Electric Dipole Transition Research Articles

Quadrupole Effects in the Photoionisation of Sodium 3s in the Vicinity of the Dipole Cooper Minimum

A procedure to obtain relativistic expressions for photoionisation angular distribution parameters using the helicity formulation is discussed for open-shell atoms. Electric dipole and quadrupole transition matrix elements were considered in the present work, to study the photoionisation dynamics of the 3s electron of the sodium atom in the vicinity of the dipole Cooper minimum. We studied dipole–quadrupole interference effects on the photoelectron angular distribution in the region of the dipole Cooper minimum. Interference with quadrupole transitions was found to alter the photoelectron angular distribution, even at rather low photon energies. The initial ground and final ionised state discrete wavefunctions of the atom were obtained in the present work using GRASP, and we employed RATIP with discrete wavefunctions, to construct continuum wavefunctions and to calculate transition amplitudes, total cross-sections and angular distribution asymmetry parameters.

Corrosion resistance of fluorescent carbon fiber reinforced FEVE and fluorescence detection of coating surface

Fluorocarbon resin coating plays a significant role in marine severe corrosion protection. However, seawater has a great influence on the corrosion rate of materials, so it is necessary to strengthen the monitor of marine materials during service. In this study, using solvothermal method, the rare earth (RE) europium nitrate, 1.10-phenoline and concentrated nitric acid oxidized carbon fiber (CF) were chemically doped in the reactor to prepare a kind of carbon fiber with fluorescent characteristics. Then, the RE modified CF was mechanically mixed with fluorocarbon resin to prepare a fluorescent indicator anti-corrosive coating with intrinsic red light emission guided by Eu3+ ultra-sensitive electric dipole transition (5D0→7F2). The correlation between corrosion time and fluorescence spectroscopy could be established to detect the corrosion resistance of the coating, it provides a reference for the anti-corrosion intelligent indication of the coating.

Unidirectional Meta-Emitters Based on the Kerker Condition Assembled by DNA Origami.

Optical quantum emitters near nanostructures have access to additional relaxation channels and thus exhibit structure-dependent emission properties, including quantum yield and emission directionality. A well-engineered quantum emitter-plasmonic nanostructure hybrid can be considered as an optical meta-emitter consisting of a transmitting nanoantenna driven by an optical-frequency generator. In this work, the DNA origami fabrication method is used to construct ultracompact unidirectional meta-emitters composed of a plasmonic trimer nanoantenna driven by a single dye molecule. The origami is designed to bring the dye to the gap to simultaneously excite the electric and magnetic dipole modes of the trimer nanoantenna. The interference of these modes fulfills the Kerker condition at the fluorophore's emission band, enabling unidirectional emission. We report unidirectional emission from a single molecule with a front-to-back ratio of up to 10.7 dB accompanied by a maximum emission enhancement of 23-fold.

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.

A novel narrow-band red-emitting multi-layer phosphor for white – Light emitting devices

SrZr2La2O7: Eu+3 (0.5–2.5 mol %) phosphors have been synthesized through the standard solid-state reaction technique. The photoluminescent and other structural properties such as PXRD (Powder X-ray Diffraction), SEM (Scanning Electron Microscopy) and Energy Dispersive X-ray spectroscopy (EDX), FTIR (Fourier transform infrared spectroscopy), PSD (Particle Size Distribution) of the phosphors were learned. The photoluminescence spectra show that the phosphor exhibited intense and dominant red emissions at 627 nm belonging to the 5D0 → 7F2 electric dipole transition. The FWHM of the red emissions at 627 nm is only 8.0 nm increasing in luminous efficacy. Hereby we propose a novel RED phosphor for RED emitting LEDs with phosphor-embedded polymer matrix layers of variable thickness and stacking up to 400 µm. The intensity of the red color was enhanced by self-excitation of photon absorption and emission. As a result, Eu3+doped SrZr2La2O7 phosphors can be widely used as red phosphors in UV chip-based WLEDs and displays. The phosphor exhibits high color purity up to 99% when excited at 590 nm. X-ray powder diffraction analysis confirms that the phosphor is highly crystalline and has a cubic phase.

Dynamic control of light scattering in a single particle enabled by time modulation

The interaction of light with time-varying materials offers intriguing opportunities for controlling light scattering and wavefront manipulation, thereby unlocking fascinating applications in the realm of optics and photonics. In this study, we present an analytical solution for the scattering from a particle made of a material with time-varying permittivity by exploiting the T-matrix approach. Through the manipulation of the active medium's eigenvalues, we demonstrate the pivotal ability to regulate the elements of a dynamically controlled T-matrix, thus enabling precise control over the scattering characteristics of the particle. Crucially, this dynamic control is achieved without resorting to modifying the particle's inherent physical parameters, such as shape, size, and dispersion. We demonstrate that the eigenvalues of the dynamic material can be skillfully manipulated through the adequate choice of the particle's modulation function, resulting in either in-phase or out-of-phase interactions between the magnetic and electric dipole modes, allowing us to satisfy the Kerker conditions at diverse harmonics. The results of the optimal modulation functions are presented in both the near-field and far-field regions, revealing time modulation as a dynamic means of achieving unidirectional scattering. Our findings pave the way for developing time-varying structures comprising dynamic meta-atoms, offering valuable insight into advanced light–matter interactions, and providing lucrative guidance for future research in the realm of dynamic photonic systems.

Revealing Mie Resonances with Enhanced and Suppressed Second‐Order Nonlinear Optical Responses in a Hexagonal‐Prism‐Like MoS2 Nanoparticle

AbstractTransition metal dichalcogenides (TMDC), such as molybdenum disulfide (MoS2), have attracted great interest owing to their excellent electronic and optical properties. Efficient second harmonic generation (SHG) has been successfully demonstrated in the MoS2 monolayer, in sharp contrast to the negligible SHG from the bulk material. Here, the nonlinear optical responses of hexagonal‐prism‐like MoS2 nanoparticles are investigated, which support Mie resonances in the near infrared spectral range. It is revealed that the Mie resonances of such a MoS2 nanoparticle can be clarified into two types, which exhibit enhanced and suppressed SHG. It is verified that the SHG from the MoS2 nanoparticle is strongly correlated with the electric field distribution at the optical resonance. For the electric quadrupole mode with an anti‐symmetric electric field distribution, the SHG is greatly suppressed. As a result, a nanohole appears in the emission pattern of the SHG from the MoS2 nanoparticle. In sharp contrast, the SHG from the electric dipole mode with a symmetric electric field distribution can be one order of magnitude stronger than that from a MoS2 monolayer. The findings open new horizons for manipulating the nonlinear optical responses of TMDC nanoparticles and pave the way for realizing photonic devices.

Semi-empirical evaluation of isospin mixing from forbidden E1 transitions

ΔT = 0 electric dipole transitions in self conjugate nuclei, forbidden by isospin selection rules, are readily seen in nature. This implies that the states participating in these transitions may not be of pure isospin T. This work identifies some of these transitions in a few upper-sd shell self-conjugate nuclei and attempts to calculate the degree of isospin mixing in these nuclei by using the standard two-level mixing formalism in a semi-empirical approach. The physically observed E1 transitions are broken down into two theoretically allowed ΔT = 1 channels. These allowed components have been calculated within the shell model. Our results are consistent with both theoretical and experimental values found in the literature.

Vortex beam generator based on exceptional topological phase in terahertz all-dielectric metasurface

In this study, an all-dielectric metasurface with an F-shaped chiral structure in the terahertz region has been proposed. The coupling between the electric and magnetic dipole modes supported by the metasurface can be adjusted by varying the structural parameters. In the parameter space composed of l l and s, any closed path around exceptional point in the circular polarization conversion channel t rl generates a topologically protected exceptional topological phase. A vortex beam generator with a unit topological charge was proposed to provide a novel concept for designing terahertz metasurface wavefront modulation devices.

Magnetic Mode Coupling in Hyperbolic Bowtie Meta-Antennas.

Hyperbolic metaparticles have emerged as the next step in metamaterial applications, providing tunable electromagnetic properties on demand. However, coupling of optical modes in hyperbolic meta-antennas has not been explored. Here, we present in detail the magnetic and electric dipolar modes supported by a hyperbolic bowtie meta-antenna and clearly demonstrate the existence of two magnetic coupling regimes in such hyperbolic systems. The coupling nature is shown to depend on the interplay of the magnetic dipole moments, controlled by the meta-antenna effective permittivity and nanogap size. In parallel, the meta-antenna effective permittivity offers fine control over the electrical field spatial distribution. Our work highlights new coupling mechanisms between hyperbolic systems that have not been reported before, with a detailed study of the magnetic coupling nature, as a function of the structural parameters of the hyperbolic meta-antenna, which opens the route toward a range of applications from magnetic nanolight sources to chiral quantum optics and quantum interfaces.

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.

Bound states in the continuum driven by multiple modes for high Q refractive index sensing in metasurfaces

Bound states in the continuum (BICs) have attracted much attention in the field of refractive index sensing. In this paper, we propose multi-mode symmetry-protected BICs (SP-BICs) and the Freidrich–Wintgen BIC (FW-BIC) in terahertz metasurfaces consisted of periodic open split ring resonators. Firstly, multi-mode SP-BICs are subject to the magnetic dipole, electric dipole (ED), and toroidal dipole (TD) modes. Moreover, we demonstrate the FW-BIC by strongly coupling the electric quadrupole and TD modes. For micron film sensing of the ED mode, simulation results show that the Q factor, the sensitivity of sensing (S), and the corresponding figure of merit can simultaneously reach 1561, 141 GHz/RIU, and 306, respectively. Our quasi-BICs have potential applications in micro-sensing.

Influence of Ga Substitution on the Local Structure and Luminescent Properties of Eu-Doped CaYAlO4 Phosphors

Understanding the local environment of luminescent centers in phosphors serves as a blueprint for designing the luminescent properties of phosphors. Chemical substitution is a general strategy for engineering the local structure around luminescent center ions. In this study, we systematically investigate the luminescent properties of Ga-substituted Eu-doped CaYAlO4 (CYAGO:Eu) phosphors and the local structure of the Eu ions. The Ga substitution at the Al sites leads to a significant enhancement in the electric dipole transition of Eu3+ (5D0 → 7F2). The Judd–Ofelt analysis reveals that Eu3+ ions are substituted for Ca/Y, and the Ga substitution increases the asymmetricity of the local structure around the Eu ions because of the different ionic radii and electronegativities of Al and Ga. In addition, Eu2+ emission is missing regardless of the Ga substitution and post-hydrogen treatments. The present work provides deeper insight into the role of chemical substitution in oxide phosphors.

Tailing Optical Pulling Force on a Metal-Dielectric Hybrid Dimer with Electromagnetic Coupling.

In this work, we demonstrate that optical pulling forces (OPFs) can be induced by a hybrid dimer consisting of a Si nanoparticle (NP) and a coated nanoparticle with a gain core and Au shell under normal plane wave illumination. Analytical theory reveals that the underlying physical mechanism relies on interactions between the electric dipole (ED) modes excited in the NPs. As compared with the individual NP, it is found that the magnitude of optical force can be enlarged by almost three orders for the Si NP and one order for the coated gain NP in the coupled dimer. In addition, we find that the OPFs exerted on the NPs are heavily dependent on the gain level of the core materials, the incident polarization angle and the sizes of the NPs. More interestingly, we find that the OPF can also be exerted on a trimer system consisting of two identical Si NPs and a coated NP arranged in a line. The related results could be used to propose a versatile platform for manipulating NPs.

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.

Freestanding, Freeform Metamolecule Fibers Tailoring Artificial Optical Magnetism.

Metamolecule clusters support various unique types of artificial electromagnetism at optical frequencies. However, the technological challenges regarding the freeform fabrication of freestanding metamolecule clusters with programmed geometries and multiple compositions remain unresolved. Here, the freeform, freestanding raspberry-like metamolecule (RMM) fibers based on the directional guidance of a femtoliter meniscus are presented, resulting in the evaporative co-assembly of silica nanoparticles and gold nanoparticles with the aid of 3D nanoprinting. This method offers a facile and universal pathway to shape RMM fibers in 3D, enabling versatile manipulation of near- and far-field characteristics. In particular, the authors demonstrate the ability to decrease the scattering of the millimeter-scale RMM fiber in visible spectrum. In addition, the influence of electric and magnetic dipole modes on the directional scattering of RMM fibers is investigated. These experiments show that the magnetic response of an individual RMM can be controlled by adjusting the filling factor of gold nanoparticles. The authors anticipate that this method will allow for unrestricted design and realization of nanophotonic structures, surpassing the limitations of conventional fabrication processes.

Photoluminescence Anisotropy in Eutectic Crystals of Polynuclear Lanthanide Complexes and Silver Clusters

AbstractAnisotropy is an intrinsic property of crystalline materials. However, the photoluminescence anisotropy in eutectic crystals of organometallic complexes has remained unexplored. Herein, the eutectic of polynuclear lanthanide complexes and Ag clusters was prepared, and the crystal shows significant photoluminescence anisotropy. The polarization anisotropy of emission δ and degree of excitation polarization P are 2.62 and 0.53, respectively. The rare excitation polarization properties have been proved to be related to the regular arrangement of electric transition dipole moments of luminescent molecules in the crystal. Our design provides a reference for developing new photoluminescence anisotropy materials and expanding their applications.

Photoluminescence Anisotropy in Eutectic Crystals of Polynuclear Lanthanide Complexes and Silver Clusters.

Anisotropy is an intrinsic property of crystalline materials. However, the photoluminescence anisotropy in eutectic crystals of organometallic complexes has remained unexplored. Herein, the eutectic of polynuclear lanthanide complexes and Ag clusters was prepared, and the crystal shows significant photoluminescence anisotropy. The polarization anisotropy of emission δ and degree of excitation polarization P are 2.62 and 0.53, respectively. The rare excitation polarization properties have been proved to be related to the regular arrangement of electric transition dipole moments of luminescent molecules in the crystal. Our design provides a reference for developing new photoluminescence anisotropy materials and expanding their applications.

Opacities of singly and doubly ionized neodymium and uranium for kilonova emission modeling

ABSTRACT Even though the electromagnetic counterpart AT2017gfo to the binary neutron star merger GW170817 is powered by the radioactive decay of r-process nuclei, only few tentative identifications of light r-process elements have been made so far. One of the major limitations for the identification of heavy nuclei is incomplete or missing atomic data. While substantial progress has been made on lanthanide atomic data over the last few years, for actinides there has been less emphasis, with the first complete set of opacity data only recently published. We perform atomic structure calculations of neodymium (Z = 60) as well as the corresponding actinide uranium (Z = 92). Using two different codes [flexible atomic code (fac) and hartree–fock-relativistic (hfr)] for the calculation of the atomic data, we investigate the accuracy of the calculated data (energy levels and electric dipole transitions) and their effect on kilonova opacities. For the fac calculations, we optimize the local central potential and the number of included configurations and use a dedicated calibration technique to improve the agreement between theoretical and available experimental atomic energy levels (AELs). For ions with vast amounts of experimental data available, the presented opacities agree quite well with previous estimations. On the other hand, the optimization and calibration method cannot be used for ions with only few available AELs. For these cases, where no experimental nor benchmarked calculations are available, a large spread in the opacities estimated from the atomic data obtained with the various atomic structure codes is observed. We find that the opacity of uranium is almost double the neodymium opacity.