Nitrile IR intensities characterize electric fields and hydrogen bonding in protic, aprotic, and protein environments

Nitriles are widely used as vibrational probes; however, the interpretation of their IR frequencies is complicated by hydrogen bonding (H-bonding) in protic environments. We report a new vibrational Stark effect (VSE) that correlates the electric field projected on the nitrile bond to the transition dipole moment and, by extension, the nitrile peak area or integrated intensity. This linear VSE applies to both H-bonding and non-H-bonding interactions. It can therefore be generally applied to determine electric fields in all environments. Additionally, it allows for semi-empirical extraction of the H-bonding contribution to the blueshift of the nitrile frequency. Nitriles were incorporated at H-bonding and non-H-bonding protein sites using amber suppression, and each nitrile variant was structurally characterized at high resolution. We exploited the combined information now available from variations in frequency and integrated intensity and demonstrate that nitriles are a generally useful probe for electric fields.

Self-referenced method for the Judd–Ofelt parametrisation of the Eu3+ excitation spectrum

Judd–Ofelt theory is a cornerstone of lanthanides’ spectroscopy given that it describes 4fn emissions and absorptions of lanthanide ions using only three intensity parameters. A self-referenced technique for computing Judd–Ofelt intensity parameters from the excitation spectra of Eu3+-activated luminescent materials is presented in this study along with an explanation of the parametrisation procedure and free user-friendly web application. It uses the integrated intensities of the 7F0 → 5D2, 7F0 → 5D4, and 7F0 → 5L6 transitions in the excitation spectrum for estimation and the integrated intensity of the 7F0 → 5D1 magnetic dipole transition for calibration. This approach facilitates an effortless derivation of the Ω6 intensity parameter, which is challenging to compute precisely by Krupke’s parametrisation of the emission spectrum and, therefore, often omitted in published research papers. Compared to the parametrisation of absorption spectra, the described method is more accurate, can be applied to any material form, and requires a single excitation spectrum.

Об экспериментальном определении параметров интенсивности 4f-4f-переходов по спектрам излучения соединений европия (III)

Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning devices. A unique feature of the Eu3+ ion is the experimental determination of the 4f-4f intensity parameters Ωλ directly from the emission spectrum. The equations for determining Ωλ from the emission spectra are different for the detection of emitted power compared to modern equipment that detects photons per second. It is shown that the differences between Ωλ determined by misusing the equations are sizable for Ω4 (ca. 15.5%) for several Eu3+β-diketonate complexes and leads to differences of ca. 5% in the intrinsic quantum yields Q_Ln^Ln. Due to the unique features of trivalent lanthanide ions, such as the shielding of 4f-electrons, which lead to small covalency and crystal field effects, a linear correlation was observed between Ωλ obtained using the emitted power and photon counting equations. We stress that care should be exercised with the type of detection should be taken and provide the correction factors for the intensity parameters. In addition, we suggest that the integrated intensity (proportional to the areas of the emission band) and the centroid (or barycenter) of the transition for obtaining Ωλ should be determined in the properly Jacobian-transformed spectrum in wavenumbers (or energy). Due to the small widths of the emission bands of typical 4f-4f transitions, the areas and centroids of the bands do not depend on the transformation within the experimental uncertainties. These assessments are relevant because they validate previously determined Ωλ without the proper spectral transformation.

Идентификация NV-центров в синтетических флуоресцентных наноалмазах и контроль дефектности кристаллитов методом электронного парамагнитного резонанса

A 100 nm synthetic diamond particle with a large (> 4 ppm) amount of nitrogen vacancy (NV) centers has been studied. The latter exhibit lines associated with forbidden Delta m_s = 2 and allowed Delta m_s = 1 transitions in the electron paramagnetic resonance (EPR) spectra of the ground state of the NV(-) center. The luminescence intensity of particles in the range 550-800 nm increases with an increase in the irradiation dose of 5 MeV electrons and correlates with the integrated intensity of the EPR line with a g-factor g = 4.27.This value is used to estimate the concentration of NV(-) centers and to select diamond powders with the highest fluorescence intensity. The dependence of the EPR signal intensity of the Delta m_s = 2 transition of the NV(-) center on the microwave power has the form of a curve with saturation and subsequent decay, and rather well characterizes the crystal quality of the local environment of the centers under study in these particles. The intensity of the x,y Delta m_s = 1 transition (at ~281.2 mT, 9.444 GHz) turns out to be more sensitive to changes in particle size in the submicron range and the appearance of near-surface defects obtained during mechanical processing.

Exogenous Salicylic and Ascorbic Acids Delay Peel Enzymatic Browning and Improve Quality of Dried Figs Under Low-Temperature Storage

Dried figs undergo undesirable changes during storage, particularly browning reactions. An approach to this issue is using, separately, antioxidants such as ascorbic acid and salicylic acid as anti-enzymatic browning agents. The aforementioned chemical agents were tested at the concentrations 0.1, 0.2, and 0.3% during 6 weeks-storage at 4 °C, for dried figs sealed within polyethylene terephthalate bags. For both agents, the results demonstrated that a concentration of 0.3% lowered the browning index compared to the control by 55 and 54%, respectively. Compared to other concentrations, the same concentration suppressed polyphenol oxidase to 75 and 80%, respectively. A significant impact (p < 0.05), for both treatments, particularly at 0.3%, was obtained on dried figs quality by lowering the total phenols loss and antioxidant capacity loss during the storage period. The results of vibrational spectroscopy were able to confirm the same pattern of the polyphenols compared to those examined by UV-Visible spectrophotometry, revealing thus a decreasing absorbance. A similar tendency was revealed using integrated intensity around the phenols vibration within the region of 1175–940 cm-1, as the concentrations of anti-browning agents increased. Thus, pre-storage ascorbic and salicylic acids treatments at 0.3% on dried figs could be appropriate to delay enzymatic browning and quality loss and, therefore to extend their shelf-life.

A Morphological Classification of 18,190 Molecular Clouds Identified in 12CO Data from the MWISP Survey

We attempt to visually classify the morphologies of 18,190 molecular clouds, which are identified in the 12CO(1–0) spectral line data over ∼450 deg2 of the second Galactic quadrant from the Milky Way Imaging Scroll Painting project. Using the velocity-integrated intensity maps of the 12CO(1–0) emission, molecular clouds are first divided into unresolved and resolved ones. The resolved clouds are further classified as nonfilaments or filaments. Among the 18,190 molecular clouds, ∼25% are unresolved, ∼64% are nonfilaments, and ∼11% are filaments. In the terms of the integrated flux of 12CO(1–0) spectra of all 18,190 molecular clouds, ∼90% are from filaments, ∼9% are from nonfilaments, and the remaining ∼1% are from unresolved sources. Although nonfilaments are dominant in the number of the discrete molecular clouds, filaments are the main contributor of 12CO emission flux. We also present the number distributions of the physical parameters of the molecular clouds in our catalog, including their angular sizes, velocity spans, peak intensities of 12CO(1–0) emission, and 12CO(1–0) total fluxes. We find that there is a systematic difference between the angular sizes of the nonfilaments and filaments, with the filaments tending to have larger angular scales. The H2 column densities of them are not significantly different. We also discuss the observational effects, such as those induced by the finite spatial resolution, beam dilution, and line-of-sight projection, on the morphological classification of molecular clouds in our sample.

In Search of Infall Motion in Molecular Clumps. III. HCO+ (1-0) and H13CO+ (1-0) Mapping Observations toward Confirmed Infall Sources

The study of infall motion helps us to understand the initial stages of star formation. In this paper, we use the IRAM 30 m telescope to make mapping observations of 24 infall sources confirmed in previous work. The lines we use to track gas infall motions are HCO+ (1-0) and H13CO+ (1-0). All 24 sources show HCO+ emissions, while 18 sources show H13CO+ emissions. The HCO+ integrated intensity maps of 17 sources show clear clumpy structures; for the H13CO+ line, 15 sources show clumpy structures. We estimated the column density of HCO+ and H13CO+ using the RADEX radiation transfer code, and the obtained [HCO+]/[H2] and [H13CO+]/[HCO+] of these sources are about 10−11–10−7 and 10−3–1, respectively. Based on the asymmetry of the line profile of the HCO+, we distinguish these sources: 19 sources show blue asymmetric profiles, and the other sources show red profiles or symmetric peak profiles. For eight sources that have double-peaked blue line profiles and signal-to-noise ratios greater than 10, the RATRAN model is used to fit their HCO+ (1-0) lines, and to estimate their infall parameters. The mean V in of these sources is 0.3–1.3 km s−1, and the M ̇ in is about 10−3–10−4 M ⊙ yr−1, which is consistent with the results of intermediate or massive star formation in previous studies. The V in estimated from the Myers model is 0.1–1.6 km s−1, and the M ̇ in is within 10−3–10−5 M ⊙ yr−1. In addition, some identified infall sources show other star-forming activities, such as outflows and maser emissions. Especially for those sources with a double-peaked blue asymmetric profile, most of them have both infall and outflow evidence.

Comment on “Investigation on Anomalous Thermal Quenching of Mn4+ Luminescence in A2XF6:Mn4+” [ECS J. Solid State Sci. Technol. 10 076007 (2021)]

Adachi (ECS J. Solid State Sci. Technol.,10, 076007(2021)) reported that an anomalous enhancement of integrated intensity of Mn4+ luminescence (IPL) in A2XF6:Mn4+ phosphors with increasing lattice temperature was an intrinsic property of the phosphors due to the increased phonon number that makes it possible to gain the parity and spin-forbidden 2Eg → 4A2g transitions.I argue in this comment that it seems still unconvincing to ascribe the anomalous increase of IPL with temperature as an intrinsic property of Mn4+-doped fluorides. Since theoretical derivations of the formulas expressing temperature dependence of the intensities were based on an unjustified assumption.

Samarium doped alkaline earth halides as red-emitting scintillators and phosphors

<p>This thesis is concerned with the manufacture, spectroscopic characterisation, and radiation detection performance of three rare earth doped alkaline earth halides; these were designed for scintillation or phosphor detection of x-rays and γ-rays. The materials are transparent polycrystals of lanthanum or praseodymium stabilised cubic barium chloride ((La,Pr)₀.₁₂₅Ba₀.₈₇₅Cl₂.₁₂₅), BaCl₂ - SrCl₂ solid solutions, or single crystals of CaF₂. The primary dopant investigated was Sm²⁺ since this has a red emission in all the materials which is well matched to the spectral sensitivity of silicon photodiodes. The cubic structure of the polycrystalline materials is essential for optical transparency, and so the structural stability of the materials has been investigated using x ray diffraction and thermal analysis. For CaF₂ large single crystals were unintentionally produced without following the usual Bridgman-Stockbarger or Czochralski methods. All of the materials showed predominantly Sm²⁺ ions, and only in CaF₂ could evidence of Sm³⁺ ions also be seen. The spectroscopy of the 4f⁵5d¹ → 4f⁶ red emission, including lifetimes, and absorption of Sm²⁺ ions in all these materials is reported; a strong thermal cross over to 4f⁶ → 4f⁶ emission is observed and successfully modelled. A time correlated single photon counted system has been built to measure the scintillation decay time of these materials. The system yields decay times in excellent agreement with the literature values. The performance of the materials as scintillators is limited to varying degrees by the formation of colour centres which slow the electron-hole recombination process after x-irradiation. Ba₀.₃Sr₀.₇Cl₂:Sm was found to be a bright and fast x-ray phosphor. The integrated intensity (per x-ray half thickness of material) of the radioluminescence is ~ 30 % that of the commercial material, the scintillation lifetime is ~ 30 μs (c.f. milliseconds for Gd₂O₂S:Tb³⁺) and the imaging resolution is 6 LP/mm (c.f. 4.2 LP/mm for Gd₂O₂S:Tb³⁺). CaF₂:Sm²⁺ was shown to be a red-emitting scintillator with a decay time of ≤ 1 μs and a light output of 15,000 photons/MeV when cooled by dry ice. The x-ray imaging resolution was high at 8.5 LP/mm. Several of the materials have been tested for performance as neutron detecting phosphors by adding neutron capture elements such as gadolinium or lithium, the strongest emission observed was 6 % the integrated intensity of the standard material ⁶LiI(Eu²⁺).</p>

Samarium doped alkaline earth halides as red-emitting scintillators and phosphors

<p>This thesis is concerned with the manufacture, spectroscopic characterisation, and radiation detection performance of three rare earth doped alkaline earth halides; these were designed for scintillation or phosphor detection of x-rays and γ-rays. The materials are transparent polycrystals of lanthanum or praseodymium stabilised cubic barium chloride ((La,Pr)₀.₁₂₅Ba₀.₈₇₅Cl₂.₁₂₅), BaCl₂ - SrCl₂ solid solutions, or single crystals of CaF₂. The primary dopant investigated was Sm²⁺ since this has a red emission in all the materials which is well matched to the spectral sensitivity of silicon photodiodes. The cubic structure of the polycrystalline materials is essential for optical transparency, and so the structural stability of the materials has been investigated using x ray diffraction and thermal analysis. For CaF₂ large single crystals were unintentionally produced without following the usual Bridgman-Stockbarger or Czochralski methods. All of the materials showed predominantly Sm²⁺ ions, and only in CaF₂ could evidence of Sm³⁺ ions also be seen. The spectroscopy of the 4f⁵5d¹ → 4f⁶ red emission, including lifetimes, and absorption of Sm²⁺ ions in all these materials is reported; a strong thermal cross over to 4f⁶ → 4f⁶ emission is observed and successfully modelled. A time correlated single photon counted system has been built to measure the scintillation decay time of these materials. The system yields decay times in excellent agreement with the literature values. The performance of the materials as scintillators is limited to varying degrees by the formation of colour centres which slow the electron-hole recombination process after x-irradiation. Ba₀.₃Sr₀.₇Cl₂:Sm was found to be a bright and fast x-ray phosphor. The integrated intensity (per x-ray half thickness of material) of the radioluminescence is ~ 30 % that of the commercial material, the scintillation lifetime is ~ 30 μs (c.f. milliseconds for Gd₂O₂S:Tb³⁺) and the imaging resolution is 6 LP/mm (c.f. 4.2 LP/mm for Gd₂O₂S:Tb³⁺). CaF₂:Sm²⁺ was shown to be a red-emitting scintillator with a decay time of ≤ 1 μs and a light output of 15,000 photons/MeV when cooled by dry ice. The x-ray imaging resolution was high at 8.5 LP/mm. Several of the materials have been tested for performance as neutron detecting phosphors by adding neutron capture elements such as gadolinium or lithium, the strongest emission observed was 6 % the integrated intensity of the standard material ⁶LiI(Eu²⁺).</p>