High Excitation Energy Research Articles

Excimer formation and site selectivity in single pyrene microcrystals

Thin microcrystals of pyrene have been recrystallized by using a surfactant. With a size-range of several hundred nm to a few micrometers, the crystals have been characterized by using standard techniques of X-ray and Raman spectroscopy besides the atomic force and scanning electron microscopy. The fluorescence microscopy of single microcrystal shows fluorescence due to monomer as well as the red-shifted broad, structureless excimer-type emission. The observed decay profiles of the red-shifted emission reveal existence of dimer and higher aggregates in the crystalline state when excited at the red-edge of the absorption band. This is in contrast to the excimer emission observed at higher energy excitation range corresponding to the monomer absorption. Distinctly different nature of time-resolved decay profiles differentiates the two mechanisms. The observations have been used to propose existence of different sites of crystal packing under two different excitations (370 nm and 408 nm). The structural anisotropy of these crystals makes them useful as a probe in crystal structure based molecular and biological sensing.

Luminescence properties of CsPbBr3 single crystals and CsPbBr3 crystalline phases dispersed in a KBr matrix

Spectra of steady-state X-ray excited luminescence (XEL) and thermally stimulated luminescence (TSL) of CsPbBr3 single crystals in the temperature range of 80–294 K were studied. Each of the measured XEL spectra of CsPbBr3 single crystal contain only one elementary band peaking at 535 nm, which can be attributed to the radiative decay of the matrix exciton. The activation energy of exponential luminescence thermal quenching in this range, as determined by Mott's formula, is equal to 75 meV, close to the hole trap depth of 110 meV obtained for the main TSL peak of this crystal at 125 K. This value of the XEL quenching activation energy is associated with the thermal deactivation of the exciton hole component in the CsPbBr3 matrix.Doping of KBr crystals with CsPbBr3 perovskite impurities (0.05–1 mol. %) leads to the formation of CsPbBr3 micro- and nanocrystals in a KBr matrix with characteristic spectra of exciton photo- and XEL luminescence. A five-fold increase in the intensity of XEL was registered in KBr: CsPbBr3 (0.05 mol. %) samples at 294 K compared to that of CsPbBr3 single crystal.The temperature dependence of the XEL intensity of KBr: CsPbBr3 crystals and the analysis of their TSL integral curves allow us to make a conclusion about the hole mechanism of high-energy excitation energy transfer from the matrix to the activator resulting in the appearance of typical exciton luminescence in CsPbBr3 nanoparticles.

Shell effect on fission fragment mass distribution at Ecn* up to 70 MeV: Role of multichance fission

Mass distributions of fission fragments produced from the $^{249}\mathrm{Bk}$ compound nucleus (CN), populated by complete fusion of $^{11}\mathrm{B}$ with $^{238}\mathrm{U}$, were measured for the excitation energies in the range of ${E}_{\mathrm{cn}}^{*}\ensuremath{\approx}36.7--69.7$ MeV. Nearly flat tops observed for these distributions indicate the presence of asymmetric fission, contrary to the pure Gaussian mass distributions expected at such high excitation energies. A fit to the mass distribution using three Gaussian functions provides an estimate of individual contributions from symmetric and asymmetric modes of fission. A significant contribution of the asymmetric component observed at CN excitation energies above 40 MeV can be understood only by invoking ``multichance fission'' in the calculations using the semiempirical model code gef. A systematic analysis of the mass distributions for several heavy transuranic nuclei reveals that the manifestation of the fragment shell effect in the integral mass distributions are visible even up to an initial compound nucleus excitation of ${E}_{\mathrm{cn}}^{*}\ensuremath{\approx}70$ MeV due to their influence on the distributions of higher chance fissions.

Thermal stimulated structural transformation of cubic Zn0.78Cd0.22S nanoparticles to ZnO nano-hexagons: Tailoring of optical band gap and emission spectra for optoelectronic implementations

Ternary alloys of Zn0.78Cd0.22S nanoparticles (NPs) are synthesized via the facile co-precipitation technique. The as-synthesized sample exhibits a zincblende-type cubic phase with an average crystalline size of 2 nm. Thermal annealing and UV irradiation are utilized as post-treatment processes for tailoring the optical properties of Zn0.78Cd0.22S NPs. The as-synthesized sample exhibits a stable cubic phase up to 400 °C, during which partial phase transformation to a hexagonal structure is observed at a higher temperature of 500 °C. The oxidation of Zn0.78Cd0.22S NPs to mixed oxide phases with the majority of ZnO begins at 600 °C which induces morphology transformation to a relatively large nano-hexagon with a single crystalline domain size. The increase of the annealing temperature is accompanied by a decrease of Zn0.78Cd0.22S NPs optical band gap (Eg) due to the weakness of size confinement as well as the formation of localized states below the mobility band edges. The brief UV irradiation results in the increase of Eg whereas a further increase in exposure time is accompanied by a reduction of Eg. The photoluminescence (PL) spectrum of the as-synthesized sample covers a wide spectral range from UV to visible. Thermal annealing has a slight effect on the PL emission at high excitation energy, whereas low excitation energy reveals higher sensitivity to deep-state emission. Thermal oxidation incorporates a high concentration of oxygen-related defects that induce strong enhancement in the green emission at the expense of UV emission. This indicates the thermal-induced bleaching of shallow trapping sites and the evolution of other deep trapping or recombination sites.

Coexistence of single-particle and collective excitation in Ni61

The high spin states in 61 Ni have been studied using the fusion evaporation reaction, Ti( $^{14}$C,3n) $^{61}$Ni at an incident beam energy of 40 MeV. A Compton suppressed multi-HPGe detector setup, consisting of six Clover detectors and three single crystal HPGe detectors was used to detect the de-exciting $\gamma$ rays from the excited states. The level scheme has been extended up to an excitation energy of 12.8 MeV and a tentative J$_{\pi}$ = 35/2$^+$ . The low-lying negative parity levels are found to be generated by single particle excitation within the f p shell and also excitations to the g$_{9/2}$ orbitals as explained well with shell model calculations using the GXPF1Br+V M U (modified) interaction. Two rotational structure of regular E2 sequences with small to moderate axial deformation have been established at higher excitation energy. Most interestingly, two sequences of M1 transitions are reported for the first time and described as magnetic rotational bands. The shears mechanism for both the bands can be described satisfactorily by the geometrical model. The shell model calculation involving the cross shell excitation beyond the fp shell well reproduce the M1 and E2 sequences. The shell model predicted B(M1) values for the magnetic rotational band B1 show the decreasing trend with spin as expected with closing of the shears.

Plasmon Effects in Non-Diagram X- Ray Spectra of Calcium (Ca) and Cobalt (Co)

In recent years the whole area of high energy excitations in solid has flourished well, both experimentally and theoretically. Their spectroscopy and theoretical understanding have important implications for the knowledge of the structure and properties of materials, both in bulk and near the surface. The theory used in the present work, relates to origin of Non-diagram X-ray spectra in various excitation processes where a deep as well as the surface electron is excited. The specific contributions of the intrinsic as well as the extrinsic ‘Plasmon-coupling’ processes have been obtained theoretically in terms of “Non-diagram-to-parent-diagram X-ray line yield ratios” for the high energy plasmon satellite profiles in the X-ray line spectra of Kα L(0) main lines in Calcium (Ca) and Cobalt (Co) by extending the Bohm-Pines Hamiltonian and using many body theory. It has been shown that the high-energy X-ray satellite line shapes of Calcium (Ca) and Cobalt (Co) observed by Mauron and Douss are due to the Plasmon Oscillations. The theoretically calculated results have been probed by comparing to the relative satellite yields obtained by Mauron and Dousse and are found to agree well with their experimentally observed values.

Dynamics of the fractional quantum Hall edge probed by stroboscope measurements of trions

By using observations from pump-probe stroboscopic confocal microscopy and spectroscopy, we demonstrate the dynamics of trions and the fractional quantum Hall edge on the order of ∼1 ps. The propagation of the quantum Hall edge state excited by a voltage pulse is detected as a temporal change in reflectance in the downstream edge probed by optical pulses synchronized with the voltage pulse. The temporal resolution of such stroboscopic pump-probe measurements is as fast as the duration time of the probe pulse (∼1 ps). This ultra-fast stroboscope measurement enables us to distinguish between the normal mode of edge excitation, known as the edge magneto-plasmon or charge density wave, and other high-energy non-linear excitations. This is the only experimental method available to study the ultra-fast dynamics of quantum Hall edges and makes it possible to derive the metric tensor gμν of the (1+1)=2-dimensional curved spacetime in quantum universe and black hole analogs implemented in the quantum Hall edge.

Fission dynamics of excited compound nuclei in a wide range of fissile parameters produced in O16,18+X reactions within a stochastic approach

A stochastic approach based on four-dimensional Langevin equations has been used to simulate the fission dynamics of the excited compound nuclei $^{256}\mathrm{Fm}, ^{254}\mathrm{Fm}, ^{224}\mathrm{Th}, ^{215}\mathrm{Fr}, ^{213}\mathrm{Fr}, ^{200}\mathrm{Pb}, ^{187}\mathrm{Ir}, ^{172}\mathrm{Yb}, ^{170}\mathrm{Yb}, ^{162}\mathrm{Yb}, ^{142}\mathrm{Ce}$, and $^{125}\mathrm{Cs}$ produced in ${}^{16,18}\mathrm{O}+X$ reactions with projectile energies 158.8 and 288 MeV. The effect of nuclear dissipation was investigated in the dynamical simulation of fission process of these nuclei. The average prescission neutron multiplicity, the fission time, the average total kinetic energy of fission fragments, the mass and energy distribution of fission fragments, and the variation of the prescission neutron multiplicity with total kinetic energy of fission fragments have been calculated for these nuclei. The dynamical calculations have taken into account not only three shape collective coordinates introduced on the basis of the ``funny hills'' shape parameters but also orientation degree of freedom (spin about the symmetry axis), and in the dynamical calculations dissipation generated through the chaos-weighted wall and window friction formula and also the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction. Furthermore, the effect of dissipation coefficient of $K, {\ensuremath{\gamma}}_{K}$, were also considered in the dynamical calculations. Comparison of the theoretical results with the experimental data shows that the experimental data for compound nuclei produced with the projectile energy 158.8 MeV can be reproduced satisfactorily with the results of calculations by using the chaos-weighted wall and window friction formula, although the results of calculations of the average prescission neutron multiplicity, the fission time, and the variation of the pre-scission neutron multiplicity with total kinetic energy of fission fragments lie somewhat below the experimental data for heavy nuclei produced in reactions with projectile energy ${E}_{\mathrm{lab}}=158.8\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and also for compound nuclei produced with the projectile energy 288 MeV. It was also shown that for reproducing experimental data for heavy nuclei produced in reactions with projectile energy ${E}_{\mathrm{lab}}=158.8\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and also for nuclei produced with projectile energy ${E}_{\mathrm{lab}}=288\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ is suitable to use the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction in the Langevin equations. In other words, for simulations of fission dynamics of nuclei at high excitation energies and also for heavy nuclei it is suitable to use the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction in the Langevin equations.

Nonadiabatic dynamics in a forest of coupled states: Electronic state branching in the VUV photodissociation of N2.

Multi-state electronic dynamics at higher excitation energies is needed for the understanding of a variety of energy rich situations, including chemistry under extreme conditions, vacuum ultraviolet (VUV) induced astrochemistry, and attochemistry. It calls for an understanding of three stages, energy acquisition, dynamical propagation, and disposal. It is typically not possible to identify a basis of uncoupled quantum states that is sufficient for the three stages. The handicap is the large number of coupled quantum states that is needed to describe the system. Progress in quantum chemistry provides the necessary background to the energetics and the coupling. Progress in quantum dynamics takes this as input for the propagation in time. Right now, it seems that we have come of age with potential detailed applications. We here report a demonstration to a coupled electron-nuclear quantum dynamics through a maze of 47 electronic states and with attention to the order in perturbation theory that is indicated using propensity rules for couplings. Close agreement with experimental results for the VUV photodissociation of 14N2 and its isotopomer 14N15N is achieved. We pay special attention to the coupling between two dissociative continua and an optically accessible bound domain. The computations reproduce and interpret the non-monotonic branching between the two exit channels producing N(2D) and N(2P) atoms as a function of excitation energy and its variation with the mass.

Excited states of zero seniority based on a pair condensate

We study the excited states of zero seniority for various like-particle systems interacting by pairing forces and by general two-body interactions. We consider two types of excitations, generated from a ground state described by a pair condensate. One type is obtained by breaking a pair from the ground state condensate and replacing it by "excited" collective pairs built on time-reversed single-particle orbits. The second type of zero seniority excited states is described by a condensate of identical excited pairs. The structure of these excited states is analysed for the picked fence model and for the valence neutrons of $^{108}$Sn. For a state-depending pairing interaction, the first type of excited states agree well with the J=0 states which are known in $^{108}$Sn. At the same time, these states can be also associated unambiguously with those exact states which are the closest in energy to the experimental levels. The states corresponding to the excited pair condensate appear at low energies, around the energy of the second excited state of the first type, and they do not have a simple correspondence with exact eigenstates. However, at a much higher excitation energy there is an exact state which is similar in structure to an EPC state. It is shown that this EPC state has the features of a giant pairing vibration.

Ce3+ Doped Al2O3-YAG Eutectic as an Efficient Light Converter for White LEDs

Ce3+ doped Al2O3-YAG eutectics were successfully grown by the horizontal directional crystallization method. The crystallization rate of eutectic growth was changed in the 1-7.5 mm/h range at a growth temperature of 1835 ℃. The microstructure of eutectic samples was investigated using scanning electron microscopy and X-ray microtomography. The intrinsic morphology of eutectic represents the stripe-like channel structure with a random distribution of the garnet Y3Al5O12 (YAG) and Al2O3 (sapphire) phases. The content of these phases in the stripes changes in the 52.9-55.3% and 46.1-47.1% ratios, respectively, depending on the growth rate of the crystallization of the eutectic samples. The luminescent properties of the eutectic demonstrated the dominant Ce3+ luminescence in the garnet phase. The luminescence of the Ce3+ ions in Al2O3 has also been observed and the effective energy transfer processes between Ce3+ ions in the Al2O3 and YAG garnet phases were revealed under high-energy excitation and excitation in the UV Ce3+ absorption bands of sapphire. The phosphor conversion properties and the color characteristics (Al2O3-YAG):Ce eutectic with different thicknesses were investigated under excitation by a blue LED. We have also tested the prototypes of white LEDs, prepared using a blue 450 nm LED chip and (Al2O3-YAG):Ce eutectic photoconverters with 0.15 to 1 mm thicknesses. The results of the tests are promising and can be used for the creation of photoconverters for high-power white LEDs.

Quantitative analysis of energy loss processes for the core level intensities in hard X-ray photoemission

Hard X-ray Photoemission spectra (HAXPES) for Al films on Si substrates were measured, and thickness dependence of the Al and Si core level spectra was obtained. A quantitative analysis of the plasmon-loss processes and the continuous background was performed. Such loss process can be quantitatively understood using a HAXPES analysis, especially for the intensity analysis of the core levels. Si 1 s electrons excite extrinsic Al plasmons and continuous loss features as far as they propagate within the Al film. The results give us important information and enable us to separate the intrinsic, extrinsic and their interference effects in plasmon-loss processes. Even for the high energy excitation inherent to HAXPES, the interference effect between intrinsic and extrinsic plasmon-losses is shown to be not negligible. A stronger contribution from loss features than from the main peaks should be considered for quantitative analysis.

Fission as a relevant probe of the nuclear level density away from β-stability

Fission at moderate to high excitation energy is proposed as an innovative approach to study the evolution of the nuclear level density (NLD) away from β-stability. A four-dimensional dynamical Langevin model, implementing various prescriptions of the asymptotic level-density parameter a˜, is employed to demonstrate the relevance of considering typical fission observables, and namely the pre- and post-scission neutron multiplicities, to investigate the evolution of a˜ with N and Z. The richness of fission is shown to offer an alternative route, that is very complementary to the conventional fusion-evaporation method from which no consensus emerged yet. In particular, to investigate the isospin-dependence of the NLD, the present calculations lead us to propose a series of fusion-induced fission measurements based on Ca + Pb collisions which are readily available at current experimental facilities. This set of reactions can be further enhanced with today, as well as future, radioactive beams.

New measurement of 4He and proton decays from resonant states in 19Ne* *Supported by the National Key R & D Program of China (2018YFA0404403, 2022YFA1602302), the National Natural Science Foundation of China (11875074, 11875073, 12235020, 12027809, 11961141003, U1967201, U2167204, 11775004, 11775003), the Continuous Basic Scientific Research Project (WDJC-2019-13), the State Key Laboratory of Nuclear Physics and Technology, Peking University (NPT2020KFY10),

A Li(O,Ne)H multi-nucleon transfer-reaction experiment was performed to populate the highly excited states in Ne. The subsequent decay particles, He or protons from the Ne resonant states, were detected in coincidence with the recoil H. The excitation-energy spectra of Ne were reconstructed using the detected proton or He and the deduced F or O data, respectively. A broad resonance at about 7.85 MeV (1/2) was observed, with partial decay widths different from the previously reported values, which may have a significant impact on the destruction of F in astrophysical processes. Several resonances up to very high excitation energies have been identified with a large α-clustering strength, which confirm the formation of the cluster structure with a one-hole configuration in light nuclei and encourage further systematic studies of the cluster structure in Ne.

Excitation-Wavelength-Dependent Charge-Carrier Lifetime in Hematite: An Insight from Nonadiabatic Molecular Dynamics.

Experiments have reported that the photoexcited carrier lifetime in α-Fe2O3 has a significant excitation-wavelength dependence but leave the physical mechanism unresolved. In this work, we rationalize the puzzling excitation-wavelength dependence of the photoexcited carrier dynamics in Fe2O3 by performing nonadiabatic molecular dynamics simulation based on the strongly constrained and appropriately normed functional, which accurately describes the electronic structure of Fe2O3. Photogenerated electrons with lower-energy excitation relax fast in the t2g conduction band within about 100 fs, while the photogenerated electrons with higher-energy excitation undergo first a slower interband relaxation from the eg lower state to the t2g upper state on a time scale of 135 ps, followed by the much faster t2g intraband relaxation. This study provides insight into the experimentally reported excitation-wavelength dependence of the carrier lifetime in Fe2O3 and a reference for regulating photogenerated carrier dynamics in transition-metal oxides through the light excitation wavelength.

Spiroborate-Based Host Materials with High Triplet Energies and Ambipolar Charge-Transport Properties.

Organic light-emitting diodes (OLEDs) receive considerable attention because of their commercial use in flat panel displays. Herein, highly efficient spiroborate-based host materials are reported for use in blue OLEDs. Our designed spiroborates (SBOX) were simple to synthesize and exhibited high triplet excitation energies, narrow S-T gaps, and balanced charge carrier mobilities. A blue OLED containing one of the designed spiroborates, SBON, as a host exhibited a high external quantum efficiency (27.6 %) and low turn-on voltage (3.7 V) compared to those observed using 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (17.6 % and 4.5 V, respectively), indicating their potential as host materials in OLEDs.

Spiroborate‐Based Host Materials with High Triplet Energies and Ambipolar Charge‐Transport Properties

AbstractOrganic light‐emitting diodes (OLEDs) receive considerable attention because of their commercial use in flat panel displays. Herein, highly efficient spiroborate‐based host materials are reported for use in blue OLEDs. Our designed spiroborates (SBOX) were simple to synthesize and exhibited high triplet excitation energies, narrow S‐T gaps, and balanced charge carrier mobilities. A blue OLED containing one of the designed spiroborates, SBON, as a host exhibited a high external quantum efficiency (27.6 %) and low turn‐on voltage (3.7 V) compared to those observed using 3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (17.6 % and 4.5 V, respectively), indicating their potential as host materials in OLEDs.

High-energy spin excitations in the quantum spin liquid candidate Zn-substituted barlowite probed by resonant inelastic x-ray scattering

A quantum spin liquid is a novel ground state that can support long-range entanglement between magnetic moments, resulting in exotic spin excitations involving fractionalized $S=\frac{1}{2}$ spinons. Here, we measure the excitations in single crystals of the spin liquid candidate Zn-barlowite using resonant inelastic x-ray scattering. By analyzing the incident polarization and temperature dependences, we deduce a clear magnetic scattering contribution forming a broad continuum that surprisingly extends up to $\ensuremath{\sim}200$ meV ($\ensuremath{\sim}14J$, where $J$ is the magnetic exchange). The excitation spectrum indicates that significant contributions may arise from multiple pairs of spinons and/or antispinons at high energies. Furthermore, the observation of similar scattering in the hexagonal barlowite parent material above its ordering temperature suggests the presence of similar high-energy excitations, irrespective of the low-energy physics.

Three-body calculations of β decay applied to Li11

A novel practical few-body method is formulated to include isospin symmetry for nuclear halo structures. The method is designed to describe $\ensuremath{\beta}$ decay, where the basic concept of isospin symmetry facilitates a proper understanding. Both isobaric analog and antianalog states are treated. We derive general and explicit formulas for three-body systems using hyperspherical coordinates. The example of the $\ensuremath{\beta}$ decaying $^{11}\mathrm{Li}$ ($^{9}\mathrm{Li}+n+n$) is chosen as a challenging application for numerical calculations of practical interest. The detailed results are compared to existing experimental data, and good agreement is found at high excitation energies, where the isobaric analog and antianalog states are situated in the daughter nucleus. An interpretation of the decay pattern at lower excitation energies is suggested. Decays of the $^{9}\mathrm{Li}$ core and the two halo neutrons are individually treated and combined with the daughter system with almost unique isospin, which we predict to be broken by about $0.4%$ probability. Properties of decay products are predicted as possible future tests of this model.

Hydrazineylidene‐3‐oxopropanal derivatives as antiviral agents for treatment of HBV and HCV: Experimental, DFT, and molecular docking studies

AbstractIn this study, two derivatives of hydrazineylidene‐3‐oxopropanal: chlorophenyl (CPHO) and Nitrophenyl (NPHO) substituted hydrazineylidene compounds were synthesized, spectroscopically characterized using (FT‐IR, UV, and NMR), and theoretically modelled as a potential drug for the treatment of antiviral hepatitis (HBV and HCV) using in‐sillico molecular docking approach. Electronic structure investigation based on density functional theory (DFT) at the B3LYP/6‐311++G(d,p) level of theory was conducted for the investigation of the structural, reactivities, and electronic properties of the studied compounds. The FT‐IR analysis in gas, water, ethanol and DMSO indicates a maximum stretching vibrations frequencies of C‐H in NPHO between 3249.38 to 3254.77 cm‐1 and 3236.04 to 3240.66 cm‐1 for CPHO, N‐H for NPHO is 3309.81 to 3336.37 cm‐1, and CPHO is 3330.11 to 3331.18 cm‐1, C=O in NPHO to be 1685.55 to 1705.60 cm‐1, and 1700.31 to 1679.15 cm‐1 for CPHO. The C‐N stretching vibrations in NPHO were 1519.98 to 1562.06 cm‐1 and 1430.05 to 1460.33 cm‐1 for CPHO. The UV‐Vis analysis indicates that NPHO wavelength absorption spectrum showed high excitation energy bands between 369.74 to 440.60 nm and CPHO at 178.95 to 434.08 nm. The highest stabilization energy of NPHO is LP (1) N12 donor and LP*(1) H10 acceptor with a value of 417.54 kcal/mol compared to πC17 ‐ O18 donor and π*C19 ‐ C28 acceptor with a value of 108.33 kcal/mol for CPHO. The molecular binding affinity of CPHO and NPHO had a high mean binding affinity of ‐5.83 and ‐6.05 kcal/mol, compared to the standard antiviral drugs with ‐5.00 kcal/mol. Therefore, the compounds show excellent reactivity based on the electronic structure, spectroscopic characterization and represent a potential antiviral agent treatment for HBV and HCV.