Transition Intensities Research Articles

Photon energy dependent appearance and disappearance of magnetic dipole transition in Gd2Hf2O7:Sm3+ nanophosphors

Tuning the light emission from rare earth ions in host materials can be controlled by relative intensity of electric and magnetic dipole transitions (EDT and MDT). This work reports an investigation on photon energy and dopant local site endowed appearance-disappearance of magnetic dipole transition in pyrochlore Gd2Hf2O7:Sm3+ (GHOS) nanophosphors. This is utilized in achieving color tunable luminescence in GHOS nanocrystals by photon energy manipulations and local site engineering. DFT calculated formation energy showed the distribution of Sm3+ at both Gd3+ and Hf4+ sites. Excitation with charge transfer band (CTB at ∼275 nm) leads to both EDT and MDT endowed by excitation of both Sm@Gd and Sm@Hf sites. On the other hand, excitation with f-f band (∼405 nm) selectively excites Sm@Hf site and completely quenches MDT leading to pure red emission. Luminescence lifetime population analysis shows that CTB excites Sm@Gd and Sm@Hf sites with equal probability leading to yellowish orange emission whereas f-f band excitation exclusively excites Sm@Hf site generating pure red light. This work represents a way forward in the areas of understanding structure-property correlation, local site/photon energy induced color tunability, and modulating local structure of lanthanide dopants of phosphors.

Thickness Dependence of Electronic Structure and Optical Properties of F8BT Thin Films.

Electronic devices based on polymer thin films have experienced a tremendous increase in their efficiency in the last two decades. One of the critical factors that affects the efficiency of polymer solar cells or light emitting devices is the presence of structural defects that controls non-radiative recombination. The purpose of this report is to demonstrate a non-trivial thickness dependence of optoelectronic properties and structure (dis)order in thin conductive poly(9,9-dioctyfluorene-alt-benzothiadiazole), F8BT, polymer films. The UV-Vis absorption spectra exhibited blue shift and peak broadening; significant changes in 0–0 and 0–1 radiative transition intensity was found in photoluminescence emission spectra. The density of state (DOS) was directly mapped by energy resolved-electrochemical impedance spectroscopy (ER-EIS). Satellite states 0.5 eV below the lowest unoccupied molecular orbital (LUMO) band were revealed for the thinner polymer films. Moreover, the decreasing of the deep states density in the band gap manifested an increment in the material structural ordering with increasing thickness. Changes in the ratio between crystalline phases with face-on and edge-on orientation of F8BT chains were identified in the films by grazing-incidence wide angle X-ray scattering technique. A thickness threshold in all investigated aspects of the films at a thickness of about 100 nm was observed that can be attributed to the development of J-H aggregation in the film structure and mutual interplay between these two modes. Although a specific structure–property relationship thickness threshold value may be expected for thin films prepared from various polymers, solvents and under different process conditions, the value of about 100 nm can be generally considered as the characteristic length scale of this phenomenon.

Photoexcitation of Ge76

The dipole strength of the nuclide $^{76}$Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.8 and 12.3 MeV at the $\gamma$ELBE facility. We identified 210 levels up to an excitation energy of 9.4 MeV and assigned spin $J$ = 1 to most of them. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\gamma$-ray cascades. The photoabsorption cross section up to the neutron-separation energy was determined and is compared with predictions of the statistical reaction model. The derived photon strength function is compared with results of experiments using other reactions.

Crystal growth and f – f transition intensities analysis of praseodymium ions in yttrium-aluminum orthoborates

A Pr3+ : YAl3(BO3)4 crystal with sizes of 20 × 10 × 10 mm was grown from high-temperature solution and its structural and spectroscopic properties were investigated. The distribution coefficient of praseodymium ranged from 0.6 to 0.8, that yield to the Pr3+ ion concentration of 1.1 ⋅1020 cm–3. Visible and infrared groundstate absorption (3H4) was measurement in dependence on the polarisation. The absorption spectra of the Pr3+ : YAl3(BO3)4 exhibit pronounced polarisation anisotropy. The modified Judd – Offelt theory was applied to evaluate the transitions intensities in absorption and emission, branching ratios and radiative lifetimes of the metastable levels 3P0 and 1D2.

Effect of aluminum substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics: A first-principles study

The paper sheds light on the effect of Al substitution on structural, electronic and dielectric properties of cubic CaCu3Ti4O12 ceramics based on first principles method. The CaCu3Ti4-xAlxO12 (x = 0, 0.5, 1, 1.5 and 2) ceramics still keeps a cubic lattice, and the lattice constant decreases with Al concentration enhanced. Phonon dispersion curves show that the structures of CaCu3Ti4-xAlxO12 ceramics are thermodynamically stable at x ≤ 1. The CaCu3Ti4-xAlxO12 ceramics have magnetic semiconductor properties and the band gaps corresponding to the high symmetry point G increases with increasing Al concentration. It can be concluded that doping Al can increase the dielectric constant and electronic transition intensity of cubic CaCu3Ti4O12 ceramics, and reduce its energy loss. In the low energy region, the dielectric constant of CaCu3Ti3.5Al0.5O12 ceramics is about ten times that of cubic CaCu3Ti4O12 ceramics. The ratio of aluminum atoms to titanium atoms of 1:7 May be the best ratio. It can also be concluded that when A13+ replaces Ti4+ ions, A1 also acts as an electron acceptor to reduce the electron concentration of Ti4+ ions, leading to the generation of oxygen vacancies. These results will provide a theoretical basis for the design of high dielectric constant materials.

A flexible approach to vibrational perturbation theory using sparse matrix methods.

A sparse linear algebra based implementation of Rayleigh-Schrödinger vibrational perturbation theory is presented. This implementation allows for flexibility in the coordinates used to expand the vibrational Hamiltonian as well as the order to which the perturbation theory is performed. It also provides a powerful tool for investigating the origin of spectral intensity and transition frequencies. Specifically, this flexibility allows for the analysis of which terms in the expansions of the Hamiltonian and dipole surface lead to the largest corrections to the energies and transition intensities, and how these conclusions depend on the coordinates used for these expansions. Comparisons of corrections to transition frequencies are reported for the Morse oscillator when the potential is expanded in Δr and Morse coordinates as well as for water, water dimer, and peroxynitrous acid when the molecular Hamiltonians and dipole surfaces are expanded in Cartesian displacement coordinates and in the displacements of the bond-angle-dihedral internal coordinates. Further comparisons of the corrections to the transitions moments are made for H2O and (H2O)2. It is found that while the transition frequencies and intensities are independent of coordinate choice, a good choice of coordinates leads to a cleaner interpretation of the origins of the anharmonicities in these systems.

Luminescence and optical thermometry based on silico-carnotite Ca3Y2Si3O12: Pr3+ phosphor

The photoluminescence and temperature sensitivities of Ca3Y2Si3O12:Pr3+ thermo-phosphors with silico-carnotite structure obtained by solid state reaction method were investigated. Pr3+ ions were accommodated in the A sites having coordination number of 9 in AB2C2(SiO4)3 to replace Y3+ ions. The typical sample consisted of microcrystals with an irregular structure and the surface of particles was smooth, which could enhance the luminescence due to reducing the scattering and non-radiation produced by rough surfaces. The band gap value of typical sample was about 4.01 eV. Dipole-dipole interaction could account for concentration quenching. The two thermometry strategies including normalized intensities from 3P0→3H4 transition and Fluorescence intensity ration (FIR) of 3P0→3H4/3P1→3H5 transitions were employed for temperature sensing in 298–573 K. The results revealed that Ca3Y2Si3O12:Pr3+ thermo-phosphors had good temperature sensitivity performance with maximum Sr of 0.59% K−1@573 K and 0.762% K−1@298 K in the above two methods, respectively. Hence, Ca3Y2Si3O12:Pr3+ would be a promising candidate in the field of optical thermometry.

Motif Transition Intensity: A Novel Network-Based Early Warning Indicator for Financial Crises

Financial crisis, rooted in a lack of system resilience and robustness, is a particular type of critical transition that may cause grievous economic and social losses and should be warned against as early as possible. Regarding the financial system as a time-varying network, researchers have identified early warning signals from the changing dynamics of network motifs. In addition, network motifs have many different morphologies that unveil high-order correlation patterns of a financial system, whose synchronous change represents the dramatic shift in the financial system’s functionality and may indicate a financial crisis; however, it is less studied. This paper proposes motif transition intensity as a novel method that quantifies the synchronous change of network motifs in detail. Applying this method to stock networks, we developed three early warning indicators. Empirically, we conducted a horse race to predict ten global crises during 1991–2020. The results show evidence that the proposed indicators are more efficient than the VIX and the other 39 network-based indicators. In a detailed analysis, the proposed indicators send sensitive and comprehensible warning signals, especially for the U.S. subprime mortgage crisis and the European sovereign debt crisis. Furthermore, the proposed method provides a new perspective to detect critical signals and may be extended to predict other crisis events in natural and social systems.

Site symmetry dependence on luminescence emission of Y2O3:Eu3+ dispersed in silica matrix

ABSTRACT Lanthanide ion (Ln3+) doped Y2O3 materials are used in making display devices. Ln3+ ions can occupy C2 and S6 sites in Y2O3. In many reported papers, Ln3+ ions occupy more C2 site leading to enhanced luminescence intensity of electric dipole transition as compared to that of magnetic dipole transition. In this study, we have prepared Eu3+ ion doped Y2O3 particles dispersed in silica (SiO2) using urea hydrolysis at 165°C. Among the prepared samples lower heated sample show cubic phase Y2O3 wherease 1400oC show α-Y2Si2O7 and all the samples show the luminescence characteristics of Eu3+. In Y2O3:Eu-SiO2, the as-prepared, 500 and 900°C heated samples show the higher luminescence intensity for the electric dipole transition than that of magnetic dipole transition and it is opposite upon annealed at 1400°C. It confirms that Eu3+ ions in as-prepared, 500 and 900°C heated samples occupy C2 site (asymmetric environment), whereas in 1400°C heated sample, they occupy the S6 site (symmetric environment). However, microparticles of the Y2O3:Eu sample annealed at 1400°C show that Eu3+ ions occupy more C2 site as compared to the S6 site. This study suggests that occupancy of C2 and S6 sites in Y2O3 by Eu3+ ions can be varied by surrounding medium as well as heat-treatment temperature.

Effective mass of cavity-vibration polaritons formed in etalons with liquid carbon tetrachloride.

Etalons are pairs of parallel plate mirrors with wavelength-scale spacing that exhibit cavity modes, giving transmission maxima (fringes) due to constructive interference. Infrared transmission measurements as a function of angle were used to determine the effective mass of etalon cavity modes using a gap filled with air and then liquid carbon tetrachloride. The air-filled etalon gives results in agreement with pure photon expectations established herein. Liquids with vibrations having strong infrared transition intensity (vibrational strong coupling mode) can strongly perturb the pattern of transmission resonances, creating mixed states of infrared cavity modes and molecular vibrations, i.e., cavity-vibration polaritons. The effective mass of one cavity-vibration polariton close to the strong vibration of carbon tetrachloride is 4.36 times heavier than the pure photon cavity mode expectation, i.e., the mass factor vs pure light. The mass factors are largest when closest to the strong vibrational frequency, and they converge to the one far away from the strong vibration. This work gives quantitative values of the effective mass of cavity-vibration polariton states and is a diagnostic for the mixing of vibrations with etalon transmission.

Stopping and restarting PrEP and loss to follow-up among PrEP-taking men who have sex with men and transgender women at risk of HIV-1 participating in a prospective cohort study in Kenya.

ObjectiveTo assess frequency and predictors of switching between being on and off PrEP and being lost to follow‐up (LTFU) among men who have sex with men (MSM) and transgender women (TGW) with access to PrEP services in Sub‐Saharan Africa.MethodsThis was a prospective cohort study of MSM and TGW from coastal Kenya who initiated daily oral PrEP from June 2017 to June 2019. Participants were followed monthly for HIV‐1 testing, PrEP refill, risk assessment and risk reduction counselling. Follow‐up was censored at the last visit before 30 June 2019, or the last HIV‐1‐negative visit (for those with HIV‐1 seroconversion), whichever occurred first. We estimated transition intensities (TI) and predictors of switching: (i) between being off and on PrEP; and (ii) from either PrEP state and being LTFU (i.e. not returning to the clinic for > 90 days) using a multi‐state Markov model.ResultsIn all, 134 participants starting PrEP were followed for a median of 20.3 months [interquartile range (IQR): 7.7–22.1]. A total of 49 (36.6%) people stopped PrEP 73 times [TI = 0.6/person‐year (PY), 95% confidence interval (CI): 0.5–0.7] and, of these, 25 (51.0%) restarted PrEP 38 times (TI = 1.2/PY, 95% CI: 0.9–1.7). In multivariable analysis, stopping PrEP was related to anal sex ≤ 3 months, substance‐use disorder and travelling. Restarting PrEP was related to non‐Christian or non‐Muslim religion and travelling. A total of 54 participants were LTFU: on PrEP (n = 47, TI = 0.3/PY, 95% CI: 0.3–0.5) and off PrEP (n = 7, TI = 0.2/PY, 95% CI: 0.1–0.4). In multivariable analysis, becoming LTFU while on PrEP was associated with secondary education or higher, living in the area for ≤ 1 year, residence outside the immediate clinic area and alcohol‐use disorder.ConclusionsSwitching between being on and off PrEP or becoming LTFU while on PrEP was frequent among individuals at risk of HIV‐1 acquisition. Alternative PrEP options (e.g. event‐driven PrEP) may need to be considered for MSM and TGW with PrEP‐taking challenges, while improved engagement with care is needed for all MSM and TGW regardless of PrEP regimen.

Clarifying the structure of low-lying states in Br72

The spins and parities of low-lying states in $^{72}\mathrm{Br}$ populated in the $\ensuremath{\beta}$ decay of $^{72}\mathrm{Kr}$ have been studied via conversion electron spectroscopy. The measurements were carried out at ISOLDE using a miniorange spectrometer with Si(Li) and HPGe detectors for electrons and $\ensuremath{\gamma}$ ray detection. Results of the conversion coefficients corresponding to transitions deexciting 12 levels in $^{72}\mathrm{Br}$ are reported. The multipolarities of the transitions are deduced and the spins and parities of the levels involved are discussed. From the multipolarities of the most intense transitions to the ground state, the spin and parity of the $^{72}\mathrm{Br}$ ground state have been definitely established as ${1}^{+}$. The spin of the 101.2-keV isomeric state is determined to be ${3}^{\ensuremath{-}}$. The level scheme is compared with mean-field and shell-model calculations and oblate deformation for the $^{72}\mathrm{Br}$ ground state is deduced. No $E0$ transitions have been found in $^{72}\mathrm{Br}$. $E0$ transitions in the neighboring isobaric nuclei, $^{72}\mathrm{Se}$ and $^{72}\mathrm{Ge}$, have also been studied.

Orbital localization and the role of the Fe and As 4p orbitals in BaFe2As2 probed by XANES

The polarization dependence of the near edge x-ray absorption spectroscopy (XANES) is an element specific probe to the real-space distribution of the density of unoccupied states in solid-state materials. In this paper, we present Fe and As $K$-edge experiments of Ba(Fe$_{1-x}$$M_{x}$)$_{2}$As$_{2}$ ($M=$ Mn, Co and $x=0.0$ and $0.08$). The experiments reveal a strong polarization dependence of the probed XANES spectra, which concerns mainly an increase of the intensity of electronic transitions when the beam polarization is set out of the sample's $ab$ crystallographic plane. The results show that states with $p_{z}$-orbital character dominate the density of unoccupied states close to the Fermi level. Partial substitution of Fe by Co is shown to decrease the intensity anisotropy, suggesting that Co promotes electronic transfer preferentially to states with $p_{z}$-orbital character. On the other hand, Mn substitution causes the increase of the spectra $p_{z}$-orbital anisotropy, which is proposed to take place by means of an enhanced local Fe $3d4p$ mixing, unveiling the role of Fe $4p$ states in the localization of the Fe $3d$ orbitals. Moreover, by comparing our results to previous experiments, we identify the relative mixing between Fe and the pnictide $4p_{x,y,z}$ orbitals as a clear divide between the electronic properties of iron arsenides and selenides. Our conclusions are supported by multiple-scattering theory calculations of the XANES spectra and by quantum chemistry calculations of Fe coordination electronic structure.

Role of interlayer coupling in second harmonic generation in bilayer transition metal dichalcogenides

Little is known about the role of weak interlayer coupling in the second harmonic generation (SHG) effects of two-dimensional van der Waals (vdW) systems. In this article, taking homo-bilayer $MoS_2/MoS_2$ and hetero-bilayer $MoS_2/MoSe_2$ as typical examples, we have systemically investigated their SHG susceptibilities as a function of interlayer hopping strength using first-principles calculations. For the SHG at zero frequency limit of both $MoS_2/MoS_2$ and $MoS_2/MoSe_2$, although the increase of tint can increase the intensities of interlayer optical transitions (IOT), the increased band repulsion around G point can eventually decrease their SHG values; the larger the tint, the smaller the SHG response. For the SHG spectra of $MoS_2/MoSe_2$ in the low photon-energy region, opposite to the $MoS_2/MoS_2$, their peak values are very sensitive to the variable tint, due to the strong $t_{int}$-dependent IOT dominating in the band edge; the larger the tint, the larger the SHG. For the SHG of $MoS_2/MoS_2$ in the high photon-energy region, comparing to the $MoS_2/MoSe_2$, their peak values will decrease in a much more noticeable way as the $t_{int}$ increases, due to the larger reduction of band nesting effect. Our study not only can successfully explain the puzzling experimental observations for the different SHG responses in different bilayer transition-metal dichalcogenides under variable tint, but also may provide a general understanding for designing controllable the SHG effects in the vdW systems.

Infrared Spectra of Hydrogen-Bonded Molecular Complexes Under Spatial Confinement.

Infrared (IR) spectroscopy is commonly used in chemical laboratories to study the geometrical structure of molecules and molecular complexes. The analysis of experimental IR spectra can nowadays be reliably supported by the results of quantum-chemical computations as vibrational frequencies and corresponding vibrational transition intensities are routinely calculated using harmonic approximation by virtually all quantum chemistry packages. In the present study we combine the methodology of computing vibrational spectra using high-level electron correlation treatments with an analytical potential-based approach to take into account spatial confinement effects. Using this approach, we perform a pioneering analysis of the impact of the spatial confinement caused by a cylindrical harmonic oscillator potential on the harmonic vibrational transition intensities and frequencies of two hydrogen-bonded complexes: HCN…HCN and HCN…HNC. The emphasis is put on the largest-intensity bands, which correspond to the stretching vibrations. The obtained results demonstrate that embedding the molecular complexes in an external confining potential causes significant changes of transition intensities and vibrational frequencies.

High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region.

First high-resolution spectra of cold (∼35K) singlet bromomethylene HCBr in the CH stretching (v1) region from 2770 to 2850cm-1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1-40:1) and rotationally assigned to (i) the CH stretch fundamental (v1) band X̃1,0,0←X̃0,0,0 and (ii) vibrational hot bands [X̃(1,1,0)←X̃(0,1,0) and X̃(1,0,1)←X̃(0,0,1)] arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H-C-Br bend (v2) or C-Br stretch (v3) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38cm-1) in good agreement with previous low-resolution fluorescence studies [M. Deselnicu et al., J. Chem. Phys. 124(13), 134302 (2006)]. Detailed analysis of the fundamental v1 band highlights the presence of perturbations in the X̃1,0,0 level, which we tentatively attribute to arise from the nearby triplet state ã(0,0,1) through spin-orbit interaction or the multiple quanta X̃0,2,1 singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60MHz) in the slit-jet IR spectrometer permits for clear observation of a nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies [C. Duan et al., J. Mol. Spectrosc. 220(1), 113-121 (2003)]. Finally, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than that predicted by using a bond-dipole model, which from high level ab initio quantum calculations [CCSD(T)/PVQZ] can be attributed to vibrationally induced "charge-sloshing" of electron density along the polar C-Br bond.

Стохастическое моделирование каскадных сценариев возникновения и развития чрезвычайных ситуаций

Introduction. The development of methods for modeling the flows of events in the occurrence and development of emergency and critical states, designed to solve the problems of supporting the management of rapid response to incidents in conditions of incomplete information, as well as the generation of preventive algorithms for rapid response in emergency situations, seems to be a promising direction for improving information and analytical support of management in security systems. The purpose of the research is to create mathematical tools for predicting emergency and critical conditions in local incidents based on discrete-event modeling of the dynamics of emergency situations. Methods of stochastic modeling are based on the representation of a cascade scenario of the dynamics of the development of accidents and catastrophes by a Markov process using a three-parameter Weibull distribution to set the intensities of transitions between emergency and critical states of adjacent levels. Results and discussion. A general stochastic model is constructed that describes the dynamics of the occurrence and development of accidents and catastrophes of technogenic and natural origin initiated by local incidents according to a cascade scenario with a branching structure with a set of possible elementary states represented in the form of a stratified graph. The main stages of the emergence and development of emergency situations are considered within the framework of the proposed representation of the cascade model by a Markov process with discrete states and continuous time. The expediency of local modeling of individual stages is substantiated based on the description of transitions between states of adjacent levels. Local systems of differential equations corresponding to some of the most probable scenarios for the development of events in the event of incidents are given. Non-stationary solutions of differential equations of Kolmogorov-Chapman are obtained, with assignment of intensities of transitions by three-parameter Weibull distributions. Conclusions. The proposed stochastic model makes it possible to predict the dynamics of the development of emergency and critical states according to a cascade scenario, and also reflects the probability characteristics of the timeliness and effectiveness of possible impacts in a prompt response to incidents. Keywords: stochastic modeling of technogenic accidents, cascade development of accidents and catastrophes, Weibull distribution.

Modulation of the magnetic and photophysical properties in 3d-4f and 4f-4f' heterobimetallic complexes involving a tetrathiafulvalene-based ligand.

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)3·2H2O/Dy(tta)3·2H2O (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetonate) and M(hfac)2·2H2O leads to the formation of heteroleptic 3d-4f dinuclear complexes of formula [MLn(hfac)5(L)]n (M(II) = Cd, Zn, Co, Mn, Ni and Ln(III) = Dy, Yb, Nd) and [ZnDy(tta)2(hfac)3(L)]·(CH2Cl2). Their X-ray structures reveal that the two coordination sites are occupied by one Ln(III) ion and one M(II) transition metal respectively. The M(II) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N2O4 coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N3O6 surrounding. When Dy(III) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb(III) is used, intense, moderated or quenched 2F5/2 → 2F7/2 NIR luminescence is observed when the Yb(III) ion is respectively associated with the Zn(II), Mn(II) and Ni(II)/Co(II) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d-d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f-4f' dinuclear complexes of formula [Ln2-xLn'x(hfac)6(L)]·a(CH2Cl2)·b(C6H14) and [Dy1.11Nd0.89(tta)3(hfac)3(L)]. The coordination selectivity is based on the radius. Among the 4f-4f' series, the Dy(III) derivatives displayed such ion in N2O6 eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy1.21Nd0.79(hfac)6(L)]·2(CH2Cl2)·(C6H14), [Yb1.04Nd0.96(hfac)6(L)] and [YbPr(hfac)6(L)] displayed respectively Nd(III), modarated Yb(III) and intense Yb(III) NIR emissions.

Computational analysis, Urbach energy and Judd-Ofelt parameter of warm Sm3+ complexes having applications in photovoltaic and display devices.

In this work, six reddish orange Sm3+ complexes were synthesized using organic ligand (L) and secondary ligands having hetero atoms by a one-step significant liquid-assisted grinding method and were characterized by spectroscopic techniques. The Urbach energy and band gap energy of the complexes were inspected by a linear fit. Using a least square fitting method, the Judd-Ofelt parameter and radiative properties were also determined. Thermal analysis, colorimetric analysis, luminescence decay time and anti-microbial properties of complexes were studied. The luminescence emission spectra of binary and ternary complexes displayed three characteristic peaks at 565, 603 and 650 nm in the powder form and four peaks at 563, 605, 646 and 703 nm in a solution phase due to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions respectively. The most intense transition in the solid phase (4G5/2 → 6H7/2) is accountable for orange color, and in the solution form, the highly luminescent peak (4G5/2 → 6H9/2) is responsible for reddish orange color of Sm3+ complexes. PXRD and SEM analyses suggested that the complexes possess a nanoparticle grain size with crystalline nature. The decent optoelectrical properties of title complexes in the orangish-red visible domain indicated possible applications in the manufacturing of display and optoelectronic devices.

Spectroscopic Properties Relevant to Astronomical and Laboratory Detection of MCH and MCH+ (M = Al, Mg)

Abstract New spectroscopic parameters have been calculated to aid in the laboratory and observational detection of AlCH, AlCH+, MgCH, MgCH+, and their deuterated analogs. All species exist in linear geometry except for AlCH+, which exhibits a bent structure. Rotational frequencies have been calculated and the transition with maximum intensity is discussed for three temperature regions present in space: 100 K for a central circumstellar envelope (CSE), 30 K for an outer CSE, and 3 K indicative of the interstellar medium. Pertinent frequencies range from 25 to 250 GHz, depending on the species. At 30 K, the most intense transition is expected to be J = 4 → 3 for all species. The vibrational spectrum of each molecule is expected to be complicated due to the flat nature of the potential energy surface along the bending angle and the presence of anharmonic resonances. Deuteration produces a decrease in vibrational frequency, which may be utilized in experiments to confirm detection of these molecules. The electronic absorption spectrum of both AlCH and MgCH is predicted to be congested and broad. Various high-oscillator-strength transitions are predicted. Upon photoexcitation in the 220–300 nm region, facile dissociation on a repulsive excited state along the Al–C coordinate is predicted to be a source of Al in the colder regions of space. Photodissociation of MgCH requires several nonradiative processes that will control the product state distribution of the fragments.