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Enhanced Photoluminescence in Quantum Dots–Porous Polymer Hybrid Films Fabricated by Microcellular Foaming
摘要： The color conversion efficiency of thin polymeric layers embedding quantum dots (QDs) is limited by their negligible light scattering ability and by the insufficient absorption of the excitation photons. In this study, a route is presented to tackle these optical shortcomings by introducing a tailored network of micropores inside these hybrid films. This is achieved by exploiting the microcellular foaming approach which is rapid, cost effective and only makes use of a green solvent (supercritical carbon dioxide). With an appropriate combination of the applied pressure and temperature during foaming, and by using a proper film thickness, the photoluminescence (PL) intensity is enhanced by a factor of up to 6.6 compared to an equivalent but unfoamed hybrid film made of CdSe/ZnS QDs in a polymethyl methacrylate matrix. Spectroscopic measurements and ray tracing simulations reveal how the porous network assists UV/blue light absorption by the QDs and the subsequent outcoupling of the converted light. The approach improves the PL for various QD concentrations and can be easily scaled up and extended to other polymeric matrices as well as light converting materials.
关键词： quantum dots,microcellular foaming,porous polymers,photoluminescence,ray tracing simulations
更新于2025-10-22 19:40:53
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The influence of nitrogen doping on the electronic structure of the valence and conduction band in TiO <sub/>2</sub>
摘要： X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) provide a unique opportunity to probe both the highest occupied and the lowest unoccupied states in matter with bulk sensitivity. In this work, a combination of valence-to-core XES and pre-edge XAS techniques are used to determine changes induced in the electronic structure of titanium dioxide doped with nitrogen atoms. Based on the experimental data it is shown that N-doping leads to incorporation of the p-states on the occupied electronic site. For the conduction band, a decrease in population of the lowest unoccupied d-localized orbitals with respect to the d-delocalized orbitals is observed. As confirmed by theoretical calculations, the N p-states in TiO2 structure are characterized by higher binding energy than the O p-states which gives a smaller value of the band-gap energy for the doped material.
关键词： TiO2 doping,X-ray absorption spectroscopy,electronic structure analysis,X-ray emission spectroscopy
更新于2025-09-23 15:23:52
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Attosecond Pulse Shaping by Multilayer Mirrors
摘要： The emerging research field of attosecond science allows for the temporal investigation of one of the fastest dynamics in nature: electron dynamics in matter. These dynamics are responsible for chemical and biological processes, and the ability to understand and control them opens a new door of fundamental science, with the possibility to influence all lives if medical issues can thereby be addressed. Multilayer optics are key elements in attosecond experiments; they are used to tailor attosecond pulses with well-defined characteristics to facilitate detailed and accurate insight into processes, e.g., photoemission, Auger decay, or (core-) excitons. Based on the investigations and research efforts from the past several years, multilayer mirrors today are routinely used optical elements in attosecond beamlines. As a consequence, the generation of ultrashort pulses, combined with their dispersion control, has proceeded from the femtosecond range in the visible/infrared spectra to the attosecond range, covering the extreme ultraviolet and soft X-ray photon range up to the water window. This article reviews our work on multilayer optics over the past several years, as well as the impact from other research groups, to reflect on the scientific background of their nowadays routine use in attosecond physics.
关键词： attosecond,X-ray,extreme ultraviolet (EUV),soft X-ray,multilayer,mirror
更新于2025-09-23 15:23:52
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Potential of GAGG:Ce scintillation crystals for synchrotron X-Ray micro-imaging
摘要： We examined the use of cerium-doped gadolinium aluminum gallium garnet (GAGG:Ce) as a material for scintillation screens in synchrotron X-ray radiography (SXR). Highlighted for gamma-ray detection, GAGG:Ce is also an attractive material for SXR because of its high X-ray stopping power and the high light yield at around 530 nm. A thin and transparent screen prepared from our grown ingot of GAGG:Ce was compared with commonly used scintillators of CdWO4 and YAG:Ce in terms of image quality under monochromatic X-ray illumination. Micron spatial resolutions were achieved with comparable image quality, suggesting that a single crystal of GAGG:Ce is competent scintillation material for SXR.
关键词： Spatial resolutions,GAGG,X-ray detection,Synchrotron X-ray radiography,Scintillator
更新于2025-09-23 15:23:52
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Raman/XRF/EDX microanalysis of 2nd-century stuccoes from Domus Valeriorum in Rome
摘要： 2nd-century stucco fragments from the roman Domus Valeriorum were analyzed by Raman spectroscopy (Raman), imaging X-ray fluorescence (XRF) and energy dispersive X-ray microanalysis (EDX) in order to identify the pigments and materials thereon. Cinnabar, malachite, hematite, goethite and Egyptian blue were detected by the synergistic use of these techniques whereas calcite, with some traces of gypsum, was detected as materials for the bas-relief figures and the pictorial background. This non-destructive characterization is the first carried out on the Domus Valeriorum finds. The multi-analytical approach highlighted the complementarity and versatility of these techniques, suitable for both laboratory and in-situ analysis, on macroscopic or microscopic fragments without preliminary manipulation.
关键词： Energy dispersive X-ray fluorescence,X-ray fluorescence imaging,Domus Valeriorum,Pigments,Raman spectroscopy
更新于2025-09-23 15:23:52
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Determination of high-temperature radiative properties of porous silica by combined image analysis, infrared spectroscopy and numerical simulation
摘要： The influence of the texture of fused silica glasses ? containing unconnected spherical bubbles ? on their thermal radiative properties was investigated by combining experimental measurements and numerical simulations. Exact numerical replicas of the porous samples were obtained from X-ray microtomography and image analysis showed that their bubble populations include two lognormal distributions of radii. The complex refractive index of the silica matrix was extracted from emittance measurements acquired at 1200 K on two reference silica samples. The comparison between direct measurements of the normal spectral emittance of the porous samples and those generated by applying Monte-Carlo ray tracing, performed on the numerical replicas, validated the use of geometric optics. The OH content of the porous samples was evaluated to be around 210 ppm. Ray tracing simulations carried out on a set of virtual samples having a similar texture proved to be a flexible means to address experimental limits when characterizing semi-transparent materials. The simulations also provided a natural framework to test the ability of the modified two-flux approximation model to predict the thermal radiative response of the porous silica investigated.
关键词： Radiative properties,X-ray microtomography,Porous silica glass,Spectral emittance,Monte-Carlo ray tracing
更新于2025-09-23 15:23:52
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A flat-field soft X-ray spectrometer for X-ray absorption spectroscopy measurement of warm dense matter
摘要： A flat-field soft X-ray spectrograph operating in the spectral range of 250–1240 eV was designed and built for warm dense matter and high-energy density plasma physics. It employs a grazing incidence toroidal mirror as a focusing optic, an aberration-corrected variable line spacing concave grating with 2400 lines/mm as a dispersive element, and a charge coupled device as an X-ray detector. The dispersion and energy resolution are calibrated with a high-power laser-produced plasma and X-ray free electron laser sources. A resolving power over 370 was achieved over the entire spectral range. A super broadband spectrum in the range of 250–1000 eV was measured from the laser-produced bismuth plasma. The signal-to-noise of 130 was obtained with an average of 10 pulses. These results demonstrate the capability of the spectrograph for single laser shot based experiments for warm dense matter and high energy density plasma research.
关键词： soft x-ray spectrometer,laser plasma,warm dense matter,x-ray spectroscopy,high power laser
更新于2025-09-23 15:23:52
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Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach
摘要： The contribution of static and thermal disorder is one of the largest challenges for the accurate determination of the atomic structure from the extended X-ray absorption fine structure (EXAFS). Although there are a number of generally accepted approaches to solve this problem, which are widely used in the EXAFS data analysis, they often provide less accurate results when applied to outer coordination shells around the absorbing atom. In this case, the advanced techniques based on the molecular dynamics and reverse Monte Carlo simulations are known to be more appropriate: their strengths and weaknesses are reviewed here.
关键词： Reverse Monte Carlo,Extended X-ray absorption fine structure (EXAFS),Molecular dynamics,Static and thermal disorder,X-ray absorption spectroscopy
更新于2025-09-23 15:23:52
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Short-Period Multilayer X-ray Mirrors for “Water” and “Carbon Windows” Wavelengths
摘要： This review paper summarizes and provides an overview of our recent studies related to two types of short-period multilayer X-ray mirrors, W/B4C and Co/C. It deals with the experimental observation of the layer intermixing effects and how they affect the X-ray mirror's optical performance. The paper presents also some examples of using the fabricated X-ray mirrors in focusing and imaging experiments at the working wavelengths 2.48 nm and 4.47 nm.
关键词： Thin Films,Interlayer Interaction,Metal-Carbon Compositions,Short-Period Multilayer Structures,X-ray Multilayer Mirrors,X-ray Optics
更新于2025-09-23 15:23:52
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-edge resonant inelastic x-ray scattering
摘要： We report an Fe L-edge resonant inelastic x-ray scattering (RIXS) study of the unusual superconductor β-FeSe. The high-energy resolution of this RIXS experiment (≈55 meV FWHM) made it possible to resolve low-energy excitations of the Fe 3d manifold. These include a broad peak which shows dispersive trends between 100 and 200 meV along the (π, 0) and (π, π) directions of the one-Fe square reciprocal lattice, and which can be attributed to paramagnon excitations. The multiband valence state of FeSe is among the most metallic in which such excitations have been discerned by soft x-ray RIXS.
关键词： RIXS,β-FeSe,Fe L-edge,dispersion,paramagnon,superconductor,resonant inelastic x-ray scattering
更新于2025-09-23 15:23:52