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Fine structure in high resolution 4f7?4f65d excitation and emission spectra of X-ray induced Eu2+ centers in LuPO4:Eu sintered ceramics
摘要： X-ray induced effects in LuPO4:Eu3+ sintered thermoluminescent material were investigated by absorption and photoluminescence measurements between 20-300 K. Evidence for Eu3+→Eu2+ conversion upon exposure to X-rays was obtained as narrow band blue Eu2+ photoluminescence was observed. The low temperature luminescence of Eu2+ ions in X-rayed LuPO4:Eu ceramics showed a unique fine structure with a sharp zero-phonon line at 425.8 nm and well-resolved vibronic structure. Excitation spectra of the Eu2+ luminescence revealed a rich structure in which individual 4f7→ 4f6(7FJ)5d1 zero-phonon lines accompanied by vibronic transitions were identified. A detailed analysis allowed an accurate calculation of the Eu3+-like 4f6(7FJ) core levels in the 4f65d1 excited configuration. The 4f6 core splitting is different from that of the 7FJ states for Eu3+ in LuPO4, providing evidence for the role of 4f6-5d interaction on the splitting of the 4f6 configuration. The unique luminescence of Eu2+ with a small Stokes shift and well-determined energies of 4f6(7FJ)5d1 excited states make LuPO4:Eu a model system for testing theoretical models which are presently developed to calculate and predict the energy level structure and Stokes shift of 4fn-4fn-15d1 transitions of lanthanides.
关键词： Eu2+ luminescence,LuPO4,zero-phonon line,high resolution spectroscopy,4f65d excited state
更新于2025-09-09 09:28:46
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Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics
摘要： Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The signi?cant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy.
关键词： terahertz,phonon polariton,ferroelectrics,spectroscopy
更新于2025-09-09 09:28:46
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Binary Zone Plate Infrared Spectrometer for Dissolved Gas Analysis in High Voltage Equipment
摘要： An IR spectrometer based on a Binary Zone Plate (BZP) is presented for dissolved gas analysis. The wavelength selective focal length of the BZP can effectively discriminate between wavelengths ranging from 800 nm to 8 μm, by adjusting the focus distance onto an aperture in the image plane from 19 mm to 200 mm. The aperture serves to pass focused radiation onto the detector. The BZP has a focal length of 50 mm for a design wavelength of 3 μm, with 400 zones. This design enables discrimination between all key fault gases present in oil impregnated high voltage equipment.
关键词： spectrometer,fourier optics,IR spectroscopy,dissolved gas analysis,binary zone plate,gas detection
更新于2025-09-09 09:28:46
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Fourier Transform Infrared Spectroscopy: Applications in Medicine
摘要： Fourier transform infrared spectroscopy (FTIR) is rapidly gaining ground in modern clinical research. This technique is useful for understanding a wide variety of applications ranging from characterization and quality control of various compounds to biomedicine. Importantly, biological materials like proteins, carbohydrates, lipids and nucleic acids have unique structures so it is possible to obtain spectral fingerprints corresponding to their functional groups. FTIR spectroscopic techniques generate an immediate appeal in the field of biology and medicine because of their fast and non-invasive nature. It allows easy visualization of cellular components based on their intrinsic properties and chemical composition. It provides a potential route to screen diagnostic markers for diseases like cancer. FTIR spectroscopy is also considered as a useful tool for analysis of the chemical composition of human calculi. Analysis of stone samples from recurrent stone formers by FTIR may provide a clue to effective prevention of stone recurrence [1]. Fourier transform infrared (FT-IR) spectroscopy has proven to be a fundamental and valuable technique in biology and medicine due to its high sensitivity to detecting changes in the functional groups belonging to tissue components such as lipids, proteins and nucleic acids [2]. Infrared spectra of human and animal tissues could provide information on the molecular structure of tissues. FT-IR has been extensively applied for the determination of a biochemical metabolite in biological fluids. Diagnosis of various types of malignancies such as lung, breast, skin, cervical and colon cancers is already reported in the literature. The spectra are analysed for changes in levels of molecules such as RNA, DNA, phosphates, and carbohydrates. Variation of the RNA/DNA ratio as measured at 1121/1020 cm-1 generally show higher ratio for malignant tissues compared to their non-malignant counterpart. Changes in the spectra of malignant samples were also observed in the symmetric and asymmetric stretching bands of the phosphodiester backbones of nucleic acids, the CH stretching region, the C-O stretching bands of the C-OH groups of carbohydrates and cellular protein residuals, and the pressure dependence of the CH2 stretching mode [3]. The changes in the FTIR spectra correlate to modification of bases and sugars, and redistribution of the H-bond network. The loss/change in the covalent bonds due to damage in the primary, secondary and tertiary structure of nucleic acids can be observed in the spectra. These changes involved the phosphate and C-O stretching bands, the CH stretch region, and the pressure dependence of the CH2 bending and C=O stretching modes. FTIR micro spectroscopy has also been used as a fast diagnostic technique to identify drugs targeting specific molecular pathways causing chronic myeloid leukaemia. Chemometric data analysis was used to assess drug compounds in ex vivo cancer cells [4]. Substantial progress has been made in incorporating advances in computational methods into the system to increase the sensitivity of the entire setup, making it an objective and sensitive technique suitable for automation to suit the demands of the medical community. FTIR spectroscopy provides the possibility of obtaining information on molecular composition and structure at the level of single cell within a time-scale of few seconds-minutes and to perform qualitative and quantitative multi-component analyses. It helps in automated pattern recognition and objective classifications of samples with minimal and label-free sample treatment. The technical improvements will progressively increase the number of potential applications of micro FT-IR to cancer research and clinical diagnosis. It may be hoped that the future pre-clinical and clinical trials will include sample evaluation utilizing this technique in order to obtain data necessary to validate the use of micro FT-IR spectroscopy in a clinical context. In fact, this appears to be the most important way to reduce the high level of skepticism of many biologists and pathologists about an old technology that has been designed and improved mainly for applications in clinical diagnosis including cancer research.
关键词： cancer research,biomedicine,clinical diagnosis,Fourier transform infrared spectroscopy,FTIR,clinical research
更新于2025-09-09 09:28:46
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Simulating X-ray emission spectroscopy with algebraic diagrammatic construction schemes for the polarization propagator
摘要： The calculation of X-ray emission spectra has been addressed with the algebraic diagrammatic construct (ADC) scheme, using a core-ionized wave function as the reference state. With this, the valence-to-core transitions are found as the first eigenstates with negative eigenvalues. The performance of the ADC hierarchical methods ADC(2), ADC(2)-x, and ADC(3/2) has been investigated on 17 transition of second-row elements (C, N, O, F, and Ne), and 5 transitions of third-row elements (S and Cl). We report ADC(2) results within 0.28±0.35 eV of experimental values with an appropriate choice of basis set and when accounting for relativistic effects, with a slight tendency towards underestimating emission energies. By comparison, ADC(2)-x yields a similar spread in relative energies, but a consistent overestimation of approximately 1.5 eV. Going to ADC(3/2), we now observe an underestimation of emission energies and a larger error spread. By comparison, calculations of X-ray absorption spectra have been reported to favour the ADC(2)-x method, with ADC(2) showing the largest error when comparing to experimental values. The difference in ADC performance trends between these core spectroscopies are attributed to the different electron rearrangement effects in X-ray absorption and emission processes.
关键词： valence-to-core transitions,core-hole,X-ray emission spectroscopy,polarization propagator,algebraic diagrammatic construction
更新于2025-09-09 09:28:46
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Surface Chemistry and Long-Term Stability of Amorphous Zn-Sn-O Thin Films
摘要： Amorphous (a-) oxides form an important category of transparent conducting/semiconducting thin films used as electrodes and channel layers in thin film transistors. The compositional flexibility of amorphous states, through doping, makes it possible to fine tune the electrical properties of films from conducting to semiconducting. However, surface chemistry and stability of these films are rarely addressed. Surface studies of amorphous materials, in general, are scarce due to disorder. Here, long-term surface stability of a-Zn-Sn-O films is investigated using grazing incidence X-ray absorption spectroscopy techniques. We present a detailed description of film surface structures and their evolution over time. It is found that the surface structure is, locally, a close analogue of the crystalline counterpart and that surface chemistry is governed by vacancies, strain, composition, and film density. It will be shown that the long-term stability of a film is questionable when the film has a high Zn content and a low density.
关键词： Zn-Sn-O thin films,Long-term stability,Grazing incidence X-ray absorption spectroscopy,Surface chemistry,Amorphous oxides
更新于2025-09-09 09:28:46
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Conductance Spectroscopy of Exfoliated Thin Flakes of Nb <sub/>x</sub> Bi <sub/>2</sub> Se <sub/>3</sub>
摘要： We study unconventional superconductivity in exfoliated single crystals of a promising 3D topological superconductor candidate, Nb-doped Bi2Se3 through differential conductance spectroscopy and magneto-transport. The strong anisotropy of the critical field along the out-of-plane direction suggests that the thin exfoliated flakes are in the quasi-2D limit. Normal metal-superconductor (NS) contacts with either high or low transparencies made by depositing gold leads onto Nb-doped Bi2Se3 flakes both show significant enhancement in zero bias conductance and coherence dips at the superconducting energy gap. Such behavior is inconsistent with conventional Blonder-Tinkham-Klapwijk theory. Instead, we discuss how our results are consistent with p-wave pairing symmetry, supporting the possibility of topological superconductivity in Nb-doped Bi2Se3. Finally, we observe signatures of multiple superconducting energy gaps, which could originate from multiple Fermi surfaces reported earlier in bulk crystals.
关键词： differential conductance spectroscopy,unconventional superconductivity,topological superconductivity,p-wave pairing symmetry,Nb-doped Bi2Se3
更新于2025-09-09 09:28:46
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Sensitive X-ray Absorption Near Edge Structure Analysis on the Bonding Properties of Au <sub/>30</sub> (SR) <sub/>18</sub> Nanoclusters
摘要： Au nanoclusters (NCs) with organothiolate protecting ligands are a field of great interest and X-ray absorption spectroscopy is a useful tool for the structure and property studies of these Au NCs. However, the Au NCs normally show broad and low-intensity features in the gold X-ray absorption near-edge structure (XANES) region, lowering the sensitivity of the technique and making it difficult to use for the analysis of Au NCs. In this work we report a sensitive gold L3-edge XANES study on the bonding properties of the newly discovered Au30(SR)18 NCs utilizing a combined approach of the first derivative XANES spectra and quantum simulations. First derivative XANES spectra are compared with the well-studied Au25(SR)18 with the aim of determining the unique features of Au30(SR)18. It is found that the early XANES region of the Au NCs is significantly influenced by the gold?gold bonding environment in the surface sites, as the varying surface Au?Au bond lengths in Au25(SR)18 and Au30(SR)18 result in pronounced difference in the first derivative XANES. These findings can be consistently explained using site-selective quantum simulations of the XANES spectra based on the Au NC structural models. The XANES method presented in this work offers a useful tool for the sensitive analysis on structure and bonding properties of Au NCs.
关键词： Au nanoclusters,bonding properties,quantum simulations,XANES,X-ray absorption spectroscopy
更新于2025-09-09 09:28:46
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Real-time parallel 3D multiple particle tracking with single molecule centrifugal force microscopy
摘要： Real-time tracking of multiple particles is key for quantitative analysis of dynamic biophysical processes and materials science via time-lapse microscopy image data, especially for single molecule biophysical techniques, such as magnetic tweezers and centrifugal force microscopy. However, real-time multiple particle tracking with high resolution is limited by the current imaging processes or tracking algorithms. Here, we demonstrate 1 nm resolution in three dimensions in real-time with a graphics-processing unit (GPU) based on a compute unified device architecture (CUDA) parallel computing framework instead of only a central processing unit (CPU). We also explore the trade-offs between processing speed and size of the utilized regions of interest and a maximum speedup of 137 is achieved with the GPU compared with the CPU. Moreover, we utilize this method with our recently self-built centrifugal force microscope (CFM) in experiments that track multiple DNA-tethered particles. Our approach paves the way for high-throughput single molecule techniques with high resolution and efficiency.
关键词： image processing,single molecule force spectroscopy,GPU,particle tracking
更新于2025-09-09 09:28:46
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Ultrafast excited-state dynamics in chlorosomes isolated from the photosynthetic filamentous green bacterium <i>Chloroflexus aurantiacus</i>
摘要： Bacteriochlorophyll (BChl) c pigments in the aggregated state are responsible for efficient light harvesting in chlorosomes of the filamentous anoxygenic photosynthetic bacterium, Chloroflexus (Cfx.) aurantiacus. Absorption of light creates excited states in the BChl c aggregates. After sub-picosecond intrachlorosomal energy transfer, redistribution and relaxation, the excitation is transferred to the BChl a complexes and further to reaction centres on the picosecond time scale. In this work, the femtosecond excited state dynamics within BChl c oligomers of isolated Cfx. aurantiacus chlorosomes was studied by double difference pump-probe spectroscopy at room temperature. Difference (Alight ? Adark) spectra corresponding to excitation at 725 nm (blue side of the BChl c absorption band) were compared with those corresponding to excitation at 750 nm (red side of the BChl c absorption band). A very fast (time constant 70 ± 10 fs) rise kinetic component was found in the stimulated emission upon excitation at 725 nm. This component was absent at 750-nm excitation. These data were explained by the dynamical red shift of the stimulated emission due to excited state relaxation. The nature and mechanisms of the ultrafast excited state dynamics in chlorosomal BChl c aggregates are discussed.
关键词： excited-state dynamics,Chloroflexus aurantiacus,Bacteriochlorophyll,chlorosomes,pump-probe spectroscopy
更新于2025-09-09 09:28:46