accurate ESR model. To quantitatively analyze the ESR behavior, we established an asymmetric ESR spectrum model in this study. The effectiveness of this model was confirmed by the results of twenty experimental validations. Because this ESR spectrum model is integrable, spin concentration in materials can be estimated using this model. Furthermore, the quantitative relationships between chemical composition and the double integral of ESR intensity were investigated in this study. The proposed ESR model may expand the application of ESR.

Electron spin resonance study of mixed Bi[formula omitted]Se[formula omitted] topological insulator–magnetic insulator nanoparticles

We investigated Bi2Se3 topological insulator nanoparticles mixed with room-temperature ferromagnetic insulator nanoparticles by using electron spin resonance (ESR) of the surface conduction electrons in the Bi2Se3 nanoparticles. The ESR intensity and linewidth as a function of the molar ratio of the magnetic insulator could be well understood in terms of the magnetic proximity effect due to the short-range exchange field of the magnetic insulator nanoparticles along with the long-range magnetic dipole field effect and the surface-to-volume ratio effect.

Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis

Singlet oxygen (1O2) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1O2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1O2 trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of 1O2 in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate 1O2-driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D 1O2 detection techniques, and provide insights into the reaction mechanisms in 1O2-dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.

Operando ESR observation in thermally activated delayed fluorescent organic light-emitting diodes

Organic light-emitting diodes (OLEDs) using thermally activated delayed fluorescence (TADF) materials have advantages over OLEDs using conventional fluorescent materials or high-cost phosphorescent materials, including higher efficiency and lower cost. To attain further high device performance, clarifying internal charge states in OLEDs at a microscopic viewpoint is crucial; however, only a few such studies have been performed. Here, we report a microscopic investigation into internal charge states in OLEDs with a TADF material by electron spin resonance (ESR) at a molecular level. We observed operando ESR signals of the OLEDs and identified their origins due to a hole-transport material PEDOT:PSS, gap states at an electron-injection layer, and a host material CBP in the light-emitting layer by performing density functional theory calculation and studying thin films used in the OLEDs. The ESR intensity varied with increasing applied bias before and after the light emission. We find leakage electrons in the OLED at a molecular level, which is suppressed by a further electron-blocking layer MoO3 between the PEDOT:PSS and light-emitting layer, resulting in the enhancement of luminance with a low-voltage drive. Such microscopic information and applying our method to other OLEDs will further improve the OLED performance from the microscopic viewpoint.

Modeling and optical characterization of γ-irradiated Cu2+Doped borate glasses as bandpass optical filters

Novel systems of alkali borate glasses with various CuO concentrations from 0.2 up to 1.5 mol% have been prepared by the conventional melt-quenching technique. Several optical, physical, and structural characteristics of the prepared glasses have been examined before and after incremental γ-irradiation doses. The intensity of the blue color of the glasses is controlled by CuO concentrations, with Cu+/Cu2+ in ionic equilibrium. UV/Vis absorption peaks centered at 740 nm can be correlated to a tetragonal twist of the octahedral structure due to 2B1g-2B2g electronic transition. Photoluminescence (PL) extinction spectra can be attributed to Cu+-Cu+ energy migration after Cu+→ Cu2+ energy transfer. Electron spin resonance (ESR) measurements show sharp signals at magnetic fields ranging from 3344 to 3326 Gauss (g = 2.08–2.09), corresponding to the divalent copper state (Cu2+) in octahedral units. FTIR spectra revealed stable structures towards irradiation. Either an increase in CuO content or irradiation led to greater UV absorption, lower PL intensity, lower bandgap (Eopt), lower density, larger molar volume, and slightly more intense ESR signals. Copper ions can be considered as modifiers since they increase the degree of disorder in the glassy network. UV/NIR band stop, FWHM, and center of peaks confirmed the high efficiency of the prepared Cu-doped glasses as colored optical bandpass filters in the green and near-blue regions for UV/IR light laser protection.

Electron spin resonance on a 2D van der Waals CrBr3 uniaxial ferromagnet

We report on the electron spin resonance (ESR) properties of a van der Waals bulk CrBr3 single crystal. Angular- and temperature-dependent studies are performed in the range of the critical temperature for ferromagnetic order. The angular-dependent data enable the determination of a strong uniaxial magnetic anisotropy constant, K, with the easy axis of magnetization being parallel to the crystallographic c axis. The peak-to-peak ESR linewidth below the Curie temperature shows contributions from the term (3 cos2 θ−1)2, thus suggesting the occurrence of long-wavelength (q → 0) modes of spin fluctuations typical for 2D systems. Finally, we analyze the temperature dependence of the double integrated ESR intensity, resonance field, and linewidth for the direction of the magnetic field parallel and perpendicular to the c easy axis. We determine Weiss's constant and the thermal dependence of K and observe the crossover region from linewidth narrowing to broadening approaching the critical temperature. Finally, we discuss our findings in the view of the potential application of CrBr3 in perpendicular magnetic tunneling junctions.

Effect of UV-Light Irradiation on Charge-Accumulation States in PTzBT Polymer Solar Cells

Ternary polymer solar cells based on a polymer PTzBT have received a lot of attention because their power conversion efficiency (PCE) and thermal stability have been greatly improved by adding a small amount of an oligomer ITIC. However, the charge-accumulation states of the PTzBT ternary polymer solar cells have not yet been completely clarified. Here, we report electron spin resonance (ESR) spectroscopy of the PTzBT ternary polymer solar cells to investigate the charge-accumulation states from a microscopic viewpoint with examining the effect of UV-light irradiation. We observed a slight increase in the ESR intensity of the PTzBT cells and layered film samples under simulated solar irradiation with a UV-cut filter. Multiple signals were observed in the PTzBT cells under solar irradiation when the UV-cut filter was removed. Interestingly, no decrease was observed in the ESR signal of ZnO under solar irradiation with the UV-cut filter, although holes in ZnO in the PTzBT cells are known to decrease under solar irradiation. These findings will contribute to a deep understanding of the material properties of polymer solar cells.

Development of a scanning tunneling microscope for variable temperature electron spin resonance.

Recent advances in improving the spectroscopic energy resolution in scanning tunneling microscopy (STM) have been achieved by integrating electron spin resonance (ESR) with STM. Here, we demonstrate the design and performance of a homebuilt STM capable of ESR at temperatures ranging from 1 to 10K. The STM is incorporated with a homebuilt Joule-Thomson refrigerator and a two-axis vector magnet. Our STM design allows for the deposition of atoms and molecules directly into the cold STM, eliminating the need to extract the sample for deposition. In addition, we adopt two methods to apply radio-frequency (RF) voltages to the tunnel junction: the early design of wiring to the STM tip directly and a more recent idea to use an RF antenna. Direct comparisons of ESR results measured using the two methods and simulations of electric field distribution around the tunnel junction show that, despite their different designs and capacitive coupling to the tunnel junction, there is no discernible difference in the driving and detection of ESR. Furthermore, at a magnetic field of ∼1.6T, we observe ESR signals (near 40GHz) sustained up to 10K, which is the highest temperature for ESR-STM measurement reported to date, to the best of our knowledge. Although the ESR intensity exponentially decreases with increasing temperature, our ESR-STM system with low noise at the tunnel junction allows us to measure weak ESR signals with intensities of a few fA. Our new design of an ESR-STM system, which is operational in a large frequency and temperature range, can broaden the use of ESR spectroscopy in STM and enable the simple modification of existing STM systems, which will hopefully accelerate a generalized use of ESR-STM.

EPR study of intrinsic defects within NaYGeO4 olivine

An intense electron paramagnetic resonance (EPR) spectrum has been unexpectedly observed at room temperature in polycrystalline samples of NaYGeO4 with olivine crystal structure. Signals were registered in a wide range of fields up to 6000 ​G. Along with strongly broadened unresolved resonance lines, the relatively narrow spectral components were found. It is shown that the spectrum profile depends on synthesis conditions and mechanical treatment of samples, all suggesting a partial orientational order of microcrystallites in the powders. The spectra are interpreted under the assumption of strong superhyperfine interaction between the oxygen-deficient centers like [GeO3]3- and the nuclei of Na+ cations. In addition, a sharp anisotropic resonance at g-values exceeding free-electron value is attributed to oxygenic-hole centers. The density functional theory (DFT) calculations are employed for the estimation of the thermodynamic stability of various intrinsic defects.

Experimental Study on the Effects of L(+)-Ascorbic Acid Treatment to the ESR Signals of Human Fingernails

The effects of L(+)-ascorbic acid (AA) (an antioxidant commonly known as vitamin C) on the electron spin resonance (ESR) signals from fingernails were examined in relation to X-ray and UV irradiation. The ESR signal intensity, stability, and sensitivity to radiation were measured under different storage conditions. The experimental results indicated that the behavior of the increase in the ESR intensity of the AA samples varied depending on the storage and location conditions, showing sensitivity to light and signal instability at room temperature. It was found that the AA treatment caused a large increase in the peak-to-peak intensities with continuous signal growth with storage time, which may provide an enhancement to the radiation-dependent signal in fingernails. It was also suggested that the use of AA for pre-treatment could sufficiently remove the disturbing signals induced by heat or UV light exposure, which is expected to improve the reliability of radiation dosimetry using fingernails. Further studies with different antioxidant conditions are needed to better characterize the complex changes of the ESR signals from fingernails.

Thermal stability and closure temperature of barite for electron spin resonance dating

Electron spin resonance (ESR) dating has been applied to barite from hydrothermal vents. Barite in hydrothermal vents cools down rapidly after formation so little attention was paid to the thermal stability of the ESR signal of barite for dating. To discern multiple episodes of fluid flow or to date barite in other geological settings, it is essential to know how the ESR intensity decays with heat, the characteristic decay time and the closure temperature. In this study, we demonstrate that the decay of the ESR intensity of the SO 3 − radical in barite is a second-order reaction. The characteristic decay time for the ESR intensity to drop by half at 100 °C, 200 °C, 300 °C and 500 °C is of the order of magnitude of 10 6 years, 10 years, 10 h and 1 s respectively. The closure temperature of barite is generally between 190 and 340 °C. These results provide essential information on environments where the ESR intensity in barite is stable and conditions under which ESR ages can be erased. • ESR intensity of barite decreases rapidly between 300 and 400 °C. • The thermal decay of ESR intensity in barite is a second-order reaction. • The characteristic decay time is at least 8 Ma at 100 °C and 14 years at 200 °C. • The closure temperature is generally between 190 and 340 °C. • ESR dating of barite can be applied to a variety of geological settings.

The relationship between irradiation sensitivity of quartz Al and Ti centers and baking temperature by volcanic lava flow: Example of Datong volcanic group, China

The investigation of irradiation sensitivity of electron spin resonance (ESR) centers is a significant part of the study of ESR signal characteristics and helps to gain insight into the physical mechanisms of paramagnetic centers. In this study, we have observed and compared the irradiation sensitivity characteristics of ESR centers under high-temperature baking in natural conditions by lava flow. Results show that the irradiation sensitivity of the Al and Ti–Li centers increases with the baking temperature, while the irradiation sensitivity of the Ti–H center increases first (up to ∼500 °C) and then decreases with temperature. Moreover, the ESR intensity of the Ti center is more strongly dependent on the annealing history of the samples than the Al center. In addition, from the results of the heating experiment, after heating above 1000 °C, additional irradiation does not produce new Ti–H signals, which probably indicates that the paleo-temperature of the lava flow in Yujiazhai area did not exceed 1000 °C.