Transition Oscillator Strengths Research Articles

Combined Experimental and Ab Initio Methods for Rationalization of Magneto-Luminescent Properties of YbIII Nanomagnets Embedded in Cyanido/Thiocyanidometallate-Based Crystals.

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [YbIII(2,2′-bipyridine-1,1′-dioxide)4]3+ single-molecule magnets by cyanido/thiocyanidometallate counterions, [AgI(CN)2]− (1), [AuI(SCN)2]− (2), [CdII(CN)4]2–/[CdII2(CN)7]3– (3), and [MIII(CN)6]3– [MIII = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all YbIII centers. They differ in the magnetic axiality; however, transversal g-tensor components are always large enough to explain the lack of zero-dc-field relaxation. The excited doublets lie more than 120 cm–1 above the ground one for all YbIII centers. It was confirmed by high-resolution emission spectra reproduced from the ab initio calculations that give reliable insight into energies and oscillator strengths of optical transitions. These findings indicate the dominance of Raman relaxation with the power n varying from 2.93(4) to 6.9(2) in the 4–3–5–1–2 series. This trend partially follows the magnetic axiality, being deeper correlated with the phonon modes schemes of (thio)cyanido matrices.

Effect of Electron Correlation and Breit Interaction on Energies, Oscillator Strengths, and Transition Rates for Low-Lying States of HeliumSupported by the National Key Research and Development Program of China (Grant No. 2017YFA0402300), and the National Natural Science Foundation of China (Grant Nos. 11774344 and 11474033).

The transition energies, E1 transitional oscillator strengths of the spin-allowed as well as the spin-forbidden and the corresponding transition rates, and complete M1, E2, M2 forbidden transition rates for 1s 2, 1s2s, and 1s2p states of He I, are investigated using the multi-configuration Dirac–Hartree–Fock method. In the subsequent relativistic configuration interaction computations, the Breit interaction and the QED effect are considered as perturbation, separately. Our transition energies, oscillator strengths, and transition rates are in good agreement with the experimental and other theoretical results. As a result, the QED effect is not important for helium atoms, however, the effect of the Breit interaction plays a significant role in the transition energies, the oscillator strengths and transition rates.

Transition spectral parameters of In-like Ba, La, and Ce ions

The spectral parameters (energy levels, wavelengths, transition probabilities, line strengths, and oscillator strengths) of resonance lines for Ba VIII, La IX, and Ce X have been obtained using the multiconfiguration Dirac–Hartree–Fock method, with contributions of quantum electrodynamics and Breit interaction corrections taken into consideration. The calculated results of energy levels and wavelengths are in good agreement with experimental values and other calculations. The number of energy levels and wavelengths considered is larger than that of any other experiment or other calculations. The transition probabilities, line strengths, and oscillator strengths are also calculated where no other theoretical results and experimental values are available.

Intracenter dipole transitions of a hydrogen-like boron acceptor in diamond: Oscillator strengths and line broadening

Substitutional boron in diamond acts as an acceptor center with the ionization energy of about 372 meV. Unlike its analogues in elemental semiconductors (silicon, germanium), boron bound states are poorly described by the electronic mass approximation due to the large ionization energy and the small spin-orbit splitting of the valence band in diamond. Thereby experimental investigations appear to be a main way of study of discrete electronic states of boron in diamond.In this paper, we report infrared (IR) absorption spectroscopy results obtained for HPHT-grown single crystal diamonds doped with natural boron (80% 11B – 20% 10B), and with isotopically enriched boron (99% 11B – 1% 10B). A moderate dopant concentration (1016–1017 cm−3), low concentration of lattice defects and vanishing thermal impact at cryogenic temperatures provided significantly reduced line broadening so that more than 60 boron transitions could be spectrally resolved. Mathematical approximation of the spectral lines revealed the main empiric features of zero-phonon dipole intracenter transitions: their energy, linewidth and integrated absorption. This allowed us to calculate oscillator strength of the boron acceptor transitions in diamond. The Lorentzian shape of the spectral lines indicates dominating uniform broadening of the transitions. Together with the relatively broad linewidths (0.1–0.5 meV) it reveals strong electron-phonon interaction in boron-doped diamond.

Spectroscopic and quantum chemical study on a non-linear optical material 4-[(1E)-3-(5-chlorothiophen-2-yl)-3-oxoprop-1-en-1-yl] phenyl4-methylbenzene-1-sulfonate

Chalcone derivatives are known for their characteristic non-linear optical efficiency. In the present work, the relation between the molecular structure and non-linear optical properties of a synthesized chalcone derivative 4-[(1E)-3-(5-chlorothiophen-2-yl)-3-oxoprop-1-en-1-yl] phenyl4-methylbenzene-1-sulfonate (4TPMS) have been investigated by combined experimental and theoretical approaches. The title compound 4TPMS was characterized by spectroscopic techniques viz. Raman, FT-IR, UV-vis, and 1H NMR. Further, the experimental findings were validated by quantum chemical computations. The crystalline geometry of 4TPMS was optimized to energy minima by employing density functional theory (DFT) with B3LYP/6-311++G(d,p) approximation level. Harmonic vibrational frequencies were calculated and the spectral assignments have been done by potential energy distribution (PED) analysis. Significant non-linear optical (NLO) responses of chalcone are mainly caused by charge delocalization between lone pair and antibonding molecular orbitals within the molecule. Hence, natural bond orbital (NBO) was performed to analyze the charge delocalization along with the stability of the molecule. The population analysis based on Charges from Electrostatic Potentials using a Grid based method (CHELPG) was employed to understand the electrophilic/nucleophilic reaction sites.Moreover, the time-dependent density functional theory (TD-DFT) was employed to predict the energies, absorption wavelengths (λmax) and oscillator strengths (f) of the electronic transitions. The TD-DFT calculation successfully reproduces the experimental UV-Vis spectrum of 4TPMS. The chemical shifts observed in 1H-NMR and the calculated GIAO shielding tensors also showed good agreement. A vibrational contribution to the NLO activity and the effect of charge delocalization on the NLO response were illustrated by comparing the similar kind of chalcone derivatives.

Computing molecular excited states on a D-Wave quantum annealer

The possibility of using quantum computers for electronic structure calculations has opened up a promising avenue for computational chemistry. Towards this direction, numerous algorithmic advances have been made in the last five years. The potential of quantum annealers, which are the prototypes of adiabatic quantum computers, is yet to be fully explored. In this work, we demonstrate the use of a D-Wave quantum annealer for the calculation of excited electronic states of molecular systems. These simulations play an important role in a number of areas, such as photovoltaics, semiconductor technology and nanoscience. The excited states are treated using two methods, time-dependent Hartree–Fock (TDHF) and time-dependent density-functional theory (TDDFT), both within a commonly used Tamm–Dancoff approximation (TDA). The resulting TDA eigenvalue equations are solved on a D-Wave quantum annealer using the Quantum Annealer Eigensolver (QAE), developed previously. The method is shown to reproduce a typical basis set convergence on the example hbox {H}_2 molecule and is also applied to several other molecular species. Characteristic properties such as transition dipole moments and oscillator strengths are computed as well. Three potential energy profiles for excited states are computed for hbox {NH}_3 as a function of the molecular geometry. Similar to previous studies, the accuracy of the method is dependent on the accuracy of the intermediate meta-heuristic software called qbsolv.

Multi-step Synthesis, Characterization and Photophysical Investigation of Novel Biologically Active Heterocyclic Chalcone (AECO).

Novel alkylated heterocyclic chalcone (E)-1-(2-(allyloxy)phenyl)-3-(9-ethyl-9H-carbazol-3-yl)prop-2-en-1-one (AECO) with extended π-bond was prepared by the multi-steps synthesis. The structure of the AECO was established by the spectroscopic technics and purity of the compound was confirmed by the elemental analysis. Physicochemical parameters of the AECO such as molar absorption coefficient, transition dipole moments, stokes shift, oscillator strength and fluorescence quantum yield were calculated in ten various solvents on the basis of polarity of the solvents to see the effect of the solvent with AECO. Interaction of the AECO chromophore with cationic CTAB and anionic SDS surfactants were determined by using the fluorescence spectroscopy techniques. The intensity of the florescence spectrum increase with increasing the concentrations of surfactants. This suggests that strong interaction occurs between AECO with surfactants and this interaction arise from electrostatic forces. So, AECO chromophore could be used as analysis to define the Critical Micelle Concentration (CMC) of the surfactants. In addition the in-vitro antibacterial active of novel heterocyclic chalcone agents four bacteria's strain were evaluated and result showed AECO is beater antibacterial agent against Gram-Negative Bacteria (E. coli and S. flexneri) as compare to the Gram Negative Bacteria with respected to the standard drug Tetracycline.

Structure elucidation by Sparkle/RM1, and solution behavior of lanthanideIII complexes: NMR, 4f‒4f absorption spectra and Photoluminescent properties

This paper presents the paramagnetic NMR, 4f‒4f absorption and photoluminescence properties of the complexes of Sm, Eu, Ho and Er with hexafluoroacetylacetone (hfaa) and 1,10‒phenanthroline (phen) in various coordinating and non‒coordinating solvents. The ground state molecular structure of the ternary complexes, [Ln(hfaa)3(phen)](Ln = Ho and Er) and their hydrated parent molecules, [Ln(hfaa)3(H2O)2] were determined using semi‒empirical Sparkle/RM1 method. The optimized structures reflect the effect of lanthanide contraction as the average bond distances [Ln‒O and Ln‒N] decreases on going from Ho to Er. The shape analyses reveal that the geometry of these eight-coordinated complexes is very close to triangular dodecahedron with D2d symmetry. The NMR spectra of the complexes show that the complexes are stable in both coordinating and non‒coordinating solvents. In the 4f‒4f absorption spectra, the solvents’ effect is reflected on the band shape and oscillator strength of the hypersensitive transitions of ternary Ho (5G6 ← 5I8) and Er (2H11/2 ← 4I15/2 and 4G11/2 ← 4I15/2) complexes. These changes suggest solvents influence in changing the symmetry of the field around the Ho and Er ions. The photophysical properties of Sm and Eu complexes are superior in non‒coordinating solvents than those observed in the coordinating solvents .

X-ray transient absorption reveals the 1Au (n\u03c0*) state of pyrazine in electronic relaxation

Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computations. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated in 200 ± 50 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

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

Branching fractions of 67 Cr I spectral lines, which covered a wavelength ranging from 213-541 nm, were measured by a high-resolution grating spectrometer which recorded the intensity of chromium emission spectrum from a hollow cathode discharge lamp. The corresponding transition probabilities and oscillator strengths were derived by the branching fractions obtained in this work combined with the radiative lifetimes reported in the previous literature.

Core-polarization corrected Dirac-Fock computations of one-electron spectra in the rubidium isoelectronic sequence: Mo VI through Pb XLVI

Core-polarization corrected Dirac-Fock computations were performed, under assumption of so-called one-electron spectrum over-imposed on multi-electron spectrum, to predict levels and oscillator strengths for lowest transitions of so far mostly unknown highly ionized spectra of the rubidium isoelectronic series from Tc VII through Pb XLVI. To evaluate the accuracy of our predictions, calculations were also made for Mo VI spectrum, where experimental and other theoretical data are available. Behavior of oscillator strengths along the isoelectronic sequence was studied, exhibiting some relativistic features for highly ionized systems. The effect of collapse of the 4p64f5/2,7/2 levels along the sequence leads to change in the level ordering between Rh IX (Z = 45) and Sn XIV (Z = 50) spectra. We also carefully monitored the influence of core polarization (CP) on both energy levels and oscillator strengths. For energy levels, the CP contributions are small and quickly diminish along the isoelectronic sequence. For oscillator strengths the CP influence is much more profound not only near the neutral end of the sequence but also for highly ionized spectra. Moreover, the relative CP contribution to oscillator strengths of the 4f5/2,7/2−5d3/2,5/2 transitions reaches extreme values in the vicinity of the collapse region, where the 4f5/2,7/2 levels fall below the 5d3/2,5/2 ones. Finally, the assumption of the so-called one-electron spectrum, i.e., arising from excitation of a single valence electron outside of the closed-shell core seems to be justified for all states in the spectra under consideration with exception of the 4f5/2,7/2 levels, which are heavily mixed with other states along the sequence.

Multicomponent perovskite superlattices

Multicomponent perovskite superlattices

Spectral Behavior and Photophysical Parameters of Dihydrophenanthro[9,10-e][1,2,4]Triazine Derivative Dyes in Sol-Gel and Methyl Methacrylate Polymer Matrices.

This paper deals with the optical and photophysical properties of dihydrophenanthro[9,10-e][1,2,4]triazine fluorescent dyes doped in Silicate based sol-gel and homo-poly methyl methacrylate (PMMA). Solid hosts were found to effect on the optical and photophysical parameters such as molar absorptivity, cross sections of singlet-singlet electronic absorption and emission spectra, excited state lifetime, quantum yield of fluorescence. The dipole moment of electronic transition, the length of attenuation and oscillator strength of electronic transition from So → S1 have been calculated. The dyes were pumped with different powers using 3rd harmonic Nd:YAG laser of 355nm and pulse duration 8ns, with a repetition rate at (10Hz). Good photostability for compounds 1 and 2 were attained. It was decreased to 49% & 54% and 46% & 40% of the initial ASE of dyes in sol gel and PMMA, respectively, after 55,000 pumping pulses at (10mJ/pulse). The dyes in sol-gel showed improved photostability compared with those in organic polymeric matrices.

Time-resolved cathodoluminescence investigations of AlN:Ge/GaN nanowire structures

Light emitting diodes represent a key technology that can be found in many areas of everydays life. Therefore, the improvement of the efficiency of such structures offers a high economic and ecological potential. One approach is electrostatic screening of the quantum-confined Stark effect (QCSE) in polar III-V heterostructures by n-type doping in order to increase the oscillator strength of electronic transitions in quantum structures. In this study, we analyzed the cathodoluminescene (CL) spectra of different functional parts of individual AlN/GaN nanowire superlattices and studied their decay characteristics with sub-nanosecond time resolution. This allows us to extract information about strain and electric fields in such heterostructures with an overall spatial resolution <100 nm. The samples, which were investigated in a temperature range from 10 to 300 K by using time-integrated cathodoluminescence spectroscopy (TICL) and time-resolved cathodoluminescence spectroscopy (TRCL) consist of GaN bottom and top layer and a 40-fold stack of GaN nanodiscs, embedded in AlN barriers that were doped with Ge. We show, that the QCSE is reduced with increasing doping concentration due to a screening of the internal electric fields inside GaN nanodiscs, resulting in a reduction of the carrier lifetimes and a blue shift of the emitted light. Due to the small diameter of the electron excitation beam CL offers the possibility to individually analyze the different functional parts of the nanowires.

Optical properties and laser prediction of strontium bismuth borate glasses doped with neodymium Ions

Neodymium strontium bismuth borate glass samples were prepared using the traditional technique of high-temperature melting. The optical absorption spectra of the studied samples were recorded at room temperature. Analyzing the recorded spectra, important optical parameters were determined; for example, refractive index, optical dielectric constant, the indirect optical band gap and Urbach energy. The calculated Judd-Ofelt parameters exhibited trend which is Ω2 > Ω6 > Ω4. Moreover, the experimental and calculated oscillator strengths of the radiative 4f transitions, their lifetimes τ, refractive indices n, the emission, absorption cross sections and the branching ratio β were all determined and investigated. Calculations of the optical gain coefficient for all emission peaks revealed the possibility to use the present glass in laser emission materials and optical communication applications.

Intrawell and interwell phonon-excitons in a CdS/CdSe/CdS asymmetric quantum well

Binding energies of intrawell and interwell excitons are studied in the CdS/CdSe/CdS asymmetric quantum well by varying right well sizes under polaronic effect. The transition energy, transition life time, oscillator strength and absorption coefficients are measured. The above properties are obtained in the influence of image charge potential included in the Hamiltonian. The optical absorption coefficients with the function of incoming photon energy are obtained. The results bring out that the peak of absorption coefficient is larger for the direct exciton than for the indirect exciton and the radiative lifetime for the indirect exciton is found to be higher.

Localization-limited exciton oscillator strength in colloidal CdSe nanoplatelets revealed by the optically induced stark effect

2D materials are considered for applications that require strong light-matter interaction because of the apparently giant oscillator strength of the exciton transitions in the absorbance spectrum. Nevertheless, the effective oscillator strengths of these transitions have been scarcely reported, nor is there a consistent interpretation of the obtained values. Here, we analyse the transition dipole moment and the ensuing oscillator strength of the exciton transition in 2D CdSe nanoplatelets by means of the optically induced Stark effect (OSE). Intriguingly, we find that the exciton absorption line reacts to a high intensity optical field as a transition with an oscillator strength FStark that is 50 times smaller than expected based on the linear absorption coefficient. We propose that the pronounced exciton absorption line should be seen as the sum of multiple, low oscillator strength transitions, rather than a single high oscillator strength one, a feat we assign to strong exciton center-of-mass localization. Within the quantum mechanical description of excitons, this 50-fold difference between both oscillator strengths corresponds to the ratio between the coherence area of the exciton’s center of mass and the total area, which yields a coherence area of a mere 6.1 nm2. Since we find that the coherence area increases with reducing temperature, we conclude that thermal effects, related to lattice vibrations, contribute to exciton localization. In further support of this localization model, we show that FStark is independent of the nanoplatelet area, correctly predicts the radiative lifetime, and lines up for strongly confined quantum dot systems.

Experimental and theoretical studies of the electrochemical properties of mono azo dyes derived from 2-nitroso-1- naphthol, 1-nitroso-2-naphthol, and C.I disperse yellow 56 commercial dye in dye-sensitized solar cell

Quantum chemical computational tools were used to investigate the charge transfer electron excitation of two mono azo dyes derived from 2-nitroso-1- naphthol, 1-nitroso-2-naphthol, and C.I Disperse Yellow 56 commercial dye. The studied compounds were experimentally synthesized and characterized using UV-Vis and FT-IR spectrophotometry. Theoretical calculations were conducted with the synthesized dyes using density functional theory (DFT) and time-dependent DFT with 6-311+G(d,p) basis set in acetone, chloroform, DMSO, ethanol, gas, and water respectively. The solvent model (CPCM) is used in the calculations. The photovoltaic properties of the studied compounds were analyzed in terms of open-circuit voltage (Voc), electron injection, light-harvesting efficiency (LHE), HOMO-LUMO, and energy gap. The highest oscillator strength transition is observed at the HOMO–LUMO region of all the studied dyes molecules at 0.0534, 0.0012, 0.0048, 0.0543, 0.0542, 0.0024, 0.0074, 0.0534, 0.4903, 0.0531 for dye DA, DB, and DC in the various solvents respectively. Dye DC and DB gave the highest energy gap in acetone, DMSO, ethanol, gas, water, and chloroform media respectively. Interestingly, the LHE of the dyes was high in all the solvents used with the highest result obtained in acetone at 0.7308 for dye DC. The ∆Greg varies between -10.5 eV to11.8 eV in all the studied solvents which indicates a high electron injection capacity within the studied dyed molecules. The open-circuit voltage Voc, the ΔGinject and ΔGreg values for the selected molecule play a vital role in the comparison of both the selected dyes and thus they can be regarded as promising molecules for application in dye-sensitized solar cells.

Designing and theoretical characterization of benzodithiophene dione based donor molecules for small molecule organic solar cells

A series of novel A1-A2-D-A2-A1 type four small donor molecules named SM1-SM4 have been designed based on a common dual accepting benzodithiophene dione unit. These donor molecules were designed by replacing end-capped (rhodanine) acceptors of already synthesized SBDT-BDD (reference R) molecule with 2-methylenemalononitrile (A1a) forming SM1, methyl 2-cyanoacrylate (A1b) forming SM2, 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (A1c) forming SM3 and 1,4-dimethyl-5-methylene-2,6-dioxo-1,2,5,6-tetrahydropyridine-3-carbonitrile (A1d) forming SM4 molecule. The geometry optimization and theoretical characterization were carried out using reliable DFT at hybrid CAM-B3LYP/6–31G (d,p) level of theory. The photophysical, opto-electronic and wavelength dependent parameters of newly structured donors were computed and their resulting charge mobilities, maximum absorptions as well as exciton dynamics have been well addressed with respect to SBDT-BDD reference. Amongst all, SM3 exhibited maximum absorption at 484.2 nm due to its lowest energy bandgap (4.14 eV). It also exhibited lowest values of first singlet transition energy (2.56 eV), oscillator strength (1.01) and exciton binding energy (0.48 eV) because of its functionalization with strong electron withdrawing group (A1c). Moreover, the higher dipole moments, comparable hole and electron mobilities and higher values of Voc of SM1 and SM4 than R indicate the worth of these molecules being utilized as efficient donors in future OSC’s.

Experimental transition probabilities and oscillator strengths of doubly ionised krypton in the ultraviolet region

We report 62 new experimentally obtained transition probabilities (oscillator strengths) for doubly ionized krypton within the ultraviolet wavelength region (213 – 362) nm. The transition probabilities were obtained combining measured intensities of spectral lines emitted by a plasma generated in a low-pressure pulsed arc with theoretical oscillator strengths of 12 lines used as a reference. The plasma temperature ranged from 26,200 to 29,200 K and the electron density was in the range (1.7−3.2)×1022 m−3.