X-ray Emission Spectra Research Articles

Luminescence properties of composite material Sr2MgSi2O7:Eu2+,Dy3+/light conversion agent with multilayer structure

In order to improve the red luminescent properties, Sr2MgSi2O7:Eu2+,Dy3+ was selected as a blue persistent luminescent donor phosphor, while light conversion agent was utilized to tune the persistent luminescent spectra from blue to red. Composite red luminescent material Sr2MgSi2O7:Eu2+,Dy3+/light conversion agent (SMED/LCA) was fabricated with light conversion agent and Sr2MgSi2O7:Eu2+,Dy3+ at a certain mass ratio. SiO2 (Al2O3 or MgF2) were coated on the surface of SMED/LCA through heterogeneous deposition method. The structural and optical characteristics of the resulting samples were launched in terms of X-ray diffraction and emission spectrum as well as afterglow brightness. The results demonstrate that the emission spectrum exhibits two emission bands, and the peaks are located at around 470 and 615 nm. SiO2, Al2O3 and MgF2 are coated on the surface of SMED/LCA like a protective shell to maintain its stability and luminescent properties, the afterglow initial brightness is still up to 0.37 cd/m2 and the afterglow color purity calculated from CIE color coordinates is basically unchanged.

X-ray Spectroscopic Studies of a Solid-Density Germanium Plasma Created by a Free Electron Laser

The generation of solid-density plasmas in a controlled manner using an X-ray free electron laser (XFEL) has opened up the possibility of diagnosing the atomic properties of hot, strongly coupled systems in novel ways. Previous work has concentrated on K-shell emission spectroscopy of low Z (<= 14) elements. Here, we extend these studies to the mid-Z(=32) element Germanium, where the XFEL creates copious L-shell holes, and the plasma conditions are interrogated by recording of the associated L-shell X-ray emission spectra. Given the desirability of generating as uniform a plasma as possible, we present here a study of the effects of the FEL photon energy on the temperatures and electron densities created, and their uniformity in the FEL beam propagation direction. We show that good uniformity can be achieved by tuning the photon energy of the XFEL such that it does not overlap significantly with L-shell to M-shell bound-bound transitions, and lies below the L-edges of the ions formed during the heating process. Reasonable agreement between experiment and simulations is found for the emitted X-ray spectra, demonstrating that for these higher Z elements, the selection of appropriate XFEL parameters is important for achieving uniformity in the plasma conditions.

The X-ray emission of cerium oxide

Using a combination of spectral simulation with FEFF and experimental data for metallic Ce, it has been possible to extract the Cerium Oxide-only M4,5 X-ray Emission Spectrum (XES) from an experimental result, which had been produced utilizing a combined CeOxide/Ce sample. It is shown that the XES emission for CeOxide-only is significantly different for the M4 and M5 edges, with the M4 XES consistent with normal XES and the M5 XES exhibiting a continued enhancement associated with a threshold effect, connected to Resonant Inverse Photoelectron Spectroscopy (RIPES).

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 1017 and 1018 W cm-2. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted ‘probe-before-destroy’ measurement strategy can be adopted for electronic-structure related XFEL experiments.

Site-Specific Pressure-Driven Spin-Crossover in Lu1-xScxFeO3.

Pressure-driven spin-crossover (PSCO) is a collective quantum phenomenon frequently observed in transition-metal-based systems. According to the crystal-field theory, PSCO highly depends on the surrounding coordination environment of a given magnetic ion; nevertheless, it has never been verified experimentally up to now. Herein, we report the observation of a site-specific PSCO phenomenon in Lu1-xScxFeO3, in which octahedrally coordinated Fe3+ in orthorhombic LuFeO3 and trigonal-bipyramidally coordinated Fe3+ in hexagonal Lu0.5Sc0.5FeO3 show distinct PSCO response to external pressure. X-ray emission spectra and DFT calculations reveal the key role of coordination environment in a PSCO process and predict the occurrence of PSCO for trigonal-bipyramidally coordinated Fe3+ above 100 GPa, far beyond that of 50 GPa for octahedrally coordinated Fe3+ in LuFeO3. The demonstration of site-specific PSCO sheds light on the state-of-the-art design of PSCO materials for directional applications.

Synthesis, crystal structure and photoluminescence properties of high-color-purity red-emitting SrLu2O4:Eu3+ phosphors with excellent thermal stability

Red-emitting SrLu2O4:Eu3+ phosphors were prepared by a high-temperature solid-state reaction approach, and they were characterized by X-ray diffraction (XRD), excitation and emission spectra, luminescence decay lifetimes, CIE chromaticity coordinates, and temperature-dependent emission spectra. Rietveld refinement of XRD pattern revealed that the SrLu2O4:Eu3+ phosphors crystallized into orthorhombic crystal system with a space group of Pnma and cell parameters of a = 9.962(1) Å, b = 3.343(5) Å, c = 11.746(2) Å, α = β = γ = 90°, and V = 391.24(3) Å3. Under 395 nm excitation, these SrLu2O4:Eu3+ phosphors showed intense red emissions in the 550-750 nm wavelength range with peaks around 581, 593, 611, 653, and 708 nm, corresponding to the 5D0→7FJ (J = 0-4) transitions of Eu3+ ions. Investigation on Eu3+ doping concentration dependent emission spectra demonstrated the critical quenching concentration of Eu3+ ions was 9 mol%. The luminescence decay lifetimes declined from 1.77 to 1.51 ms with increasing Eu3+ concentration from 1 to 10 mol%. Notably, the CIE chromaticity coordinates (0.646, 0.354) of composition-optimal SLO:9%Eu3+ phosphors were close to the standard red light (0.67, 0.33), and its color purity reached as high as 94.1%. Finally, it was found that the SLO:9%Eu3+ phosphors also had excellent thermal stability and color stability at higher temperatures. The emission intensity at 423 K was dropped to 89% of that at 303 K, and the activation energy of thermal quenching was 0.32 eV.

A Study of Low-Temperature Neutron Star Atmospheres

We present a study of how a low-temperature accreted atmosphere influences the emitted X-ray spectrum of a neutron star. The atmosphere models and spectra were computed with Zcode, a multigroup radiation transfer code developed at the Los Alamos National Laboratory. Though the underlying hot neutron star behaves as a blackbody, the atmosphere shifts the peak of spectrum away from a blackbody and toward higher energies, producing an emitted spectrum similar to a dilute blackbody. Quantifying the effects of this atmosphere will remove a source of uncertainty in X-ray observations and better constrain the mass-radius relation for neutron stars and thus the equation of state of dense matter. We present a suite of these atmospheres with varying compositions and temperatures as well as the resulting spectra.

Color tunable luminescence and optical temperature sensing performance in a single-phased KBaGd(WO4)3:Dy3+, Eu3+ phosphor

Abstract Herein, a series of Dy3+, Eu3+ single/co-doped KBaGd(WO4)3 phosphors (KBGW:Dy3+, Eu3+ for short) were prepared by solid-state reaction method and investigated by means of X-ray diffraction, SEM, photoluminescence excitation and emission spectra, decay curves and thermal quenching behavior. The KBGW:xDy3+ phosphors exhibited a weak blue emission around 480 nm and a strong yellow emission around 580 nm, corresponding to the characteristic 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions respectively. The decay curves of the KBGW:xDy3+ phosphors were analyzed in the framework of the Inokuti-Hirayama (IH) model and the concentration quenching mechanisms were determined to be dipole-dipole interactions. Under the excitation of 250 nm and 352 nm, both the characteristic emissions of Eu3+ and Dy3+ ions were observed in the KBGW:Dy3+, Eu3+ phosphors. Furthermore, with the increasing concentration of Eu3+, color-tunable emissions from yellow to red were obtained in these samples. Based on the thermal quenching behavior, the optical sensitivity of the sample to temperatures, including absolute sensitivity (Sa) and relative sensitivity (Sr), were calculated and evaluated for the application in optical thermometry.

The soft excess of the NLS1 galaxy Mrk 359 studied with an XMM-Newton-NuSTAR monitoring campaign

Context. Joint XMM-Newton and NuSTAR multiple exposures allow us to disentangle the different emission components of active galactic nuclei (AGNs) and to study the evolution of their different spectral features. In this work, we present the timing and spectral properties of five simultaneous XMM-NewtonandNuSTAR observations of the Narrow Line Seyfert 1 galaxy Mrk 359. Aims. We aim to provide the first broadband spectral modeling of Mrk 359 describing its emission spectrum from the UV up to the hard X-rays. Methods. We performed temporal and spectral data analysis, characterising the amplitude and spectral changes of the Mrk 359 time series and computing the 2–10 keV normalised excess variance. The spectral broadband modelling assumes the standard hot Comptonising corona and reflection component, while for the soft excess we tested two different models: a warm, optically thick Comptonising corona (the two-corona model) and a reflection model in which the soft-excess is the result of a blurred reflected continuum and line emission (the reflection model). Results. High and low flux states were observed during the campaign. The former state has a softer spectral shape, while the latter shows a harder one. The photon index is in the 1.75–1.89 range, and only a lower limit to the hot-corona electron temperature can be found. A constant reflection component, likely associated with distant matter, is observed. Regarding the soft excess, we found that among the reflection models we tested, the one providing the better fit (reduced χ2 = 1.14) is the high-density one. However, a significantly better fit (reduced χ2 = 1.08) is found by modelling the soft excess with a warm Comptonisation model. Conclusions. The present analysis suggests the two-corona model as the best scenario for the optical-UV to X-ray emission spectrum of Mrk 359.

Laser-induced inner-shell excitations through direct electron re-collision versus indirect collision

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion.

Calculation of reliable non-resonant Kα X-ray emission spectra of organic molecules and other small molecules

For reliable calculation of vertical ionization energies (VIEs) of both core and valence electrons of gas-phase organic molecules and other small molecules, we developed DFT procedures in 1999 and 2009. The difference between core and valence VIEs give the energies for X-ray emission spectra (XES). The dipole matrix elements between core and valence electrons required for calculation of the XES intensities are now easily available. The simple procedure for calculation of reliable XES is demonstrated by comparison with known XES for H2O(g), NH3(g), CO(g), CO2(g), N2(g), and NNO(g). Consequently, the XES of H2CO(g), formamide(g), 1-nitrosamine(g), N-methylformamide(g), 1-nitrosoaziridine(g), and oxirane(g) are predicted with confidence.

A novel blue-purple Ce3+ doped whitlockite phosphor: Synthesis, crystal structure, and photoluminescence properties

At present, the rare earth (RE) ions doped phosphors have attracted more and more attention because of their excellent properties. In this paper, a series of novel blue-purple β-Ca3(PO4)2:Ce3+ phosphors were synthesized by a high temperature solid phase method. The X-ray diffraction (XRD), infrared spectrum, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence excitation and emission spectra were used to investigate the crystal structure, composition and the luminescent properties of the resulting samples. The phosphor shows a strong absorption in the ultraviolet band. Under the excitation of 269 nm, the phosphor emits a strong purple fluorescence ranging from 360 to 520 nm. When Ce3+ doping content is 0.07 mol, the strongest luminescence intensity is reached, and the concentration quenching mechanism is dipole-dipole (d-d) interaction for Ce3+ based on Dexter theory.

Synthesis and photoluminescence characteristics of Dy incorporated MoO3 phosphor: Suppression concentration quenching

A series of MoO3:Dy3+ phosphors have been synthesized via the gel-combustion method. The X-ray and photoluminescence (PL) emission spectra were employed to characterize the obtained phosphors. The prepared samples were characterized through XRD measurements and exhibited that Dy3+ ions can be successfully incorporated into the host material. The PL emission bands of Dy3+ doped MoO3 were observed at 486 nm, 574 nm and 666 nm which are assigned to the transitions of 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2, respectively. Concentration quenching were largely taken into consideration as one of the crucial aspects limiting the application range of phosphors in today's modern world. An abnormal thermal quenching dependence was reported when Dy3+ ions were incorporated into MoO3 host matrix. In order to understand the origin of this beneficial behaviour, energy transfer processes occurring via radiative and nonradiative mechanisms were investigated to elucidate this suppression of the concentration quenching.

Operation of a bending magnet beamline in large energy bandwidth mode for non-resonant X-ray emission spectroscopy

Two new operation modes, “pink beam” excitation, which has the energy bandwidth defined by X-ray mirrors and filters, and “broadband beam”, where the energy bandwidth is defined by the reflection from a multilayer monochromator, were implemented at the SuperXAS beamline of the Swiss Light Source (SLS). These setups allow measuring non-resonance X-ray emission spectra (XES) with 2–3 orders of magnitude higher incident flux than non-resonant XES measurements with a monochromatic incident beam. For the broadband beam mode, a Mo/Si multilayer structure was designed, with which the energy can be tuned in the 5–17 keV range. The multilayer demonstrates a relatively large energy bandwidth of 4 ± 0.2% through the whole energy range and a reflectivity of 23–60%, which increases with energy. We show that by using pink beam mode one can investigate the electronic structure of photocatalytic intermediates through time-resolved core-to-core XES experiments of diluted samples with a concentration of the element of interest of ~1 mM. Broadband beam mode is optimal for valence-to-core XES experiments and allow to avoid the excitation of additional KLβ satellites that can complicate the interpretation of spectra.

Soft X-ray and EUV emission spectra of beryllium plasma produced by neodymium-glass laser radiation with broad frequency and angular spectra

We present the results of an experimental study of soft X-ray (SXR) and extreme ultraviolet emission spectra of the plasma produced by exposing a plane solid beryllium target to laser radiation with broad frequency and angular spectra. SXR lines up to 1s – 9p of Be IV as well as the plasma continuum are recorded for a laser focal-spot intensity of 5.3 × 1013 W cm−2. To model the SXR beryllium plasma spectra, simulations are carried out using the INDHAUS programme and the FLYCHK code in the framework of local thermodynamic equilibrium model, which agree nicely with experimentally obtained results.

Cornell’s Role in Developing Synchrotron Radiation for Mineral Physics

The newly invented diamond anvil cell (DAC) in 1960, and the newly constructed Cornell High Energy Synchrotron Source (CHESS) in 1979 were a perfect match, as CHESS could provide such an intense X-ray beam with such extraordinary properties that a whole new approach to mineral physics research became possible. The very high intensity of the X-ray beam from CHESS made it possible to make real-time observations of crystal structures during phase transitions for the first time. For instance, the olivine-spinel transition, important for understanding deep focus earthquakes can be shown to take place first by the displacive shift of oxygen layers supporting shear stress as most likely earthquake trigger followed by the diffusion of the cations to their positions in the spinel structure. X-ray emission spectra of high-pressure, high-temperature samples also made it possible to determine phase compositions, as well as the structures of complex ions in solution.

Tl₂ZrCl₆ and Tl₂HfCl₆ Intrinsic Scintillators for Gamma Rays and Fast Neutron Detection

Thallium zirconium chloride (Tl2ZrCl6) and its hafnium analog (Tl2HfCl6) are intrinsic scintillators that have been recently reported, primarily for gamma-ray detection and spectroscopy. These crystals are especially useful for dual-mode detection, gammas exploiting the highly effective $Z$ of the materials, and fast neutrons using the (n, p) and (n, $\alpha$ ) reactions with chlorine. $Z_{\mathrm {eff}}$ (70.7) and high photoelectric conversion efficiency of the zirconium variant without any activator makes it particularly attractive in this regard. We report here on the growth of undoped Tl2ZrCl6 and Tl2HfCl6 crystals using vertical Bridgman technique. The X-ray emission spectrum shows a broadband in the range of 400–600 nm with a peak around 470 nm for both crystals. The light yields (LYs) of these crystals were measured under irradiation by a 137Cs gamma source (662 keV) and compared with that from the commercial Tl-doped NaI crystal. Normalized for the quantum efficiency of the photomultiplier (PMT) at the relevant emission wavelengths, the respective LYs of Tl2ZrCl6 and Tl2HfCl6 are estimated to be 40 000 and 18 000 photons/MeV with corresponding energy resolution of 5% and 9%, respectively. We have demonstrated for the first time the neutron detection capability of these materials showing excellent pulse shape discrimination (PSD) with figure of merit on the order of 2.4. PSD measurement of Tl2ZrCl6 using a 241AmBe source demonstrates well-separated gamma, recoiled proton, and alpha particle bands.

Eu3+-activated Ca2YTaO6 double-perovskite compound: A novel highly efficient red-emitting phosphor for near-UV-excited warm w-LEDs

In this work, novel Eu3+ ions activated red emitting Ca2YTaO6 (CYT) phosphors have been prepared via a high-temperature solid-state reaction approach. Their crystal structure and photoluminescence properties were investigated by X-ray diffraction (XRD) patterns, photoluminescence excitation and emission spectra, and decay lifetimes. XRD Rietveld refinement results revealed that the CYT:Eu3+ phosphors crystallized in the monoclinic structure with the space group of P21/n and lattice parameters of a = 5.5989 Å, b = 5.8449 Å, c = 8.1016 Å, α = γ = 90°, β = 89.8799°, and V = 264.625 Å3. The CYT:xEu3+ phosphors could be excited by near-ultraviolet light around 396 nm, and they showed bright narrowband red emissions peaking at 590, 614, 656, and 703 nm due to the 5D0→7FJ (J = 1–4) transitions of Eu3+ ions. The 614 nm red emission corresponding to the 5D0→7F2 transition was dominant in the emission spectra, indicating that the Eu3+ ions occupied non-centrosymmetric sites. The critical quenching concentration in CYT:xEu3+ phosphors was 50 mol%, and the optimal CYT:0.5Eu3+ phosphors showed PL intensity as great as 4.2 times higher than the commercial red phosphors Y2O3:Eu3+. CIE chromaticity coordinates of CYT:0.5Eu3+ phosphors were (0.6678, 0.3319), and the color purity reached up to 97.4%. The nonradiative energy transfer between the Eu3+ ions in the CYT host was attributable to dipole-dipole interaction, and the critical distance was roughly 7.97 Å. A warm white light-emitting diode (w-LED) based on the combination of a 395 nm LED chip with a blend of commercial BaMgAl10O17:Eu2+blue phosphors and commercial (Ba,Sr)2SiO4:Eu2+ green phosphors and as-prepared CYT:0.5Eu3+ red phosphors was fabricated, which gave warm white-light emission with excellent CIE color coordinates of (0.3833, 0.3859), low correlated color temperature of 3991 K, high color rendering index of 92.1, and good luminous efficacy of 21.76 lm/W.

Preparation, crystal structure, and photoluminescence properties of high-brightness red-emitting Ca2LuNbO6:Eu3+ double-perovskite phosphors for high-CRI warm-white LEDs

Near-ultraviolet-excited efficient red phosphors are important for fabricating warm-white light-emitting diodes (LEDs) with high color rendering index. Herein, we demonstrated the preparation of novel highly efficient Eu3+ ions-activated Ca2LuNbO6 (CLN) double-perovskite phosphors. These phosphors were prepared by the high-temperature solid-state reaction method and they were characterized by powder X-ray diffraction, Rietveld refinement, excitation and emission spectra, decay lifetimes, internal quantum efficiency, and temperature-dependent emission spectra. The as-prepared phosphors can be efficiently excited by 396 nm near-ultraviolet light and generated bright red luminescence around 591, 616, 656 and 703 nm corresponding to the 5D0→7FJ (J = 1–4) transitions of Eu3+ ions. The optimal doping concentration of CLN:xEu3+ (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8) phosphors was x = 0.4, and the optimal CLN:0.4Eu3+ sample exhibited high-color-purity (96.4%) red emission with internal quantum efficiency as great as 66%. The thermal-quenching resistance was evaluated by measuring their temperature-dependent emission intensities, while the emission intensity at 150 °C was about 65% of that at room temperature. Finally, a warm white LED lamp was made by using a 395 nm LED chip together with a phosphor blend of commercial blue phosphor BaMgAl10O17:Eu2+ and commercial green phosphor (Ba,Sr)2SiO4:Eu2+ and newly developed red phosphor CLN:0.4Eu3+, which gave bright high-quality white light with Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of (0.3878, 0.3725), a correlated color temperature of 3769 K, and a color rendering index of 94 when the driven current was 20 mA. These investigation results clearly revealed the promising application potential of CLN:Eu3+ red phosphors in high-color-quality solid-state white lighting.

A NICER View of Spectral and Profile Evolution for Three X-Ray-emitting Millisecond Pulsars

Abstract We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821−24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at >3σ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821−24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821−24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission.