Electric Dipole Transition Research Articles

Synthesis, Photoluminescent Characteristics and Eu3+-Induced Phase Transitions in Sr3Zr2O7:Eu3+ Red Phosphors.

Designing phosphors that are excited by blue light is extraordinarily important for white light-emitting diodes (w-LEDs). In the present study, a new Ruddlesden-Popper type of SZO:xEu3+ (x = 0.01~0.10) phosphors was developed using solid-state reactions. Interestingly, a Eu3+ doping-induced phase transformation from the Sr3Zr2O7 (cubic) to the SrZrO3 (orthorhombic) phase was observed, and the impact of the occupied sites of Eu3+ ions on the lifetime of Sr3Zr2O7:xEu3+ phosphors is discussed in detail. Diffuse reflectance spectroscopy results showed that the band gap of SZO:xEu3+ phosphors gradually increased from 3.48 eV for undoped Sr3Zr2O7 hosts to 3.67 eV for SZO:0.10Eu3+ samples. The fluorescence excitation spectrum showed that ultraviolet (300 nm), near-ultraviolet (396 nm) and blue light (464 nm) were all effective excitation pump sources of Sr3Zr2O7:xEu3+ phosphors, and the strongest emission at 615 nm originated from an electric dipole transition (5D0→7F2). CIE coordinates moved from orange (0.5969, 0.4267) to the reddish-orange region (0.6155, 0.3827), and the color purity also increased. The fabricated w-LED was placed on a 460 nm chip with a mixture of YAG:Ce3+ and SZO:0.1Eu3+ samples and showed "warm" white light with a color rendering index (CRI) of 81.8 and a correlation color temperature (CCT) of 5386 K, indicating great potential for application in blue chip white LEDs.

НОВЫЕ ДАННЫЕ ОБ ОСОБЕННОСТЯХ ЛОКАЛЬНОЙ СТРУКТУРЫ ТВЕРДОГО РАСТВОРА Ca9La(PO4)7(1-x)(VO4)7x:Eu3+(1 %)

Solid solutions of phosphate-vanadates Ca9La(PO4)7(1–x)(VO4)7x:Eu3+(1 %) with the structure -Ca3(PO4)2 activated by europium were synthesized by the standard solid-phase method. It is shown that a continuous series of solid solutions is formed upon substitution P5+ → V5+. At the same time, the study by the second harmonic generation method showed that a symmetry inhomogeneity is observed in the series. When studying the luminescent properties, standard transitions of the europium cation with the dominant electric dipole transition 5D0 → 7F2 were found. The most intense emission was demonstrated by compositions with a centrosymmetric structure.

Annular and unidirectional transverse scattering with high directivity based on magnetoelectric coupling.

Transverse scattering is a special directional scattering perpendicular to the propagation direction, which has attracted great interest due to its potential applications from directional antennas, optical metrology to optical sensing. Here we reveal annular transverse scattering and unidirectional transverse scattering by magnetoelectric coupling of Omega particle. The annular transverse scattering can be achieved by the longitudinal dipole mode of the Omega particle. Furthermore, we demonstrate the highly asymmetric unidirectional transverse scattering by adjusting the transverse electric dipole (ED) and longitudinal magnetic dipole (MD) modes. Meanwhile, the forward scattering and backward scattering are suppressed by the interference of transverse ED and longitudinal MD modes. In particular, the lateral force exerted on the particle is accompanied by the transverse scattering. Our results provide a useful toolset for manipulating light scattered by the particle and broaden the application range of the particle with magnetoelectric coupling.

Frequency measurement of 6s6p 3P0,2−6s7s 3S1 transitions in ultracold 171Yb atoms referenced to local optical clock

We experimentally determine the absolute frequencies and hyperfine splittings of the 6s6p3P0,2 − 6s7s3S1 transitions of ultracold 171Yb atoms in an optical lattice. A frequency comb referenced to an ultrastable optical cavity is used to measure the electric-dipole transition frequencies. With the normalized shelving detection technique, about 12 MHz and 10 MHz linewidth of atomic spectra are obtained, respectively, which is some greater than the natural linewidth of 1.5 MHz and 5.9 MHz and is limited by the broadening from the probe and lattice light. By reference to our 171Yb 6 s2 1S0 − 6s6p3P0 clock, the absolute frequencies are found to be 461861338.03 (0.21) MHz and 461871596.07 (0.31) MHz for the 6s6p3P0 − 6s7s3S1 (F = 1/2 and F = 3/2) transitions, which are more accurate than the previous measurement by one order of magnitude. For the 6s6p3P2 (F = 3/2 and F = 5/2) − 6s7s3S1 (F = 1/2 and F = 3/2) transitions, the measured frequencies are 389257019.71 (0.65) MHz, 389267277.10 (0.37) MHz and 389260569.95 (0.89) MHz, respectively, which are the first measurements to our knowledge. Furthermore, the hyperfine constants for the 6s6p3P2 and 6s7s3S1 states are determined to be 2682.86(0.38) MHz and 6838.69(0.25) MHz, both of which agree well with other recent experimental results.

Hamiltonian sensitivity in calculating the electromagnetic moments and electroexcitation form factor for the sd nuclei using shell model with Skyrme–Hartree–Fock

In this work, the nuclear electromagnetic moments for the ground and low-lying excited states for sd shell nuclei have been calculated, resulting in a revised database with 56 magnetic dipole moments and 41 electric quadrupole moments. The shell model calculations are performed for each sd isotope chain, considering the sensitivity of changing the sd two-body effective interactions USDA, USDE, CWH and HBMUSD in the calculation of the one-body transition density matrix elements. The calculations incorporate the single-particle wave functions of the Skyrme interaction to generate a one-body potential in Hartree–Fock theory to calculate the single-particle matrix elements. For most sd shell nuclei, the experimental data are well reproduced, except for those spans near the island of inversion. In order to interpret the structure of low-lying excited states, the electric quadrupole and magnetic dipole transition form factors and the corresponding reduced transition probabilities in the sd shell nuclei have also been calculated, for which the experimental data are available. The present results demonstrate the nuclear electromagnetic moments’ sensitivity to many forms of the understanding of nucleon–nucleon interactions and provide a crucial baseline for future improvements in conceptual calculations.

Synthesis, characterization, and exploring optical pathways of centrosymmetric Li2MgP2O7/ZnMgP2O7: Eu3+pyrophosphate phosphor for LEDs applications

The present study reports the synthesis of two new centrosymmetric pyrophosphates Li2MgP2O7:Eu3+and ZnMgP2O7:Eu3+compounds by the wet-chemical method. Structural confirmation and phase purity were primarily investigated by XRD analysis and FT-IR. Li2MgP2O7:Eu3+ belongs to the P21/m space group of the monoclinic crystal system, while ZnMgP2O7:Eu3+ phosphor crystallizes in a monoclinic system with a P21/n space group. Herein, these compounds exhibit strong optical absorption over a wavelength range of 200–800 nm. Photoluminescence emission spectra (PL) interestingly reveal their structural elucidation and optical trait to uncover their commercial applications. At 362 nm excitation, a series of emission bands were recorded at different regions. The dominant greenish emission peak was found at 548 nm. We have also recorded another emission peak at 598 nm, 612 nm, and 617 nm, which were much weaker than the former profile peak. The peak at 598 nm is attributed due to 5D0 -7F1 electric dipole transitions. Whereas, the peak at 617 nm belongs to the forbidden f-f transitions, ascribed due to 5D0 -7F2. The CIE chromaticity coordinates explains the nature of the color bands of phosphors based on their particular wavelengths. The Judd-Ofelt (J–O) strongly suggested that the prepared phosphors will act as a potential candidate for the fabrication of illuminating devices and the construction of w-LEDs.

Studying optical properties of Gd<sub>2</sub>O<sub>3</sub>:Eu nanophosphor by Judd-Ofelt theory

Eu3+doped Gd2O3 nanophosphor were successfully obtained by a straightforward combustion method. The crystal structure and optical characteristics were investigated by methods: XRD, photoluminescence spectra (PL). The XRD result indicates the Gd2O3:5%Eu had cubic phase and the average particle size was about 32 nm. The photoluminescence showed the strong red emission with the 5D0-7F2 electric dipole transition was dominant. The intensities of 5D0-7FJ transitions depended on the symmetry of the local environment of Eu3+ ions and were described using the Judd–Ofelt analysis, using Ω2 and Ω4 intensity parameters derived from emission spectra data analysis. The calculated lifetime value was 1.8 ms and the quantum efficiency was 58,63%.

Crystal structure and photoluminescence properties of CaLaLiTeO6:Dy3+ phosphors for solid-state lighting

A series of CaLa1-xLiTeO6:xDy3+ phosphors were synthesized via a conventional solid-state reaction method, and the effects of different Dy3+ doping concentrations on the luminescence properties of the phosphors were studied. The excitation spectrum indicated that these synthesized phosphors had strong absorption bands in near-ultraviolet (n-UV) region in the range from 300 to 500 nm. There were two sharp emission peaks in the visible region, which were located at 483 nm, 574 nm, corresponding to transitions of 4F9/2→6H15/2 (magnetic dipole transition) and 4F9/2→6H13/2 (electric dipole transition), respectively. The phosphor CaLa0.95LiTeO6:0.05Dy3+ shows superior thermal stability. When the temperature rises to 425 K, the luminous intensity remains at 79% compared with the initial intensity of 300 K. These results demonstrate that the CaLa1-xLiTeO6:xDy3+ phosphors have great potential as a single-phase luminescence material for near-ultraviolet (n-UV) excitation.

Microwave-assisted synthesis and thermally stable red fluorescence of Ba3(ZnB5O10)PO4:Eu3+ solid solution

Red-emitting materials play a significant role in phosphor-converted white light-emitting diodes (WLEDs), since it can effectively improve the chromatic properties of the solid-state lighting source. In this work, we employ a microwave-assisted solid-state reaction to prepare a red-emitting Ba3(ZnB5O10)PO4:Eu3+ (BZBP:Eu3+) phosphor. Eu3+ activators are solidly dissolved into the BZBP host via occupying the Ba2+ positions. Excited by 395 ​nm, the title phosphor yields red emission with high color purity, which is dominated by the electric dipole transition of Eu3+. Base on the investigation of photoluminescence in response to the Eu3+ content, the content quenching mechanism is understood. Besides, the study on the luminescence temperature quenching reveals the good thermal stability and resistance to chromaticity shifting. The results indicate that the studied phosphor would be an alternative red-emitting material for WLEDs.

Fabrication and in vitro characterization of antibacterial magneto-luminescent core-shell bioactive glass nanoparticles

When nanomaterials with antibacterial properties were sent to the infected area, it was predicted that infection and related complications could be prevented. The nanoparticles can be designed to possess magnetic and luminescence (magneto-luminescent) properties to be effectively targeted and localized at the infection foci without dispersing into the body. Simultaneously, the magneto-luminescent characteristic of particles allows visualization and confirmation of localized particles at the desired area. In this regard, there are no studies on the use of antibacterial magneto-luminescent bioactive glass for orthopedic applications and the treatment of orthopedic device-related infections. In this study, antibacterial magneto-luminescent 58S bioactive glasses were synthesized by the modified Stöber using coupled with a layer-by-layer assembly approach to possess core/shell particle morphology. SPION/Bioactive glass nanoparticles had an average size of 50 nm and displayed superparamagnetic behavior. While the saturation magnetization value (σs) of the undoped 58S sample was 25.32 emu/g, that of the co-doped sample (2% Eu, 2% Zn) was 21.74 emu/g; this showed that the doping slightly reduced the magnetization value. Europium (Eu) doping of SPION/Bioactive glass nanoparticles induced characteristic red emission originating from Eu emissions belonging to 5D0–7FJ (J = 1–4) transitions and the strongest peak was at 612 nm (electric-dipole transition, 5D0–7F2). Color chromaticity coordinates confirmed emission in the red region. XPS spectrum revealed the existence of Eu and Zn dopant elements in 58S bioactive glass. After soaking characteristic peaks at 31.74° and 45.43° belonging to the hexagonal hydroxyapatite phase were detected in the XRD data, confirming the SEM images. 2% Eu doped SPION/Bioactive glass nanoparticles had the highest osteoblast viability up to 7 days in vitro, while doping the samples with 2% zinc did not yield bone cell viability as high as the Eu doped ones. Importantly, Eu doped SPION/Bioactive glass nanoparticles inhibited gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) growth up to 48 h in vitro. The results showed that Eu doping of SPION/Bioactive glass nanoparticles increased osteoblast viability and inhibited bacterial growth, while possessing superparamagnetic properties and exhibiting red luminescence.

Spin polarization through axially chiral linkers: Length dependence and correlation with the dissymmetry factor.

The chiral-induced spin selectivity (CISS) effect relates to the spin-selective electron transport through chiral molecules; therefore, the chiral molecules act as spin filters. In past studies, correlation was found between the magnitude of the spin filtering and the intensity of the circular dichroism (CD) spectrum (the first Compton peak) of the molecules. Since the intensity of the CD peak relates to both the magnitude of the electric and magnetic dipole transitions, it was not clear which of these properties correlate with the CISS effect. This work aims at addressing this question. By studying the spin-dependent conduction and the CD spectra of the thiol-functionalized enantiopure binaphthalene (BINAP) and ternaphthalene (TERNAP), we found that both BINAP and TERNAP exhibit a similar spin polarization of 50%, despite the first Compton peak in TERNAP being almost twice as intense as the peak in BINAP. These results can be explained by the similar values of their anisotropy (or dissymmetry) factor, gabs , which is proportional to the magnetic transition dipole moment. Hence, we concluded that the CISS effect is proportional to the transition dipole moment in chiral molecules, namely, to the dissymmetry factor.

Highly Strained Oxygen‐Doped Chiral Molecular Belts of the Zigzag‐Type with Strong Circularly Polarized Luminescence

AbstractHerein we report a two‐directional cyclization strategy for the synthesis of highly strained depth‐expanded oxygen‐doped chiral molecular belts of the zigzag‐type. From the easily accessible resorcin[4]arenes, an unprecedented cyclization cascade generating fused 2,3‐dihydro‐1H‐phenalenes has been developed to access expanded molecular belts. Stitching up the fjords through intramolecular nucleophilic aromatic substitution and ring‐closing olefin metathesis reactions furnished a highly strained O‐doped C2‐symmetric belt. The enantiomers of the acquired compounds exhibited excellent chiroptical properties. The calculated parallelly aligned electric (μ) and magnetic (m) transition dipole moments are translated to the high dissymmetry factor (|glum| up to 0.022). This study provides not only an appealing and useful strategy for the synthesis of strained molecular belts but also a new paradigm for the fabrication of belt‐derived chiroptical materials with high CPL activities.

Highly Strained Oxygen-Doped Chiral Molecular Belts of the Zigzag-Type with Strong Circularly Polarized Luminescence.

Herein we report a two-directional cyclization strategy for the synthesis of highly strained depth-expanded oxygen-doped chiral molecular belts of the zigzag-type. From the easily accessible resorcin[4]arenes, an unprecedented cyclization cascade generating fused 2,3-dihydro-1H-phenalenes has been developed to access expanded molecular belts. Stitching up the fjords through intramolecular nucleophilic aromatic substitution and ring-closing olefin metathesis reactions furnished a highly strained O-doped C2 -symmetric belt. The enantiomers of the acquired compounds exhibited excellent chiroptical properties. The calculated parallelly aligned electric (μ) and magnetic (m) transition dipole moments are translated to the high dissymmetry factor (|glum | up to 0.022). This study provides not only an appealing and useful strategy for the synthesis of strained molecular belts but also a new paradigm for the fabrication of belt-derived chiroptical materials with high CPL activities.

Enhanced emission intensity in (Li+/Ca2+/Bi3+) ions co-doped NaLa(MoO4)2: Dy3+phosphors and their Judd-Ofelt analysis for WLEDs applications

In the present study, we have synthesized a series of Dy3+ ion doped NaLa(MoO4)2phosphors by the conventional solid-state method at 750 °C for 4h. All the compounds were crystallized in the tetragonal scheelite type structure with space group (I41/a, No.88). The morphology and functional group were confirmed by the field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared(FTIR)spectroscopy. Upon near-Ultraviolet (n-UV) excitation, the PL spectra exhibit the two characteristic emissions of Dy3+ ions, blue (4F9/2 → 6H15/2) at 487 nm and yellow (4F9/2 → 6H13/2) at 574nm respectively. The optimum concentration of Dy3+ionis 3 mol% and then quenching occurred due to multipolar interaction. Further, enhanced the emission intensity by co-doping with monovalent (Li+), divalent (Ca2+) and trivalent (Bi3+) ions. Among them, Li+ ion co-doped samples are shown maximum intensity (50 times) more than Dy3+ doped phosphors as relaxation of parity restriction of electric dipole transition because of local distortion of crystal field around the Dy3+ ions. In addition, by incorporation of Eu3+ ions into NaLa(MoO4)2:Dy3+system, tuned the emission color from white to red, owing to energy transfer from Dy3+ to Eu3+ ions. The intensity parameters (Ω2, Ω4) and radiative properties such as transition probabilities (A T), radiative lifetime (τ rad), and branching ratio were calculated using the Judd-Ofelt theory. CIE color coordinates, CCT values indicates that these phosphors exhibit an excellent white emission. The determined radiative properties, CIE and CCT results revealed that the Dy3+-activated NaLa(MoO4)2phosphors are potential materials for developing white LEDs, and optoelectronic device fabrications.

Extended MCDHF Calculations of Energy Levels and Transition Data for N i

Accurate and extensive atomic data are essential for spectroscopic analyses of stellar atmospheres and other astronomical objects. We present energy levels, lifetimes, and transition probabilities for neutral nitrogen, the sixth most abundant element in the cosmos. The calculations employ the fully relativistic multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods, and span the 103 lowest states up to and including 2s22p25s. Our theoretical energies are in excellent agreement with the experimental data, with an average relative difference of 0.07%. In addition, our transition probabilities are in good agreement with available experimental and theoretical data. We further verify the agreement of our data with experimental results via a reanalysis of the solar nitrogen abundance, with the results from the Babushkin and Coulomb gauges consistent to 2% or 0.01 dex. We estimated the uncertainties of the computed transition data based on a statistical analysis of the differences between the transition rates in the Babushkin and Coulomb gauges. Out of the 1701 computed electric dipole transitions in this work, 83 (536) are associated with uncertainties smaller than 5% (10%).

Stepwise Amplification of Circularly Polarized Luminescence in Chiral Metal Cluster Ensembles.

Chiral metal-organic frameworks(MOFs)are usually endowed by chiral linkers and/or guests. The strategy using chiral secondary building units in MOFsfor solving the trade-off of circularly polarized luminescence (CPL)-active materials, high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (|glum |) has not been demonstrated. This work directionally assembles predesigned chiral silver clusters with ACQ linkers through reticular chemistry. The nanoscale chirality of the cluster transmits through MOF's framework, where the linkers are arranged in a quasi-parallel manner and are efficiently isolated and rigidified. Consequently, this backbone of chiral cluster-based MOFs demonstrates superb CPL, high PLQYs of 50.3%, and |glum | of 1.2 × 10-2 . Crystallographic analyses and DFT calculations show the quasi-parallel arrangement manners of emitting linkers leading to a large angle between the electric and magnetic transition dipole moments, boosting CPL response. As compared, an ion-pair-direct assembly without interactions between linkers induces one-ninth |glum | and one-sixth PLQY values, further highlighting the merits of directional arrangement in reticular nets. In addition, a prototype CPL switching fabricated by a chiral framework is controlled through alternating ultraviolet and visible light. This work is expected to inspire the development of reticular chemistry for high-performance chiroptical materials.

QED radiative corrections to electric dipole amplitudes in heavy atoms

We use the radiative potential method to perform a detailed study of quantum electrodynamics (QED) radiative corrections to electric dipole (E1) transition amplitudes in heavy alkali-metal atoms Rb, Cs, Fr, and alkali-metal-like ions Sr+, Ba+, and Ra+. The validity of the method is checked by comparing with the results of rigorous QED in simple atomic potentials. We study the effects of core relaxation, polarization of the core by the E1 field, and valence-core correlations on QED, which are shown to be important in some cases. We identify several transitions for which the QED contribution exceeds the deviation between atomic theory and experiment.

A Comparative Study of Eu3+-Doped Sillenites: Bi12SiO20 (BSO) and Bi12GeO20 (BGO)

The spectroscopic properties of Eu3+-doped Bi12SiO20 (BSO) were investigated and compared with that of Eu3+-doped Bi12GeO20 (BGO). The emission properties and the absorption spectra have been measured at 10 K as well as at 300 K (room temperature). Luminescence was detected due to the direct excitation of the 5D0 level of Eu3+, as well as through the excitation of the 5D1 level. The Judd-Ofelt theoretical framework was used to compute the radiative lifetimes (τ) and the omega parameters (Ωλ). The electric dipole transition probabilities, asymmetry ratios (R), along with the branching ratios (β) were also determined based on the obtained experimental data. The strongest detected luminescence belongs to the 5D0 → 7F0 transition observed at 578 nm, similar to the BGO sillenite. Reasons for the major presence of the 5D0 → 7F0 emission, theoretically forbidden by the Judd-Ofelt Theory, were investigated and compared with that of the BGO sillenite. Obtained results showed that the strong 5D0 → 7F0 line is also present in Eu:BSO, indicating that this is a feature of the entire sillenite family and not just Eu:BGO.

Abnormal Eu3+ → Eu2+ Reduction in Ca9−xMnxEu(PO4)7 Phosphors: Structure and Luminescent Properties

β-Ca3(PO4)2-type phosphors Ca9-xMnxEu(PO4)7 have been synthesized by high-temperature solid-phase reactions. The crystal structure of Ca8MnEu(PO4)7 was characterized by synchrotron X-ray diffraction. The phase transitions, magnetic and photoluminescence (PL) properties were studied. The abnormal reduction Eu3+ → Eu2+ in air was observed in Ca9-xMnxEu(PO4)7 according to PL spectra study and confirmed by X-ray photoelectron spectroscopy (XPS). Eu3+ shows partial reduction and coexistence of Eu2+/3+ states. It reflects in combination of a broad band from the Eu2+ 4f65d1 → 4f7 transition and a series of sharp lines attributed to 5D0 → 7FJ transitions of Eu3+. Eu2+/Eu3+ ions are redistributed among two crystal sites, M1 and M3, while Mn2+ fully occupies octahedral site M5 in Ca8MnEu(PO4)7. The main emission band was attributed to the 5D0 → 7F2 electric dipole transition of Eu3+ at 395 nm excitation. The abnormal quenching of Eu3+ emission was observed in Ca9-xMnxEu(PO4)7 phosphors with doping of the host by Mn2+ ions. The phenomena of abnormal reduction and quenching were discussed in detail.

Isolated-core quadrupole excitation of highly excited autoionizing Rydberg states

The structure and photoexcitation dynamics of high lying doubly excited states of the strontium atom with high angular momenta are studied in the vicinity of the Sr$^+(N=5)$ threshold. The spectra recorded using resonant multiphoton isolated core excitation are analyzed with calculations based on configuration interaction with exterior complex scaling, which treats the correlated motion of the two valence electrons of Sr from first principles. The results are rationalized with a model based on multichannel quantum-defect theory and transition dipole moments calculated with a perturbative treatment of electron correlations. Together, both approaches reveal that most of the lines observed in the spectra arise from the interaction of a single optically active state, coupled to the initial state by an electric-dipole transition, with entire doubly-excited Rydberg series. The long-range electron correlations responsible for this interaction unexpectedly vanish for identical values of the initial and final principal quantum numbers, a fact related to the quasi hydrogenic nature of the high-$l$ Rydberg electron. This special situation, and in particular the vanishing interaction, leads to the surprising observation of an electric \emph{quadrupole} isolated-core excitation with a similar intensity as the neighboring electric dipole transitions.