Transition Oscillator Strengths Research Articles

Oscillator strengths and cross sections of the valence-shell excitations of CH[formula omitted]I studied by fast electron scattering

Oscillator strengths and cross sections of the valence-shell excitations in CH3I are important for studying molecular photodissociation and monitoring the destruction of ozone in the Earth’s atmosphere. Based on the relative flow technique, absolute generalized oscillator strengths of the valence-shell excitations in CH3I have been determined by using an angle-resolved electron energy loss spectrometer. The measurement was carried out at an incident electron energy of 1.5 keV and an energy resolution of 80 meV. Optical oscillator strengths for the dipole-allowed transitions have been obtained at the zero limit of the squared momentum transfer, providing an independent cross check with the previous experimental results. The integral cross sections from the excitation threshold to 5000 eV have also been obtained by means of the BE-scaling method. The present experimental oscillator strengths and cross sections can supplement the fundamental spectroscopic data of CH3I and will play an important role in the studies of molecular photodissociation dynamics.

Pressure Engineering Toward Harvesting the Bright Deep‐Blue‐Light Emission in Y‐based Metal‐Organic Frameworks

AbstractThe emergence of metal‐organic frameworks (MOFs) provides a new platform of low‐cost and color‐saturated blue light‐emitting diodes ideal for display and solid‐state lighting applications. However, numerous established MOFs still exhibit weak deep‐blue‐light emission (<450 nm) owing to low energy/charge transfer efficiency. Here a pressure‐treated strategy to greatly enhance photoluminescence performance of deep‐blue light‐emitting Y(BTC)(H2O)6 (H3BTC: benzene‐1,3,5‐tricarboxylic acid) is reported. Pressure‐treated Y(BTC)(H2O)6 exhibits a bright emission at 409 nm with a photoluminescence quantum yield from the initial 2.8% increasing to 75.0%. The hydrogen bonding cooperativity effect increases hydrogen bond binding energy after pressure treatment and thus the planarization structure is locked. The increased electronic transition diversity and oscillator strength originating from the planarization structure are highly responsible for boosting metal‐to‐ligand charge transfer. The findings in this study provide significant insights into the underlying mechanism of the structure‐property relationship in Y(BTC)(H2O)6 and offer a promising strategy to harvest deep‐blue‐emitting MOFs materials.

Analysis of line intensity ratio for optical transitions of 3d6 levels and plasma screening effect on atomic structure of Fe III ion

Iron emission lines are observed from most classes of astronomical objects through a wide spectral range from infrared to X-ray. For a useful analysis of these lines, accurate atomic data for neutral iron and its ions is required. In this work, we have done calculations of energy levels and radiative data of Fe III by using the relativistic configuration interaction method with the implementation of the flexible atomic code (FAC). We have calculated emission-line intensity ratios for optical transitions among the fine-structure levels of the 3d6 configuration at temperature 104 K and density ne=104cm−3. We have also compared our results with the observed spectra of Herbig-Haro objects HH 202 of Orion Nebula, Planetary Nebula, and NGC 2392, post-asymptotic giant branch star (PAGB) HD341617. We have also discussed various discrepancies between the observed spectra from these nebulae and our calculations. The atomic structure of plasma-embedded Fe III is also analyzed using flexible atomic code (FAC). The graphical study shows that transition wavelengths, oscillator strengths, and transition rates are very sensitive to the plasma environment in the density range 1021cm−3 to 5×1022cm−3 and spectral lines associated to Δn = 0 transitions for Fe III ion are blueshifted. We have also studied the dependence of emission line intensity ratios on plasma density and temperature. We believe that our presented results are useful in spectroscopic analysis and examination of astrophysical and laboratory plasma.

Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal SixGe1−x alloys

Ge-rich hexagonal SiGe alloys have recently emerged as new direct-gap semiconductors with unprecedented potential for integration of photonics on silicon. We present a comprehensive first-principles investigation of optical, transport, and thermoelectric properties of pure and doped hexagonal ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ alloys based on density-functional theory calculations, the Boltzmann transport equation, and the generalized quasichemical approximation to obtain alloy averages of electronic properties. At low temperatures, phase decomposition into the hexagonal elementary crystals is thermodynamically favored, but around and above room temperature random alloys are predicted to be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge is direct with very weak optical transitions at the absorption edge. The alloy band gap remains direct for a Si content below 45% and the oscillator strength of the lowest optical transitions is efficiently enhanced by alloying. The optical spectra show clear trends and both absorption edges and prominent peaks can be tuned with composition. The dependence of transport coefficients on carrier concentration and temperature is similar in cubic and hexagonal alloys. However, the latter display an anisotropic response due to the reduced hexagonal symmetry. In particular, the transport mass exhibits a significant directional dependence. Seebeck coefficients and thermoelectric power factors of $n$-doped alloys show nonmonotonous variations with the Si content independently of temperature.

Synthesis, Quantum Computational Analysis and Molecular Docking of 3-(2-Hydroxyphenyl)-1-Phenyl Propanone: A Combined Experimental and Theoretical Analysis

The newly synthesized 3-(2-Hydroxyphenyl)-1-phenyl propenone was analyzed. In this work, optimization of the 3-(2-hydroxyphenyl)-1-phenyl propanone was carried out with DFT using B3LYP method utilizing 6-311++G(d,p) basis set. The structure parameters of the compounds as molecular geometry, bond lengths, bond angles, atomic charge, and HOMO-LUMO energy gap have been investigated and compound with the reported experimental results. The donor and acceptor interactions in 3-(2-Hydroxyphenyl)-1-phenyl propenone were investigated using natural bond orbital (NBO) analysis. By matching the obtained UV-Vis spectra to the time-dependent (TD)-DFT analysis, the energies of band gap, absorption wavelength, and oscillatory strength of 3-(2-Hydroxyphenyl)-1-phenyl propenone were found. Density of states for total (TDOS), partial (PDOS), and also overlap population (OPDOS) analysis were obtained. Molecular electrostatic potential (MEP) provides the information on the electrophilic, nucleophilic, and free radical prone reactive sites of the molecule. Non-linear optical features were demonstrated from the first-order hyperpolarizability. Based on the above results the 3-(2-Hydroxyphenyl)-1-phenyl propenone compound was investigated for further biological investigation. TD-DFT analysis was also performed to calculate energies, oscillator strength of electronic singlet-singlet transitions, and the absorption wavelengths. The Molecular docking (ligand-protein) simulations have been performed using the Auto Dock version 4.2.6.

A Configurationally Confined Thermally Activated Delayed Fluorescent Two‐Coordinate CuI Complex for Efficient Blue Electroluminescence

AbstractThermally activated delayed fluorescence (TADF) from linear two‐coordinate coinage metal complexes is sensitive to the geometric arrangement of the ligands. Herein we realize the tuning of configuration from coplanar to orthogonal gradually by variation of substituents. In a complex with confined twist configuration, its blue emission peaking at 458 nm presents a high ΦPL of 0.74 and a short τTADF of 1.9 μs, which indicates a fast enough kr,TADF of 3.9×105 s−1 and a depressed knr of 1.4×105 s−1. Such outstanding luminescent properties are attributed to the proper overlap of HOMO and LUMO on CuI d orbitals that guarantees not only small ΔEST but also sufficient transition oscillator strength for fast . Vacuum‐deposited blue OLEDs with either doped or host‐free emissive layer present external quantum efficiencies over 20 % and 10 %, respectively, demonstrating the practicality of the configurationally confined strategy for efficient linear CuI TADF emitters.

A Configurationally Confined Thermally Activated Delayed Fluorescent Two-Coordinate CuI Complex for Efficient Blue Electroluminescence.

Thermally activated delayed fluorescence (TADF) from linear two-coordinate coinage metal complexes is sensitive to the geometric arrangement of the ligands. Herein we realize the tuning of configuration from coplanar to orthogonal gradually by variation of substituents. In a complex with confined twist configuration, its blue emission peaking at 458 nm presents a high ΦPL of 0.74 and a short τTADF of 1.9 μs, which indicates a fast enough kr,TADF of 3.9×105 s-1 and a depressed knr of 1.4×105 s-1 . Such outstanding luminescent properties are attributed to the proper overlap of HOMO and LUMO on CuI d orbitals that guarantees not only small ΔEST but also sufficient transition oscillator strength for fast . Vacuum-deposited blue OLEDs with either doped or host-free emissive layer present external quantum efficiencies over 20 % and 10 %, respectively, demonstrating the practicality of the configurationally confined strategy for efficient linear CuI TADF emitters.

Effects of electric field and hydrostatic pressure on the exciton states in strained zinc-blende In[formula omitted]Ga[formula omitted]N-GaN coupled double quantum wells

Based on the effective mass approximation, the variational theory study of the exciton properties in a strained zinc blende GaN/InxGa1−xN/GaN/InyGa1−yN/GaN coupled double quantum well is presented considering the combined effects of hydrostatic pressure, strain, and external electric field. The results show that the exciton binding energy first increases, it achieves a maximum value, and then decreases with the reduction of the well width. Contrarily, the exciton binding energy decreases slightly first, it reaches a minimum value, and then increase gradually until a constant with the enhancement of the middle barrier thickness. Meantime, the pronounced dependencies of the exciton binding energy, interband transition energy, emission wavelength, oscillator strength, and radiation decay time of the coupled double quantum well on hydrostatic pressure are analyzed systematically. As the hydrostatic pressure increases, the exciton binding energy increases linearly, and the interband transition energy (emission wavelength) is proportional (inversely) to hydrostatic pressure. In addition, the variation of the exciton binding energy and Stark shift with the external electric field is explored detailedly.

Experimental branching fractions, transition probabilities, and oscillator strengths in Ni I

Experimental branching fractions of 56 Ni I lines in region of 202.659–663.974 nm are reported by the emission spectrum. A hollow cathode discharge lamp was used as a light source to produce free atoms and a grating spectrometer recorded the intensity–calibrated spectra. Combining branching fraction from the record spectra data with published radiative lifetimes measured by time–resolved laser–induced fluorescence (TR–LIF) technique, absolute transition probabilities and oscillator strengths were determined. Generally good agreement is found when comparing with previously reported oscillator strengths of Ni I.

Study of electron impact excitation of H-like Si13+ ion in dense plasma environment

The relativistic configuration interaction technique has been employed to study the electron impact excitation collision strengths of H-like Si13+ ion in strongly coupled plasma environment. The analytical plasma screening b-potential has been adopted to determine the physical effects of the screened Coulomb interaction due to the influence of plasma on the atomic structure and dynamics affecting atomic processes. The modified Dirac equations are solved to obtain the bound and continuum state wave functions. We examine the plasma screening effect by considering the plasma conditions at the electron temperatures of 200, 600 and 1000 eV over electron density range of 2.0 × 1023 - 1.0 × 1024 cm−3. The present results highlight that the inclusion of plasma environment induces significant effect on the binding energies, transition energies, radiative transition probabilities, oscillator strengths and collision strengths. It has been observed that the collision strength decreases with increase in plasma electron density for a fixed temperature. Our results will be beneficial for laser produced plasmas, high energy density physics, astrophysical applications and will open the door to modelling and advanced diagnostics of solar and stellar plasmas.

4-Cyanotryptophan as a Sensitive Fluorescence Probe of Local Electric Field of Proteins.

Electrostatic interactions are key determinants of protein structure, dynamics, and function. Since protein electrostatics are nonuniform, assessment of the internal electric fields (EFs) of proteins requires spatial resolution at the amino acid residue level. In this regard, vibrational Stark spectroscopy, in conjunction with various unnatural amino acid-based vibrational probes, has become a common method for site-specific interrogation of protein EFs. However, application of this method is often limited to proteins with relatively high solubility, due to the intrinsically low oscillator strength of vibrational transitions. Therefore, it would be useful to develop an alternative method that can overcome this limitation. To this end, we show that, using solvatochromic study and molecular dynamics simulations, the frequency of maximum emission intensity of the fluorophore of 4-cyanotryptophan (4CN-Trp), 3-methyl-1H-indole-4-carbonitrile, exhibits a linear dependence on the local EF. Since the absorption and emission spectra of 4CN-Trp are easily distinguishable from those of naturally occurring aromatic amino acids, we believe that this linear relationship provides an easier and more sensitive means to determine the local EF of proteins.

Theoretical study of the spectroscopy and radiative transition probabilities of Si2 from visible to infrared.

High level ab initio calculations on the electronic states of a silicon dimer (Si2) have been carried out by employing a multi-reference configuration interaction plus Davidson correction (MRCI + Q) approach with the aug-cc-pVQZ basis set. The scalar relativistic correction is taken into consideration by the second-order Douglas-Kroll-Hess approximation. In the present work, the transition properties (oscillator strength, Einstein spontaneous emission coefficient and radiative lifetime) of the singlet-singlet, triplet-triplet, and quintet-quintet transitions of Si2 are discussed. We emphasize the triplet-triplet emission bands H3Σ-u-X3Σ-g, K3Σ-u-X3Σ-g and D3Πu-L3Πg which are dominant for 0-11 (18 822 cm-1), 0-0 (30 672 cm-1), and 0-0 (28 881 cm-1) transitions, respectively. In addition, the strong experimentally observed b1Πu-d1Σ+g band around 4184 cm-1 corresponds to the second 1Σ+g-b1Πu combination in the infrared region. The calculated oscillator strengths of the singlet-singlet transitions (f1Πg-e1Σ-u, 21Πg-b1Πu, b1Πu-d1Σ+g and g1Δu-a1Δg) are in the order of 10-3. From a theoretical point of view, the 0-0 sub-band for the f1Πg-e1Σ-u transition, 0-7 for 21Πg-b1Πu, 0-0 for b1Πu-d1Σ+g and the 0-7 vibronic bands for the g1Δu-a1Δg transition may be observed experimentally. It is expected that the present results could provide theoretical support for a deeper understanding of the experimental Si2 spectra providing further applications in astrophysics.

Hydrogen-like donor impurity states in strongly prolate ellipsoidal quantum dot

In the current article, the binding energy and impurity-related photoionization cross-section are investigated for the case of an infinite confinement potential well model using a variational approach for hydrogen-like impurity states in strongly prolate ellipsoidal quantum dot. The binding energy is calculated as a function of ellipsoidal small and large semiaxes and as a function of impurity displacement. The behavior of the oscillator strength for the quantum transitions between the impurity ground state and the first two non-impurity states are considered for different values of incident light angles and geometrical parameters. In the work, we illustrate the results of photoionization cross-section computations depending on the incident photon energy for a range of incident angles and different values of impurity shift. It is revealed that the threshold frequency decreases with the increase of impurity displacement.

Extensive study on the optical and structural characteristics of Nd3+ doped Lead-Borate-Strontium-Tungsten glass system: Judd–Ofelt analysis

In this paper, a neodymium doped Lead-Borate-Strontium-Tungsten glass system is synthesized by melt - quenching method. The samples are fabricated according to the composition 45B2O3-45PbO-7SrO-(3-x)WO3-(x)Nd2O3, where x = 0, 1, 1.5, 2 and 2.5 mol%. As the neodymium ion concentration is increased, the measured density and molar volume of the glass is observed to increase. Raman spectroscopy and FTIR measurements were conducted to study the structure of the glass system and examine modifications that occurred by adding various Nd3+ ion concentrations. FTIR and Raman analysis revealed vibration and bonds stretching of various borate groups. UV–Vis–NIR spectroscopic measurement displays 6 absorption bands and was used to evaluate refractive indices, optical bandgap energies and other associated parameters. The J–O intensity parameters of Nd3+ions are evaluated. The obtained intensity parameters exhibited a trend which follows Ω2 > Ω4 > Ω6 for all samples. Additionally, the experimental and theoretical oscillator strengths of the radiative 4f transitions, refractive indices(n), branching ratio(β) and lifetimes(τ) were determined. The spectroscopic quality factor obtained suggests the suitability for the glass system to be used in photonic applications.

Spectral properties of a broadband far infrared photodetector with a new design of active region

A quantum theory of spectral parameters and oscillator strengths of quantum transitions in an active region, which contains cascades of wide quantum wells with a complicated potential profile is developed. A new spatial design of the cascade is calculated and proposed with such an asymmetric arrangement of the wells and barriers, in which, without an applied electric bias, the magnitudes of oscillator strengths are considerable and one-way resonant-tunneling transport of electrons is observed. As a result, it becomes possible to ensure a successful functioning of the broadband photodetector in the far IR range.

An ab initio study on the electronic excited states and photodissociation mechanism of bromocarbene molecule.

We used the internally contracted explicitly correlated multireference configuration interaction (icMRCI-F12) method combined with Davidson correction to conduct a high-precision ab initio study of CHBr. The spin-orbit coupling (SOC) is incorporated into the calculation. The 21 spin-free states split into 53 spin-coupled states of CHBr. The vertical transition energies and oscillator strengths are obtained of these states. The SOC effect on the equilibrium structures and the harmonic vibrational frequencies of the ground state X1A', the lowest triplet state a3A'' and the first excited singlet state A1A'' is investigated. The results reveal a significant effect of the SOC on the bond angle and the frequency of the bending mode of a3A''. The potential energy curves of electronic states of CHBr as functions of the H-C-Br bond angle, C-H bond length, and C-Br bond length, respectively, are also investigated. Based on the calculated results, the interactions between electronic states and photodissociation mechanism involved in CHBr in the ultraviolet region are explored. Our theoretical studies will shed light on the complicated interactions and dynamics of the electronic states of bromocarbenes.

Atomically flat semiconductor nanoplatelets for light-emitting applications.

The last decade has witnessed extensive breakthroughs and significant progress in atomically flat two-dimensional (2D) semiconductor nanoplatelets (NPLs) in terms of synthesis, growth mechanisms, optical and electronic properties and practical applications. Such NPLs have electronic structures similar to those of quantum wells in which excitons are predominantly confined along the vertical direction, while electrons are free to move in the lateral directions, resulting in unique optical properties, such as extremely narrow emission line width, short photoluminescence (PL) lifetime, high gain coefficient, and giant oscillator strength transition (GOST). These unique optical properties make NPLs favorable for high color purity light-emitting applications, in particular in light-emitting diodes (LEDs), backlights for liquid crystal displays (LCDs) and lasers. This review article first introduces the intrinsic characteristics of 2D semiconductor NPLs with atomic flatness. Subsequently, the approaches and mechanisms for the controlled synthesis of atomically flat NPLs are summarized followed by an insight on recent progress in the mediation of core/shell, core/crown and core/crown@shell structures by selective epitaxial growth of passivation layers on different planes of NPLs. Moreover, an overview of the unique optical properties and the associated light-emitting applications is elaborated. Despite great progress in this research field, there are some issues relating to heavy metal elements such as Cd2+ in NPLs, and the ambiguous gain mechanisms of NPLs and others are the main obstacles that prevent NPLs from widespread applications. Therefore, a perspective is included at the end of this review article, in which the current challenges in this stimulating research field are discussed and possible solutions to tackle these challenges are proposed.

State-selective probing of CO2 autoionizing inner valence Rydberg states with attosecond extreme ultraviolet four-wave-mixing spectroscopy

Nonlinear spectroscopies can disentangle spectra that are congested due to inhomogeneous broadening. In conjunction with theoretical calculations, attosecond extreme ultraviolet (XUV) four-wave-mixing (FWM) spectroscopy is utilized here to probe the dynamics of autoionizing inner valence excited Rydberg states of the polyatomic molecule, ${\mathrm{CO}}_{2}$. This tabletop nonlinear technique employs a short attosecond XUV pulse train and two noncollinear, few-cycle near-infrared pulses to generate background-free XUV wave-mixing signals. FWM emission is observed from the $n=5--7$ states of the Henning sharp $nd{\ensuremath{\sigma}}_{g}$ Rydberg series that converges to the ionic $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}\phantom{\rule{4pt}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}_{u}^{+}$ state. However, these transient emission signals decay with lifetimes of 33 $\ifmmode\pm\else\textpm\fi{}$ 6, 53 $\ifmmode\pm\else\textpm\fi{}$ 2, and 94 $\ifmmode\pm\else\textpm\fi{}$ 2 fs, respectively, which calculations show are consistent with the lifetimes of the short-lived $n=6--8$ members of the $ns{\ensuremath{\sigma}}_{g}$ character Henning diffuse Rydberg series. The oscillator strengths of transitions between states involved in all possible resonant FWM processes are calculated, verifying that the nonlinear spectra are dominated by pathways described by an initial excitation to the diffuse $ns{\ensuremath{\sigma}}_{g}$ Rydberg series and emission from the sharp $nd{\ensuremath{\sigma}}_{g}$ Rydberg series. The results substantiate not only that attosecond XUV FWM spectroscopy produces rigorous and meaningful measurements of ultrafast dynamics in polyatomic systems, but also that nonlinear spectroscopic techniques are versatile tools to selectively probe dynamics that are otherwise difficult to access.

The exciton spectrum of the cylindrical quantum dot - quantum ring semiconductor nanostructure in an electric field

In the model of effective masses and rectangular potentials for an electron and a hole, the influence of a uniform electric field on the energy spectrum and wave functions of the exciton and the oscillator strengths of interband quantum transitions in the semiconductor (GaAs/AlxGa1-xAs) quantum dot-quantum ring nanostructure is theoretically investigated. The stationary Schrödinger equations for noninteracting quasiparticles in the presence of an electric field cannot be solved analytically. For their approximate solution, the unknown wave functions are sought in the form of an expansion over the complete set of cylindrically symmetric wave functions, and the electron energy is found by solving the corresponding secular equation. The exciton binding energy is found using perturbation theory.
 The dependences of the energy spectra, the wave functions of an electron, hole, and exciton, and the intensity of interband optical quantum transitions on the magnitude of the electric field strength are analyzed.

Local defects in two-dimensional gallium sulfide as potential single-photon emitters: First-principles evaluation

The single-photon emitters (SPEs) are essential components of emerging quantum communication technology. It has been shown that the local defects in the wide-bandgap semiconductors can be sources of sharp zero-phonon lines (ZPLs) of emission, which is favorable for applications. Most of the reported SPEs emit photons in the visible light region, while fiber-based quantum communication applications require sources of near-infrared (NIR) emission. Therefore, the purpose of this paper is to search for defects which are promising candidates for SPEs in the NIR region by applying computational methods. To this end, based on an educated guess, 12 local doping substitutional defects in two-dimensional (2D) gallium sulfide were selected for consideration. The selected defects are ${Y}_{X}$, where $X=\mathrm{Ga}$ or S, and $Y=\mathrm{C}$, Si, Ge, N, P, As. Here, $X$ stands for a substituted element and $Y$ for a dopant. To evaluate the stability of the defects, their formation energy, binding energy of the dopants, and phonon spectra were calculated within the density functional theory (DFT) approximation. Three defects, ${\mathrm{Ge}}_{\mathrm{Ga}}, {\mathrm{N}}_{\mathrm{Ga}}$, and ${\mathrm{P}}_{\mathrm{Ga}}$, are found to have imaginary-frequency vibration modes, indicating their dynamical instability. They were removed from further consideration. A preliminary analysis of the DFT densities of electronic states (DOS) revealed six remaining defects, ${\mathrm{As}}_{\mathrm{Ga}}, {\mathrm{Ge}}_{\mathrm{S}}, {\mathrm{Si}}_{\mathrm{S}}, {\mathrm{C}}_{\mathrm{S}}, {\mathrm{N}}_{\mathrm{S}}$, and ${\mathrm{P}}_{\mathrm{S}}$, with DOS favorable for formation of local optical excitations in the NIR region. Next, for these six defects, the state-of-the-art linear response GW and the Bethe-Salpeter equation (BSE) methods were used to obtain their electronic structures, in terms of the independent quasiparticle (IQP) states, and optical excitation spectra, in terms of the frequency-dependent dielectric function and the dipole optical transition oscillator strength. The calculation results indicate that the ${\mathrm{C}}_{\mathrm{S}}, {\mathrm{N}}_{\mathrm{S}}$, and ${\mathrm{P}}_{\mathrm{S}}$ defects have intense sharp excitation peaks in the NIR region. The analysis of the contributions of the IQP states to the corresponding BSE eigenstates brings us to the conclusion that these excitations can result in emission with dominating narrow ZPL peaks. I thus propose here the ${\mathrm{C}}_{\mathrm{S}}, {\mathrm{N}}_{\mathrm{S}}$, and ${\mathrm{P}}_{\mathrm{S}}$ defects in 2D GaS as promising candidates for SPEs in the NIR emission region.