Relative Oscillator Strengths Research Articles

On the effective vibrational temperature of the source using (2)3∏ - X3∏ system of GeC molecule

In this work, the experimental potential energy curves for (2)3Π and X3Π electronic states of GeC molecule have been constructed by using Rydberg-Klein-Rees (RKR) method. The radiative transition parameters viz., Franck-Condon (FC) factor, r-centroid, electronic transition moment, band strength, relative band strength, Einstein coefficients, radiative lifetime and oscillator strength for the (2)3Π−X3Π system of GeC molecule have been estimated for the experimentally observed vibrational levels from Rydberg-Klein-Rees (RKR) potential and the estimated values are tabulated. The estimated effective vibrational temperature found as 5628 K for the (2)3Π−X3Π system of GeC molecule. The radiative transition parameters and effective vibrational temperature are evident that the possible presence of GeC molecule in solar and sunspots atmosphere. Further, these parameters are employed in rationalizations of astrochemical and astrophysical observations.

Instigating the Asymmetry of Dy3+ Ions Doped in Borate Glasses for Photonic Device w-LED Applications

For usage in solid state white light emitting device applications, dysprosium-activated calcium aluminum barium sodium borate glass was synthesized. The detailed understanding of physical, optical, structural, and photo-luminescence characteristics was examined and compared. To comprehend the oscillator strength of the ligands in the prepared glasses, the Judd-Ofelt intensity characteristics were assessed. The Ω2 greater relative oscillator strength value shows highest for the prepared glasses suggesting their cause due to hypersensitive transitions. In comparison to other glasses in the research, the potential radiative transition probabilities, branching ratios, and stimulated emission cross-section for 575 nm emission all exhibited higher values. The stimulated emission cross-section shows highest for 0.3 mol% Dy2O3 content in the present glasses. The asymmetry of synthesizedglass sample ratio has been evaluated and compared using Yellow to Blue (Y/B) emission ratio. Study of the emission spectra and assessment of CCT and DUV values for the glasses reveal emission in the CIE diagram's white light zone.

Measurement of relative transition oscillator strength via Rydberg six-wave mixing spectrum

Atomic-based field measurements have made significant progress in reproducibility, accuracy, and resolution enhancement. In this paper, the relative transition oscillator strength of excited 6P[Formula: see text] to nD[Formula: see text]/nD[Formula: see text] can be measured more accurately by spectral results of Rydberg six-wave mixing, meanwhile accompanying measured efficiency of Rydberg electromagnetically induced transparent and fluorescence is compared. Relative transition oscillator strength is obtained and demonstrated, it is observed that relative transition oscillator strengths are independent of primary quantum n in thermal vapor. The measured results are approached with theoretical calculation which can not only extend relative transition oscillator strength of the measurement way in an atomic system, but can also demonstrate six-wave mixing as nonlinear process read information of laser excite atoms more accurately.

Isomerization-induced fluorescence enhancement of two new viologen derivatives: mechanism insight and DFT calculations.

The dark-colored viologen radical cations are unstable in air and easily fade, thus greatly limiting their applications. If a suitable substituent is introduced into the structure, it will have the dual function of chromism and luminescence, which will broaden its application field. Here, Vio1·2Cl and Vio2·2Br were synthesized by introducing aromatic acetophenone and naphthophenone substituents into the viologen structure. The keto group (-CH2CO-) on the substituents is prone to isomerize into the enol structure (-CH[double bond, length as m-dash]COH-) in organic solvents, especially in DMSO, resulting in a larger conjugated system to stabilize the molecular structure and enhance fluorescence. The time-dependent fluorescence spectrum shows obvious keto-to-enol isomerization-induced fluorescence enhancement. The quantum yield also increased significantly (T = 1 day, ΦVio1 = 25.81%, ΦVio2 = 41.44%; T = 7 days, ΦVio1 = 31.48%, and ΦVio2 = 54.40%) in DMSO. The NMR and ESI-MS data at different times further confirmed that the fluorescence enhancement was caused by isomerization, and no other fluorescent impurities were produced in solution. DFT calculations show that the enol form is almost coplanar throughout the molecular structure, which is conducive to stabilizing the structure and enhancing fluorescence. The fluorescence emission peaks of the keto and enol structures of Vio12+ and Vio22+ were at 416-417 nm and 563-582 nm, respectively. The fluorescence relative oscillator strength of Vio12+ and Vio22+ enol structures is significantly higher than that of keto structures (f value changes from 1.53 to 2.63 for Vio12+ and from 1.62 to 2.81 for Vio22+), indicating stronger fluorescence emission of the enol structure. The calculated results are in good agreement with the experimental results. Vio1·2Cl and Vio2·2Br are the first examples of isomerization-induced fluorescence enhancement of viologen derivatives, which shows strong solvatofluorochromism under UV light, making up for the disadvantage that it is easy for a viologen radical to fade in air, and providing a new strategy for designing and synthesizing viologen materials with strong fluorescence.

Photoluminescence properties of Dy3+ doped Sb2O3-Na2O-B2O3 glasses for laser applications

In present study Dy3+ doped 10Sb2O3–20Na2O–70B2O3 glasses of different concentration were synthesised by melt quenching protocol. The prepared glasses were subjected to the absorption and photoluminescence characterization. The absorption transitions related oscillator strengths have been utilized in the formulation of JO parameters. The bonding parameters along with lasing potential of the glasses were tabulated using JO parameters. Further, excitation and emission spectra of the glass exhibited the characteristic lines of the Dy3+ ion and its intensity varied with the doping concentration. The Y/B ratio of the glass was determined using emission spectra of the glass. The results suggest 1 mol% of Dy3+ doped glasses are useful for continuous yellow laser applications.

Resonant boron acceptor states in semiconducting diamond

High-excited discrete states of boron hydrogenlike acceptors in crystalline diamond have been measured by temperature-dependent infrared absorption spectroscopy. We distinguish the boron resonant states in diamond crystals from the localized boron states in the band gap by differentiating the impurity transitions within state continua of the valence light- and heavy-hole subbands on the basis of their relative oscillator strengths, specific selection rules, and temperature dependences. Constraints on the boron binding energy and spin-orbit splitting of the valence band have been derived by analysis of the structure of the infrared absorption spectra of boron-doped diamond, in particular by a comparison with boron spectra in other semiconductors with a diamond lattice.

Unconventional valley-dependent optical selection rules and landau level mixing in bilayer graphene

Selection rules are of vital importance in determining the basic optical properties of atoms, molecules and semiconductors. They provide general insights into the symmetry of the system and the nature of relevant electronic states. A two-dimensional electron gas in a magnetic field is a model system where optical transitions between Landau levels (LLs) are described by simple selection rules associated with the LL index N. Here we examine the inter-LL optical transitions of high-quality bilayer graphene by photocurrent spectroscopy measurement. We observed valley-dependent optical transitions that violate the conventional selection rules Δ|N| = ± 1. Moreover, we can tune the relative oscillator strength by tuning the bilayer graphene bandgap. Our findings provide insights into the interplay between magnetic field, band structure and many-body interactions in tunable semiconductor systems, and the experimental technique can be generalized to study symmetry-broken states and low energy magneto-optical properties of other nano and quantum materials.

First-Principles Study on Self-Activated Luminescence and 4f → 5d Transitions of Ce3+ in M5(PO4)3X (M = Sr, Ba; X = Cl, Br).

The origin of the self-activated luminescence in the apatite-type M5(PO4)3X (MPOX; M = Sr or Ba; X = Cl or Br) samples and the spectral assignment for cerium-doped Sr5(PO4)3Cl (SPOC) phosphors are determined from first-principles methods combined with hybrid density functional theory (DFT) calculations, using the standard PBE0 hybrid functional, with wave function-based embedded-cluster ab initio calculations (at the CASSCF/CASPT2/RASSI-SO level). Electronic structure calculations are performed in order to accurately derive the band gaps of the hosts, the locations of impurity states in the energy bands that are caused by native defects and doped Ce3+ ions, and the charge-compensation mechanisms of aliovalent doping. The calculations of defect formation energies under O-poor conditions demonstrate that the native defects are easily generated in the undoped MPOX samples prepared under reducing atmospheres, from which thermodynamic and optical transition energy levels, as well as the corresponding energies, are derived in order to interpret the luminescence mechanisms of the undoped MPOX as previously reported. Our calculations reveal that the self-activated luminescence is mainly attributed to the optical transitions of the excitons bound to the oxygen vacancies (VO), along with their transformation of the charge states 0 ↔ 1+. Furthermore, the eight excitation bands observed in the synchrotron radiation excitation spectra of SPOC: Ce3+, Na+ phosphors are successfully assigned according to the ab initio calculated energies and relative oscillator strengths of the 4f1 → 5d1-5 transitions for the Ce3+ ions at both the Sr(1) and Sr(2) sites in the host. It is hoped that the feasible first-principles approaches in this work are applied in order to explore the origins of the luminescence in undoped and lanthanide-doped phosphors, complementing the experiments from the perspective of chemical compositions and the microstructures of materials.

Rydberg excitons in electric and magnetic fields obtained with the complex-coordinate-rotation method

The complete theoretical description of experimentally observed magnetoexcitons in cuprous oxide has been achieved by Schweiner et al (2017 Phys. Rev. B 95 035202), using a complete basis set and taking into account the valence band structure and the cubic symmetry of the solid. Here, we extend these calculations by investigating numerically the autoionising resonances of cuprous oxide in electric fields and in parallel electric and magnetic fields oriented in [001] direction. To this aim we apply the complex-coordinate-rotation method. Complex resonance energies are computed by solving a non-Hermitian generalised eigenvalue problem, and absorption spectra are simulated by using relative oscillator strengths. The method allows us to investigate the influence of different electric and magnetic field strengths on the position, the lifetime, and the shape of resonances.

Ultrabroadband infrared near-field spectroscopy and imaging of local resonators in percolative gold films

Percolation processes are ubiquitous in nature and are responsible for many critical phenomena such as first-order phase transitions and infectious epidemic networks. The optical properties of a percolative medium can generally be captured by the effective medium approximation (EMA) when the degree of percolation and the properties of the constituent materials are properly addressed. However, the important local collective responses of nanoclusters in the deep subwavelength regime are often only phenomenologically addressed in the standard EMA formalism. A comprehensive method that measures local light–matter interactions and registers how the local responses influence global optical properties has yet to be established on a firm basis. In this paper, we use infrared nano-imaging/spectroscopy to investigate percolative gold films in the vicinity of the critical percolation threshold. We demonstrate experimentally and theoretically that the near-field spectra yield quantitative information of the characteristic length scale of the local gold clusters and their relative oscillator strengths. As a result, EMA analysis can be augmented with near-field nano-spectroscopy to yield better predictability of the far-field reflection spectrum at the corresponding spectral range.

Evaluation of molecular orbital symmetry via oxygen-induced charge transfer quenching at a metal-organic interface

Thin molecular films under model conditions are often exploited as benchmarks and case studies to investigate the electronic and structural changes occurring on the surface of metallic electrodes. Here we show that the modification of a metallic surface induced by oxygen adsorption allows the preservation of the geometry of a molecular adlayer, giving access to the determination of molecular orbital symmetries by means of near-edge X-ray absorption fine structure spectroscopy, NEXAFS. As a prototypical example, we exploited nickel tetraphenylporphyrin molecules deposited on a bare and on an oxygen pre-covered Cu(1 0 0) surface. We find that adsorbed atomic oxygen quenches the charge transfer at the metal-organic interface but, in contrast to a thin film sample, maintains the ordered adsorption geometry of the organic molecules. In this way, it is possible to disentangle π* and σ* symmetry orbitals, hence estimate the relative oscillator strength of core level transitions directly from the experimental data, as well as to evaluate and localize the degree of charge transfer in a coupled system. In particular, we neatly single out the σ* contribution associated with the N 1s transition to the mixed N 2px,y-Ni 3dx2-y2 orbital, which falls close to the leading π*-symmetry LUMO resonance.

Variation of the transition energies and oscillator strengths for the 3C and 3D lines of the Ne-like ions under plasma environment

We present the results of a detailed theoretical study which meets the spatial and temporal criteria of the Debye–Hückel approximation on the variation of the transition energies as well as the oscillator strengths for the (3C line) and the (3D line) transitions of the Ne-like ions subject to external plasma. Our study shows that the redshifts of the transition energy follow the general scaling behaviors similar to the ones for the simple H-like and He-like ions. Whereas the oscillator strength for the 3C line decreases, the oscillator strength for the spin-flipped 3D line increases as the strength of the outside plasma increases. As a result, their ratio is amplified subject to outside plasma environment. We further demonstrate that the plasma-induced variation between the relative strength of the 3C and 3D transitions is mainly due to the spin-dependent interactions which dictate the mixing of the 1P1 component in the 3D1 upper state of the 3D transition. In addition, we are able to find that the ratio between the relative oscillator strengths of the 3C and 3D lines in the presence of the plasma to their respective plasma-free values varies as a nearly universal function of , with Z the nuclear charge and D the Debye length. The results of this study should be of great help in the modelling and diagnostic of astrophysical plasmas as well as laboratory plasmas.

Site occupation and 4f → 5d transitions of Ce3+ ions at mixed Ca2+/Y3+ sites in CaYAlO4: Insights from first-principles calculations

The first-principles calculations in the combination of hybrid density functional theory (DFT) and multiconfigurational quantum-chemical methods are carried out to investigate geometric structures, electronic structures and 4f → 5d transitions of Ce3+ ions at mixed Ca2+/Y3+ sites in the CaYAlO4 (CYAO). The most energetically stable unit cell among three nonequivalent configurations is firstly determined according to the total energies from DFT calculations. The calculated defect formation energies of lanthanide dopants and complexes in the host (with relatively stable configurations) then reveal the preferred substitution of Ce3+ ions in the host. Moreover, the energies and relative oscillator strengths of the 4f → 5d transitions of Ce3+ at both Ca2+ and Y3+ sites are derived from the embedded-cluster quantum-chemical calculations at the CASSCF/CASPT2/RASSI−SO level. By comparison, the excitation bands in the experimental spectra of Ce3+-doped CYAO phosphors are mainly attributed to 4f → 5d transitions of Ce3+ ions at Ca2+ sites, which is well consistent with the conclusions attained from the calculations on defect formation energies. The computational framework presented in this study is beneficial to identify the occupation sites of lanthanide ions and assign the excitation bands of the experimental spectra for the phosphors with mixed sites or solid-solution structures.

Encapsulation of anticancer drug doxorubicin inside dendritic macromolecular cavities: First-principles benchmarks.

By using first-principles approaches based on Density Functional Theory, we explore the possibility of using dendritic macromolecular structures as carriers of the doxorubicin anticancer drug. In particular, we consider macromolecular cavities of different sizes composed of phenylene-, thiophene-, phenyl-cored thiophen- and thioazole-based dendrimers. The comparison between the optimized molecular geometries of the monomers and of the host-guest complexes reveals that only slight structural changes are observed in doxorubicin upon complexation. Also, the encapsulation energies for the host-guest complexes suggest that these systems are of potential use for pharmacology applications in vivo. The interaction of the guest doxorubicin with the macromolecular cavities exploits different types of weak intermolecular forces including σ, π and hydrogen bond interactions. The electronic structure of these complexes is discussed, with particular emphasis placed on the role of the charge distribution and the nature of the frontier molecular orbitals in the encapsulation process. Spectroscopic properties of these complexes are derived to facilitate their detection in laboratory and in vivo. These include IR vibrational frequencies, absorption wavelengths and relative oscillator strengths for the main transitions in the UV-Vis spectrum.

Excitons without effective mass: Biased bilayer graphene

Understanding the dynamics of excitons in two dimensional semiconductors requires a theory that incorporates the essential physics distinct from their three-dimensional counterparts. In addition to the modified dielectric environment, single-particle states with strongly non-parabolic dispersion appear in many two-dimensional band structures, so that "effective mass" is ill-defined. Focusing on electrostatically-biased bilayer graphene as an example where quartic (and higher) dispersion terms are necessary, we present a semi-analytic theory used to investigate the properties of ground and excited excitonic states. This includes determination of relative oscillator strengths and magnetic moments (g-factors) which can be directly compared to recent experimental measurements.

Selective Protonation of Unbounded Sodium Cholates for Reversible Blue-Shift Absorption Spectra of Single-Chirality Single-Walled Carbon Nanotube in Solution

In contradiction to the long-standing optical depletion of single-walled carbon nanotubes (SWCNT) by acid doping, this work reports the blue-shifted and optical density-increased S11 (the first Van Hove singularity transition) peak absorption spectra of single-chirality (6,5) SWCNT dispersed in specific surfactant compositions such as 1% SDS (sodium dodecyl sulfate) /1% SC (sodium cholate) and 2% SDS/0.5% SC, which were caused by addition of acid. These anomalous optical changes can be reversed by adding base, and they are discussed on the basis of surfactant arrangements on SWCNT sidewalls, which arose from the selective protonation of unbounded SC to shift the thermodynamic equilibrium of SC adsorbed SWCNT to the desorption of SC from SWCNT surface. The spectroscopic interpretation obeys the dipole moment transition related energy level variation and oscillator strength change.

Mixed Upper Exciton State of the Special Pair in Bacterial Reaction Centers.

Excitonic interactions between two closely separated bacteriochlorophyll a molecules (BChls) in the special pair of the reaction center (RC) of purple bacteria determine the positions and relative oscillator strengths of its two excitonic components. While the absorption of the lower excitonic band is well-defined, the position and the intensity of the upper excitonic band ( PY+) are still under debate. Recent 77 K two-dimensional electronic spectroscopy data on Rba. capsulatus suggested that the PY+ component absorbs at ∼840 nm, i.e., at a significantly lower energy than previously suggested. In the present work, we argue that the PY+ state is mixed with the excited states of the accessory BChls ( B*/ P Y+) leading to excitons contributing to the 785-825 nm spectral region which is consistent with previously published data. This conclusion is based on hole-burning/linear dichroism data and modeling studies of the excitonic structure of the RC using a non-Markovian reduced density matrix approach.

Внутридопплеровские резонансы, обусловленные осцилляциями Раби на атомных переходах в тонких газовых ячейках

Theoretical research is carried out of excitation of atoms from the ground quantum level to a metastable state by the running monochromatic radiation in thin gas cell, whose inner thickness is much less than its radius. As a result, sub-Doppler resonances has been discovered and analyzed, which appear in the population of the metastable atomic level at scan of the radiation frequency because of light induced Rabi oscillation on the given optical transition and also transit relaxation of atoms in the considered cell with the rarefied gas. Such nontrivial resonances may be detected in atomic fluorescence by additional probe light beam. The method for direct measurement of the Rabi frequency on spectral intervals between established sub-Doppler resonances is proposed. Obtained results may be applied in atomic spectroscopy for precise determination of components of matrix elements of dipole moments and related Einstein coefficients and oscillator strengths of quantum transitions between ground and metastable atomic levels.

Linear response time-dependent density functional theory of the Hubbard dimer

The asymmetric Hubbard dimer is used to study the density-dependence of the exact frequency-dependent kernel of linear-response time-dependent density functional theory. The exact form of the kernel is given, and the limitations of the adiabatic approximation utilizing the exact ground-state functional are shown. The oscillator strength sum rule is proven for lattice Hamiltonians, and relative oscillator strengths are defined appropriately. The method of Casida for extracting oscillator strengths from a frequency-dependent kernel is demonstrated to yield the exact result with this kernel. An unambiguous way of labelling the nature of excitations is given. The fluctuation-dissipation theorem is proven for the ground-state exchange-correlation energy. The distinction between weak and strong correlation is shown to depend on the ratio of interaction to asymmetry. A simple interpolation between carefully defined weak-correlation and strong-correlation regimes yields a density-functional approximation for the kernel that gives accurate transition frequencies for both the single and double excitations, including charge-transfer excitations. Many exact results, limits, and expansions about those limits are given in the appendices.

Geometric, electronic and optical properties of undoped and cerium-doped La5(Si2+xB1−x)(O13−xNx) solid solutions: A theoretical investigation

The geometric properties and electronic structures of La5(Si2+xB1−x)(O13−xNx) solid solutions and 4f→5d transitions in Cerium-doped La5Si2BO13 phosphors are studied by combining the hybrid density functional theory (DFT) calculations (with the standard PBE0 functional) and the wave function-based embedded cluster ab-initio calculations (with the CASSCF/CASPT2/RASSI–SO methods). The hybrid PBE0 calculations exhibit the site preferences of different atomic pairs and Ce3+ ion in hosts, and predict the variation trend of the band gap for the La5(Si2+xB1−x)(O13−xNx) with x varying between 0 and 1.0. The energies and relative oscillator strengths for 4f→5d transitions of Ce3+ ions (without and with N3- ion in their local environments) in the La5Si2BO13 host are derived from the embedded cluster ab-initio calculations. The experimental spectra of La5Si2BO13:Ce3+ phosphors are successfully assigned, according to the calculated schematic diagrams of 4f→5d transitions for Ce3+ ions in the host. On the basis of the various empirical models of Dorenbos, the energy locations of 4f ground states and the lowest 5d states of all the Ln3+ and Ln2+ ions in the La5Si2BO13 host are further derived from the ab-initio calculated 5d barycenter of Ce3+ ions as well as the experimental spectra.