Magnetic Dipole Transitions Research Articles

Wavelengths and E1, E2, M1, and M2 line strengths in Nb XXX

The calculations are performed to calculate the excitation energies, wavelengths, line strengths, transition probabilities, and weighted oscillator strengths for the electric-dipole (E1), electric-quadrupole (E2), magnetic-dipole (M1), and magnetic-quadrupole (M2) transitions between the lowest 301 fine-structure levels of the 3snl (n = 3 − 6, l = 0 − 5), 3pnl (n = 3 − 5, l = 0 − 4), and 3dnl (n = 3 − 5, l = 0 − 4) configurations in Mg-like niobium, Nb XXX. In addition, the level designations in the LS- and jj-coupling schemes and lifetimes are presented. The calculations are carried out using the GRASP2018 atomic structure package which is based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) method, with the contributions of the Breit interaction and quantum electrodynamics (QED) corrections included. The accuracy of the present energies, lifetimes, and transition data is calculated utilizing a comparison of the results from the present MCDHF largest layers from two different approaches, as well as the comparison with theoretical and experimental data that are currently accessible.

Study of morphological, elemental, optical and excitation wavelength dependent red photoluminescence in Eu3+ doped Li2SrSiO4 for solid state lighting

A comprehensive investigation of Eu3+ doped Li2SrSiO4 phosphors synthesized via the solid-state reaction method was conducted. XRD confirmed the crystalline phase and SEM along with and its 3D projection's observations confirmed that the phosphor particles were in the micro meter size range, indicating their suitability for applications in primary phosphor-converted LEDs. FTIR spectroscopy elucidated vibrational characteristics, while TGA, EDX and XPS analysed thermal stability, elemental composition and valence states respectively. Doping-induced band gap increase was attributed to the Moss-Burstein effect. Photoluminescence excitation studies revealed enhanced absorption at 394 nm compared to the charge transfer transition band (CTB) at 254 nm, aligning with industry-standard near-ultraviolet chips. XPS suggested two distinct Eu3+ sites in the LSS crystal, corroborated by excitation wavelength-dependent PL emission. As a result of excitation wavelengths, the magnetic-dipole transition (5D0 → 7F1) at 592 nm, the electric-dipole transition (5D0 → 7F2) at 615 nm and the induced electric-dipole transition ((5D0 → 7F3,4) at 650 and 700 nm arose. Additionally, the phosphor gave an improved conversion efficiency at 2% Eu doping. Low synthesis temperature, micro-sized particles, thermal stable, short lifetime, excitation bands at near UV to blue region, colour tunability, lower CCT, LER and similar CIE to available red phosphors are the key factors for the Li2SrSiO4:Eu3+ proving reliable red phosphor for solid state lighting.

Chiral Benzene Triimide (BTI) Radical Anions for Probing the Interplay of Unpaired Electron Spin and Chirality.

Herein a series of chiral BTI radical anions bearing different chiral substituents were efficiently prepared by chemical reduction. X-ray crystallography revealed finely-tuned packing and helix assemblies of the radicals by the size of chiral substituents in crystalline state. In accordance with the crystalline-state packing, the powder ESR spectra indicate that 4 a- ⋅CoCp2 + and 4 c- ⋅CoCp2 + π-dimers exhibit thermally excited triplet states arising from strong spin-spin interactions, while discrete 4 b- ⋅CoCp2 + shows a broad doublet-state signal reflecting weak spin-spin interactions. The interplay between the unpaired electron spin and chiral substituents was studied by UV-Vis-NIR spectra, electronic circular dichroism (ECD) and TD DFT calculations. Different NIR absorptions of the radicals attributing to isolated SOMO→LUMO+1 (~889 nm) transitions were recorded. The emergence of Cotton effects (CEs) at the NIR region for 4 c- ⋅CoCp2 + radical enantiomers suggest the interplay between chirality and unpaired electron spin. The origin of the different circularly polarized light absorptions regarding SOMO derived transitions (around 880 nm) was attributed to chiral substitutes regulated electric and magnetic transition dipole moments of the unpaired electron participated transition.

Refractive index dependence of the radiative rate of a magnetic dipole transition for a nanoparticle system

The emission spectra of Cs2NaEuCl6 nanoparticles (NPs) synthesized by the hot injection method are interpreted. Dispersion of the NPs in alkane solvents experimentally enables the magnetic dipole radiative rate in vacuum for the 5D0 - 7F1 channel to be determined as 14.7 ± 0.1 s−1, in agreement with the calculated value.

The magnetic dipole transition in Rb-like ion and its core-valence correlation effect

This study presents both experimental and theoretical analysis of the 4d2D5/2→2D3/2 magnetic dipole transition in Rb-like ions. Spectral lines of Xe17+, La20+ and Pr22+ ions were recorded using an electron beam ion trap. The theoretical framework employed the fully relativistic Multi-configuration Dirac–Hartree–Fock method, accounting for the Breit interaction, QED effects and comprehensive core-valence correlation. An impressive correlation is observed between the theoretical and experimental findings. Notably, this study illustrates that the contribution of the core-valence correlation, especially concerning deep core subshells, is pivotal for the fine structure splittings.

Fluorescent and electronic properties of Dysprosium acylpyrazolone complexes along with their synthesis and structural features

Six distorted square antiprismatic eight coordinated Dysprosium acylpyrazolone complexes were synthesized having the compositions [Dy(L1)3(EtOH)(H2O)] (DyL1), [Dy(L2)3(EtOH)(H2O)] (DyL2), [Dy(L3)3(EtOH)(H2O)] (DyL3), [Dy(L4)3(EtOH)(H2O)] (DyL4), [Dy(L5)3(EtOH)(H2O)] (DyL5), and [Dy(L6)3(H2O)(EtOH)] (DyL6). The structure of all six complexes was examined using ESI-mass, FT-IR, UV–Vis, powder XRD, and thermogravimetric methods. According to the single crystal analysis of DyL4A, the complex was found eight coordinated (DyO8) with a distorted square antiprismatic geometry. The comparison of stimulated powder pattern of DyL4A crystal and experimental powder x-ray data helps to confirm the geometry of other complexes. In the solid-state emission spectra, the transition 4F9/2→6H13/2, which is close to the yellow region of the visible spectrum (∼510–530 nm), exhibits hypersensitivity. The variance in intensity between electric-dipole and magnetic-dipole transition suggests a less asymmetric environment. The solvent effect has been thoroughly investigated through a comparative analysis of electronic spectra in different solvents. The intensity of emission spectra, Y/B ratio, and antenna effect energy diagram were examined from solid-state emission spectra.

Induced photoelectron circular dichroism onto an achiral chromophore

An achiral chromophore can acquire a chiral spectroscopic signature when interacting with a chiral environment. This so-called induced chirality is documented in electronic or vibrational circular dichroism, which arises from the coupling between electric and magnetic transition dipoles. Here, we demonstrate that a chiroptical response is also induced within the electric dipole approximation by observing the asymmetric scattering of a photoelectron ejected from an achiral chromophore in interaction with a chiral host. In a phenol–methyloxirane complex, removing an electron from an achiral aromatic π orbital localised on the phenol moiety results in an intense and opposite photoelectron circular dichroism (PECD) for the two enantiomeric complexes with (R) and (S) methyloxirane, evidencing the long-range effect (~5 Å) of the scattering chiral potential. This induced chirality has important structural and analytical implications, discussed here in the context of growing interest in laser-based PECD, for in situ, real time enantiomer determination.

Photoluminescence and temperature-dependent luminescence of Ca5(PO4)3OH doped Eu3+ phosphors

In most hosts, the electric dipole transition (EDT) of Eu3+ is usually more intense than the magnetic dipole transition (MDT); however, this is not the case with Ca5(PO4)3OH. Herein, Ca5(PO4)3OH was doped with different Eu3+ concentrations to obtain the maximum emission intensity. The X-ray powder diffraction confirmed that the material crystallised in a single hexagonal Ca5(PO4)3OH phase. The photoluminescence showed two prominent peaks at 573 and 628 nm ascribed to the 5D0-7F1 (MDT) and 5D0-7F2 (EDT) of Eu3+, respectively. The luminescence intensities of the MDT and EDT were comparable when excited with a 305 nm xenon lamp, but when excited with a 325 nm Cd–He laser, the luminescence intensity of the MDT surpassed that of the EDT. The International Commission on Illumination chromaticity coordinates diagram showed that the material emitted a red-orange colour, suggesting it's potential application in red-orange colour displays. The temperature-dependent luminescence was measured, and the relative temperature sensitivities were determined in four different wavelength ranges, suggesting this material's potential application in luminescence thermometry.

Structural, microstructural characterization and luminescence spectroscopy of europium-doped strontium titanate prepared by the sol-gel method

In this work, we report on the polycrystalline Sr1-3x/2EuxTiO3, x = 0.01–0.07 materials prepared by the sol-gel route and their optical properties. The Sr1-3x/2EuxTiO3 powders calcined at 1000 °C showed a microstructure consisting of nanograins with average particle size decreasing from 86.32 nm to 51.87 nm with the increase of Eu amount from 1 at% to 7 at% Eu, as revealed SEM and TEM investigations. Optimized sintering conditions of Eu-doped SrTiO3 ceramics (1400 °C, 4h in air) led to materials with a single phase of cubic SrTiO3. The high purity and uniform distribution of the chemical elements of as-fabricated SrTiO3 doped with Eu guaranteed good optical properties. The emission of the Eu3+ ion mainly occurs for the transitions from the 5D0 level to the levels of the 7Fj (j = 1, 2) term, more precisely, the 5D0 → 7F2 electric dipole transition (∼615 nm) or the 5D0 → 7F1 magnetic dipole transition (∼595 nm). The CIE coordinates of all samples calculated from the emission spectra obtained under the 395 nm and 465 nm excitation wavelength are located in the orange-red region. Therefore, this europium-doped SrTiO3 phosphor is a promising candidate for application as a red-emitting component in solid-state light sources.

Unveiling the force of weak effects in molecular absorption

This work aims at theoretical consideration of weak effects, some of which are well-known in molecular spectroscopy, and some are not yet fully elaborated. A cohesive element of our consideration consists in the use of the original perturbative approach, which significantly facilitates the derivation of the sought expressions and their employment for applications. We consider several examples of perturbative problems concerning permitted or forbidden electric dipole and permitted magnetic-dipole transitions. The suggested approach can be generalized to other effects involving electronic, spin, and higher-order perturbations in molecular spectra.

Observations and identifications of extreme ultraviolet spectra of Ca-like to Na-like neodymium ions using an electron beam ion trap

Abstract Extreme ultraviolet spectra from M-shell transitions in highly-charged Ca-like Nd40+ through Na-like Nd49+ ions were measured at the electron beam ion trap (EBIT) facility of the National Institute of Standards and Technology. To produce the ionization stages of interest, the electron beam energies were varied between 3.60 keV and 10.01 keV. A flat-field grazing incidence spectrometer was used to observe the spectra in the wavelength range between 2.67 nm and 17.30 nm. Simulated spectra generated with detailed collisional-radiative modeling of the non-Maxwellian EBIT plasma were used for line identifications. Forty-seven new spectral lines corresponding to electric-dipole and magnetic-dipole transitions were identified. Measurements were compared to the available previously calculated and predicted values.

Electric field–induced magnetochiral dichroism in a ferroaxial crystal

In a chiral medium, any mirror symmetries are broken, which induces unique physical properties represented by natural optical rotation. When electromagnetic waves propagate through a chiral medium placed in a magnetic field, the refractive index, or equivalently, the absorption encountered by the electromagnetic waves differs depending on whether it travels parallel or antiparallel to the magnetic field. Such a phenomenon is known as magnetochiral dichroism (MChD), which is the characteristic interplay between chirality and magnetism. Similar to chirality, the so-called ferroaxial order, an emergent ferroic state of crystalline materials, is also characterized by mirror symmetry breaking. In contrast to chiral materials, however, the mirror symmetry perpendicular to the crystalline principal axis is allowed in ferroaxial materials. In other words, chirality and thus phenomena unique to chirality can be induced by breaking the remaining mirror symmetry by applying an electric field. Here, we show electric control of chirality and resulting electric field-induced MChD (E-MChD) of the short-wavelength infrared region in a ferroaxial crystal, NiTiO3. We performed spectroscopy measurements of E-MChD by taking a difference of absorption coefficients obtained with and without electric and magnetic fields. As a result, E-MChD was observed around the excitation energy corresponding to Ni2+ d-d magnetic-dipole transitions. The result is nicely explained by adopting the theory of MChD concerning the pseudo-Stark splitting of the energy state. Ferroaxial materials therefore provide platforms to achieve electric control of chirality-related phenomena.

Benchmarking calculations of excitation energies and transition properties with spectroscopic accuracy of highly charged ions used for the fusion plasma and astrophysical plasma

Atomic radiative data such as excitation energies, transition wavelengths, radiative rates, and level lifetimes with high precision are the essential parameters for the abundance analysis, simulation, and diagnostics in fusion and astrophysical plasmas. In this work, we mainly focus on reviewing our two projects performed in the past decade. One is about the ions with Z ≲ 30 that are generally of astrophysical interest, and the other one is about the highly charged krypton (Z = 36) and tungsten (Z = 74) ions that are relevant in research of magnetic confinement fusion. Two different and independent methods, namely, multiconfiguration Dirac–Hartree–Fock (MCDHF) and the relativistic many-body perturbation theory (RMBPT) are usually used in our studies. As a complement/extension to our previous works for highly charged tungsten ions with open M-shell and open N-shell, we also mainly focus on presenting and discussing our complete RMBPT and MCDHF calculations for the excitation energies, wavelengths, electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transition properties, and level lifetimes for the lowest 148 levels belonging to the 3l 3 configurations in Al-like W61+. We also summarize the uncertainties of our systematical theoretical calculations, by cross-checking/validating our datasets from our RMBPT and MCDHF calculations, and by detailed comparisons with available accurate observations and other theoretical calculations. The data are openly available in Science Data Bank at https://doi.org/10.57760/sciencedb.10569.

Chiroptical Properties of Planar Benzobisthiazole-Bridged Squaraine Dimers.

Five chiral squaraine dimers were synthesized by fusing chiral indolenine semisquaraines with three different benzobisthiazole bridges. The thereby created squaraine dimers show a strong splitting of the lowest energy absorption bands caused by exciton coupling. The intensities of the two exciton transitions and the energetic splitting depend on the angle of the two squaraine moieties within the chromophore dimer. The electric circular dichroism spectra of the dimers show intense Cotton effects whose sign depends on the used squaraine chromophores. Sizable anisotropies gabs of up to 2.6 × 10-3 could be obtained. TD-DFT calculations were used to partition the rotational strength into the three Rosenfeld terms where the electric-magnetic coupling turned out to be the dominant contribution while the exciton chirality term is much smaller. This is because the chromophore dimers are essentially planar but the angle between the electric transition dipole moment of one squaraine and the magnetic transition dipole moment of the other squaraine strongly deviates from 90°, which makes the dot product between the two moment vectors and, thus, the rotational strength substantial.

Highly symmetric lattice environment induced orange-red emitting of Eu3+ in a novel tungstate phosphor with broad-band ultraviolet excitation

In this work, we reported the synthesis and characteristic luminescence of an orange-red emitting phosphor NaBa10Y5W4O30: Eu3+ for ultra-violet white light emitting diodes. The phase compound, crystalline structure and morphology are analyzed. The results indicate that a heavy doping of Eu3+ (x = 50%) is realized in NaBa10Y5-5xW4O30: xEu3+ without any impurity phase. Moreover, the optical band gap is analyzed by diffuse reflectance spectroscopy and further confirmed by density function theory (DFT). Meanwhile, the as-synthesized NaBa10Y5W4O30: Eu3+ phosphor can be efficiently pumped by strong broad-band excitation around 315 nm due to the charge transfer transition from [WO6]6- groups to Eu3+. Owing to the highly symmetric lattice environment of Eu3+ in YO6 sites, a strong orange-red emission at 596 nm with color purity of 95.34% is obtained, corresponding to the 5D0→7F1 magnetic dipole transition of Eu3+ ions. The critical concentration is obtained to be x = 15%, and the quenching mechanism is discussed to be dipole–dipole interaction. Furthermore, the temperature dependent emission behavior are analyzed, and the thermal quenching mechanism are explained by the variable temperature decay curve and configuration coordination diagram. Finally, an orange-red light emitting diode lamp is fabricated based on NaBa10Y5W4O30: 15%Eu3+ phosphor and 315 nm semiconductor chip. In summary, the results indicate that NaBa10Y5W4O30: Eu3+ phosphor has the potential to be an orange-red phosphor for white light emitting diodes.

Liquid Crystalline Magneto-Optically Active Peralkylated Azacoronene.

Organic Faraday rotators have gained significant attention in recent years as a promising alternative to traditional inorganic magneto-optical (MO) materials as a result of their lower cost, superior mechanical properties, and potential for large-scale deployment. This interest is peaked by the fact that a number of high symmetry, rigid, strongly optically absorbing organic chromophores display Verdet constants an order of magnitude higher than commercial inorganic Faraday rotators. Critical to the development of new generations of organic materials is the ability to organize them in optimal structures for optical coupling/measurements. We report herein the synthesis of a dodecyl-substituted hexapyrrolohexaazacoronene (C12-HPHAC) displaying discotic liquid crystalline (LC) properties and large Faraday rotation. Thin films with a redox mixed C12-HPHAC/C12-HPHAC+2 composition display a discotic columnar LC phase, are stable to air and moisture in the solid and solution states, and achieve a maximum Verdet constant of 3.36 × 105 deg T-1 m-1 at 700 nm. This result is consistent with Serber's model of magnetic circular birefringence and displays one of the largest reported Verdet constants for organic materials in the UV-Vis range. The LC phase aligns the molecules and leads to gains in Verdet constants of up to 105% through the favorable orientation of the molecules' magnetic and electric transition dipole moments with respect to the applied magnetic field.

Insights into structure, local site symmetry, and energy transfer for regulating luminescent properties of SrLaLiTeO6: Dy/Eu and its application in wLEDs

A series of spectrally tunable Dy3+/Eu3+-coactivated double perovskites SrLaLiTeO6 (SLLT) were synthesized via solid-state ceramic route under air condition. Considering differences of ionic radius and valences among the dopants and host cations, Dy3+/Eu3+ are all inclined to enter La site, though slight occupations in Sr site cannot be completely ruled out. Dy shows narrow band emissions in blue (B) to yellow (Y) region, which is stemmed from magnetic (4F9/2 → 6H15/2) and electric (4F9/2 → 6H13/2) dipole transitions, respectively. Eu3+ exhibits orange-red (O–R) emissions, with two dominant peaks located at ∼ 593 and 617 nm from magnetic (5D0 → 7F1) and electric (5D0 → 7F2) dipole transitions, which could be used as compensation for the red-emitting portion in pc-wLEDs via energy transfer (ET) from Dy to Eu to overcome the disadvantage of low excitation efficiency. The substitutional local site symmetry could be regularly modified along with severely impacting on Y/B and R/O ratios for Dy and Eu emission colors via simply modifying the doping contents, due to changes in bond lengths and Coulomb potentials from interconnected octahedrons [LiO6] and [TeO6] around the dopants. The fabricated pc-wLED via combining a commercial n-UV LED chip with the SLLT: Dy/Eu, exhibited splendid EL performance, with the CIE coordinate is calculated to be (0.3690, 0.3539), CCT of 3232 K, and CRI (Ra) of 86.5. Altogether, it manifests that the stable SLLT: Eu and SLLT: Dy/Eu are potentially good candidates for applications as red and white phosphors, respectively in indoor plant growth LED and pc-wLEDs.

Calculations of multipole transitions in Sn II for kilonova analysis

We use the method that combines linearized coupled-cluster and configuration interaction approaches for calculating energy levels and multipole transition probabilities in singly ionized tin ions. We show that our calculated energies agree very well with the experimental data. We present probabilities of magnetic dipole and electric quadrupole transitions and use them for the analysis of the AT2017gfo kilonova emission spectra. This study demonstrates the importance and utility of accurate atomic data for forbidden transitions in the examination of future kilonova events.Graphical abstract

Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance.

Photochemical reaction exploiting an excited triplet state (T1 ) of a molecule requires two steps for the excitation, i.e., electronic transition from the ground (S0 ) to singlet excited (S1 ) states and intersystem crossing to the T1 state. A dielectric metasurface coupled with photosensitizer that enables energy efficient photochemical reaction via the enhanced S0 →T1 magnetic dipole transition is developed. In the direct S0 →T1 transition, the photon energy of several hundreds of meV is saved compared to the conventional S0 → S1 →T1 transition. To maximize the magnetic field intensity on the surface, a silicon (Si) nanodisk array metasurface with toroidal dipole resonances is designed. The surface of the metasurface is functionalized with ruthenium (Ru(II)) complexes that work as a photosensitizer for singlet oxygen generation. In the coupled system, the rate of the direct S0 →T1 transition of Ru(II) complexes is 41-fold enhanced at the toroidal dipole resonance of a Si nanodisk array. The enhancement of a singlet oxygen generation rate is observed when the toroidal dipole resonance of a Si nanodisk array is matched with the direct S0 →T1 transition wavelength of Ru(II) complexes.

One-dimensional LaF3:RE3+ (RE=Eu, Nd) nanostructured phosphors: Controllable synthesis and luminescence properties

A novel and universal method combining electrospinning with a twi-crucible fluorinating technology was utilized to fabricate one-dimensional LaF3:RE3+ (RE = Eu, Nd) nanostructured phosphors. A series of nanofibrous/nanoribbon-shaped LaF3:RE3+ (RE = Eu, Nd) phosphors were devised and facilely fabricated through the calcination of the relevant nanofibrous/nanoribbon-shaped La2O3:RE3+ (RE = Eu, Nd) precursors in air by applying a twi-crucible fluorinating method utilizing NH4HF2 as a fluorine source without additional usage of reducing gas and protective gas. Nanofibrous/nanoribbon-shaped La2O3:RE3+ (RE = Eu, Nd) precursors were synthesized by calcinating the electrospun nanofibrous/nanoribbon-shaped [RE(NO3)3+La(NO3)3]/polyvinyl pyrrolidone (PVP) composites. Nanofibrous/nanoribbon-shaped LaF3:RE3+ (RE = Eu, Nd) phosphors possess hexagonal structures with a space group of P63/mmc. Nanofibrous LaF3:RE3+ (RE = Eu, Nd) phosphors present excellent fibrous morphology with a uniform diameter of 131–143 nm. Nanoribbon-shaped LaF3:Eu3+ phosphors with 94.5 nm in thickness and 5.1 ± 0.4 μm in width were acquired. Nanoribbon-shaped LaF3:Nd3+ phosphors have a thickness of 179 nm and a width of 4.2 ± 0.4 μm. Upon excitation by ultraviolet light at 396 nm, nanofibrous/nanoribbon-shaped LaF3:Eu3+ phosphors emit the main emission band at approximately 591 nm, corresponding to the 5D0→7F1 magnetic dipole transition of Eu3+. With an increment of Eu3+ concentration, the fluorescent strength of nanofibrous LaF3:Eu3+ phosphors is improved greatly and achieves a maximum when the Eu3+ concentration is approximately 5 mol%. Moreover, the nanofiber/nanoribbon-shaped LaF3:Eu3+ phosphors emit a yellow color. For Nd3+-doped phosphors, nanofibrous/nanoribbon-shaped LaF3:Nd3+ phosphors possess near-infrared optical performances, and the main emission peak is at 854 nm, corresponding to the 4F3/2 → 4I9/2 transition of Nd3+. The luminescence intensity of LaF3:Nd3+ phosphors decreases significantly with increasing Nd3+ content and reaches a maximum at 5 mol% Nd3+. The corresponding formative mechanisms of nanofibrous/nanoribbon-shaped RE3+ (RE = Eu, Nd) phosphors are expounded, and the corresponding construction technique is established. The new findings in this work lay a foundation for wide applications of rare earth fluoride one-dimensional nanostructures.