Including Branching Ratios Research Articles

Blue-excited red emission of CeO2:Eu3+, Al3+ cubic phosphor: Influence of Al3+ ion doping and Judd-Ofelt theory

In this work, a series of CeO2: 0.1 Eu3+, xAl3+ (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mol %) red phosphors could be efficiently excited with blue-light was successfully prepared by solid-state reaction. The X-ray diffraction confirmed the formation of a single-phase CeO2 cubic with high crystallinity. Under blue light (466 nm) excitation, the CeO2: Eu, Al phosphors showed dominant red emission of Eu3+ ions associated with 5D0 – 7F2 transition, which matched well with the commercial blue light InGaN chip. Significantly, the red emission intensity of sample co-doped with 0.3% mol Al3+ was enhanced by 8-times compared to the un-doped one. This result was caused by the presence of Al3+ ions forming oxygen vacancies and disturbing the symmetry of the host, leading to effectively enhanced red emission of the system. The enhanced red emission mechanism of the CeO2:Eu3+, Al3+ phosphors was further explained by Judd-Ofelt (J-O) theory analysis and radiative properties, including branching ratios (βr), transition probability (A), radiative lifetime (τcal), and stimulated emission cross-section (σe) of the phosphor were determined. The CeO2:0.1Eu3+, 0.3Al3+ phosphor shows intense red emission, a long lifetime (0.735 ms), and high quantum efficiency (49.46%), making it a suitable candidate as a red component for preparing low-cost WLEDs.

Experimental and theoretical studies of red emission enhancing mechanism in Al-doped CaMoO4:Eu phosphor

In this work, a complete picture of the relationship between the structural and optical properties of Al-doped CaMoO4:Eu phosphor was investigated empirically and theoretically. A series of Al-doped CaMoO4:Eu phosphors were synthesized by solid-state reaction. X-ray diffraction analysis and Rietveld refinement confirmed the formation of a single-phase tetragonal CaMoO4. Under the excitation wavelength of 395 nm, the phosphors exhibited typical red emission bands of Eu3+ as a function of Al3+ doping contents and reached a maximum value at 0.1 mol % Al3+. In addition, the CaMoO4:0.05Eu, 0.1Al phosphor showed chromaticity coordinates (0.6406, 0.3370), which is close to the pure red color as standardized by the National Television System Committee. Significantly, the red emission intensity of Al-doped CaMoO4: 0.05Eu phosphor was 5-times higher than that of the undoped one. This enhancement was explained by Judd-Ofelt (JO) analysis, from which intensity parameters (Ωλ, λ = 2, 4) and radiative properties including branching ratios (βr), transition probability (A), radiative lifetime (τcal), and stimulated emission cross-section (σe) of the phosphor were derived. Judd-Ofelt analysis confirmed that Al3+ promotes the covalent character in the Eu–O bond and the asymmetry in the CaMoO4 crystalline structure. The CaMoO4: 0.05Eu, 0.1Al phosphor generates strong red emission and possesses high values of branching ratio (81.80%), emission cross-section (102.3×10−22 cm2) and quantum efficiency (48.44%) and is potential for low-cost WLED applications.

Titania nanoparticles embedded Er3+-Sm3+ co-doped sulfophosphate glass: Judd-Ofelt parameters and spectroscopic properties enhancement

The conventional melt quenching method was used to synthesis erbium and samarium ions co-doped sulfophosphate glasses containing TiO2 nanoparticles with the molar compositions of (58.0-x)P2O5-20.0MgO-20.0ZnSO4-1.0Sm2O3-1.0Er2O3-xTiO2 with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mol%. The X-ray diffraction (XRD) technique was applied to verify that the nature of fabricated glass samples is of amorphous type. Judd-Ofelt (JO) intensity (Ωi) parameters were determined through spectral data provided in the investigations conducted on the optical absorption. The applied JO parameterization illustrates the covalency related to rare-earth (RE) ions and ligands. For some given lasing levels, the radiative parameters were estimated including branching ratios (βR), radiative lifetimes (τR), and radiative transition probabilities (A). The photoluminescence spectra provided in some studies are used to evaluate the stimulated emission cross-sections (σpE) for some important lasing transitions including 4G5/2→6H5/2, 4G5/2→6H7/2, and 4G5/2→6H9/2. The determined radiative parameters are potential options as a candidate for lasing.

Luminescence of Phosphate Glasses: P2O5-ZnO-BaF2-K2TeO3-Al2O3-Nb2O5 Doped with Sm3+ Ions for Display and Laser Material

Luminescent phosphate glasses having the composition 40P2O5-30ZnO-20BaF2-3.8K2TeO3-1.2Al2O3-5Nb2O5 in mol.% doped with 3 × 103 ppm and 4 × 103 ppm Sm2O3 were successfully prepared by a melt-quenching technique. The investigated glasses were characterized by x-ray diffraction, UV–visible–NIR, absorption, emission, and fluorescence lifetime analysis. The radiative properties were calculated using Judd–Ofelt (J–O) spectral intensity parameters for each of the glasses, which revealed the following trend: Ω2 > Ω4 > Ω6. The J–O intensity parameters were used to evaluate the spontaneous emission properties including branching ratios, transition probabilities, and radiative lifetime. The value of the optical energy band gap was found to decrease with an increase in Sm3+ content, which is explained on the basis of structural changes. The calculated stimulated emission cross-section $$ \sigma_{\rm{SE}} , $$ at 1.62 μm of glasses studied was high, and increased from 3.81 × 10−21 cm2 to 4.38 × 10−21 cm2 with increasing Sm3+ ion concentration. The structure of the glasses was investigated by computing $$ {\hbox{Internuclear }}\,\left( {r_{\rm{i}} } \right) $$ , Polaron radius $$ \left( {r_{\rm{p}} } \right) $$ and field strength $$ \left( F \right) $$ and measurement of Raman spectra.

Making Sense of Coulomb Explosion Imaging.

A multifaceted agreement between ab initio theoretical predictions and experimental measurements, including branching ratios, channel-specific kinetic energy release, and three-body momentum correlation spectra, leads to the identification of new mechanisms in Coulomb-explosion (CE) induced two- and three-body breakup processes in methanol. These identified mechanisms include direct nonadiabatic Coulomb explosion responsible for CO bond-breaking, a long-range " inverse harpooning" dominating the production of H2+ + HCOH+, a transient proton migration leading to surprising energy partitioning in three-body fragmentation and other complex dynamics forming products such as H2O+ and H3+. These mechanisms provide general concepts that should be useful for analyzing future time-resolved Coulomb explosion imaging of methanol as well as other molecular systems. These advances are enabled by a combination of recently developed experimental and computational techniques, using weak ultrafast EUV pulses to initiate the CE and a high-level quantum chemistry approach to follow the resulting field-free nonadiabatic molecular dynamics.

Monte Carlo simulation of chemistry following radiolysis with TOPAS-nBio

Simulation of water radiolysis and the subsequent chemistry provides important information on the effect of ionizing radiation on biological material. The Geant4 Monte Carlo toolkit has added chemical processes via the Geant4-DNA project. The TOPAS tool simplifies the modeling of complex radiotherapy applications with Geant4 without requiring advanced computational skills, extending the pool of users. Thus, a new extension to TOPAS, TOPAS-nBio, is under development to facilitate the configuration of track-structure simulations as well as water radiolysis simulations with Geant4-DNA for radiobiological studies. In this work, radiolysis simulations were implemented in TOPAS-nBio. Users may now easily add chemical species and their reactions, and set parameters including branching ratios, dissociation schemes, diffusion coefficients, and reaction rates. In addition, parameters for the chemical stage were re-evaluated and updated from those used by default in Geant4-DNA to improve the accuracy of chemical yields. Simulation results of time-dependent and LET-dependent primary yields Gx (chemical species per 100 eV deposited) produced at neutral pH and 25 °C by short track-segments of charged particles were compared to published measurements. The LET range was 0.05–230 keV µm−1. The calculated Gx values for electrons satisfied the material balance equation within 0.3%, similar for protons albeit with long calculation time. A smaller geometry was used to speed up proton and alpha simulations, with an acceptable difference in the balance equation of 1.3%. Available experimental data of time-dependent G-values for agreed with simulated results within 7% ± 8% over the entire time range; for over the full time range within 3% ± 4%; for H2O2 from 49% ± 7% at earliest stages and 3% ± 12% at saturation. For the LET-dependent Gx, the mean ratios to the experimental data were 1.11 ± 0.98, 1.21 ± 1.11, 1.05 ± 0.52, 1.23 ± 0.59 and 1.49 ± 0.63 (1 standard deviation) for , , H2, H2O2 and , respectively. In conclusion, radiolysis and subsequent chemistry with Geant4-DNA has been successfully incorporated in TOPAS-nBio. Results are in reasonable agreement with published measured and simulated data.

Electron-impact ionization ofW27+

Electron-impact ionization cross sections for ${\mathrm{W}}^{27+}$ are calculated using a semirelativistic configuration-average distorted-wave (CADW) method. Calculations for direct ionization, excitation autoionization, and branching ratios are compared with recent calculations by Jonauskas et al. [Phys. Rev. A 91, 012715 (2015)], who used fully relativistic subconfiguration-average distorted-wave (SCADW) and level-to-level distorted-wave (LLDW) methods. Reasonable agreement is found between the CADW and the recent LLDW calculations for direct ionization of the $4l(l=0\char21{}1,3)$ subshells, but not the $4d$ subshell, and between the CADW and recent SCADW-LLDW calculations for excitation autoionization of the $4l(l=0\char21{}2)$ subshells. Reasonable agreement is also found between the CADW and the recent SCADW calculations, including branching ratios, but both differ from the recent LLDW calculations. Additional CADW calculations are made for excitation autoionization, including branching ratios involving the important $3l(l=1\char21{}2)$ subshells, not examined by Jonauskas et al. [Phys. Rev. A 91, 012715 (2015)].

Near-yrast structure ofN=93neutron-rich lanthanide nuclei

Two neutron-rich N=93 isotones, {sup 155}Sm and {sup 153}Nd, have been studied by delayed gamma-ray and conversion-electron spectroscopy at the Lohengrin mass spectrometer. A half-life of 2.9(5) mus has been measured for the nu5/2{sup +}[642] state at 16.5 keV in {sup 155}Sm. The decay of a 1.17(7)-mus isomer in {sup 153}Nd, at 191.7 keV, has been remeasured and its spin has been reassigned as (5/2){sup +}. This state contains a strong component of the nu5/2{sup +}[642] Nilsson orbital. In addition, a new 1.00(8)-mus isomeric state at 538.6 keV, with a probable nu11/2{sup -}[505] Nilsson configuration, has been observed in {sup 155}Sm. Triple gamma-ray coincidence data from the spontaneous fission of a {sup 252}Cf source placed inside the Gammasphere array were used to extend the collective band on top of the (5/2{sup +}) isomeric state of {sup 153}Nd, and a new band with the same bandhead spin has been observed in {sup 151}Ce. The observation of this new band and an additional new transition in the ground-state band has led us to change the ground-state spin of {sup 151}Ce to (3/2{sup -}). Calculations using the quasiparticle-rotor model successfully reproduce the majority of the features of the gamma decays of these nuclei,more » including branching ratios and isomeric half-lives. Because this model uses a reflection-symmetric core, we conclude that the polarizing effect of the odd particle is responsible for the dipole moment present in the nu5/2{sup +}[642] states of the three nuclei studied and the nu11/2{sup -}[505] level of {sup 155}Sm.« less

Features and Mechanism of Chlorine Anion Emission from Microporous Crystal C12A7-Cl- Surface

Chlorine anion (Cl-) emission from the synthesized microporous crystal surface of C12A7-Cl-(11CaO· 7Al2O3·CaCl2) was observed by time-of-flight mass spectrometry (TOF-MS). We investigated the emission features of C12A7-Cl-(including branching ratios of emission intensity, temperature effect, electric field effect, and apparent activation energy) in detail. The anionic species emitted from the C12A7-Cl-surface were dominant by Clanions (maximum branching ratio of intensity: 98%) while a weak O-anion emission and electron emission were also observed. The emission current densities of the anionic species were significantly enhanced by the increase of sample surface temperature or extraction electric field strength. The apparent activation energies for the Cl-emission decreased from 180.9 to 110.0 kJ·mol-1 as the extraction electric field strength increased from 200 to 1200 V·cm-1. The binding energy between the Cl- anion and the C12A7-Cl -surface was about 228 kJ·mol-1. The stability of the Cl- emission was also investigated and an electrochemistry implantation method was adopted to obtain a sustainable Cl-emission. We also discussed the formation and emission mechanism of Cl- anions based on the above investigations. This method may be potentially useful to develop a reservoir or generator of Cl- anions.

Characteristics and Mechanism of Atomic Fluorine Anions Emission from Nanoporous Crystal [Ca24Al28O64]4+·(F−)3.36(O2−)0.32Surface

Atomic fluorine anion (F−) emission from the nanoporous crystal [Ca24Al28O64]4+·(F−)3.36(O2−)0.32 (C12A7-F−) surface, was observed via a time-of-flight mass spectrometry (TOF-MS). C12A7-F− is a nanoporous crystal material with a BET surface area of 1.1 ± 0.1 m2/g. The storage characteristics of C12A7-F−, its emission features (including branching ratios, temperature effect, field effect, apparent activation energy, and emission stability), and its structural alteration after the emission, have been investigated in detail. The anionic species emitted from the C12A7-F− surface were dominant by the F− anions (maximal purity: 96%). A small amount of O− anions and electrons emission were also observed. The emission intensity of F− was significantly enhanced by temperature and the extraction field. The apparent activation energies for the F− emission ranged from 190 to 121 kJ/mol, depending on the extraction field applied. The binding energy between the F− anion and the C12A7-F− surface was about 237 kJ/mol. The anionic species stored in C12A7-F− was dominant by the F− anions ((1.96 ± 0.25) × 1021 cm23) based on ion chromatography, electron paramagnetic resonance. The formation and emission mechanism for the F− anion was discussed based on the above investigations.

Quasi two-step dissociation effects observed in the core excited OCS molecule

Studies of the decay dynamics following carbon 1s and sulfur 2p electron excitations of the OCS molecule using the photoelectron–photoion–photoion coincidence method and a synchrotron radiation source are presented. A Monte Carlo code is utilized to interpret the data obtained, which together with previous measurements including branching ratios, kinetic energy distributions and ionic β-parameters give new information on the dynamics of three-body dissociation processes. The results indicate that the instantaneous and sequential dissociation models should be replaced by quasi two-step models.

CmHn+ Reactions with H and H2: An Experimental Study

We report measurements of the reactions of a number of hydrocarbon ions with atomic and molecular hydrogen made using a selected ion flow tube (SIFT) operating at room temperature. Results, including branching ratios and rate coefficients, are reported for CmHn+ ions (m = 2−6, n = 0−9). Highly unsaturated hydrocarbon ions undergo mainly H atom abstraction reactions with H2 forming CmHn+1+ + H products. More saturated ions are unreactive. Two types of reactions occur for H atoms: H atom transfer to give CmHn-1+ + H2 (if exothermic) and association (to give CmHn+1+).

Exclusive hadronic B decays to charm and charmonium final states.

We have fully reconstructed decays of both B0 and B- Mesons into final states containing either D, D*, D**, Psi, Psi', or Chi_{c1} mesons. This allows us to obtain new results on many physics topics including branching ratios, tests of the factorization hypothesis, color suppression, resonant substructure, and the B- - B0 mass difference.

Levels ofGa69andGa71via the (n, n′γ) Reactions

Differential cross sections for the production of $\ensuremath{\gamma}$ rays in the $\mathrm{Ga}(n, {n}^{\ensuremath{'}}\ensuremath{\gamma})$ reactions have been measured at 90\ifmmode^\circ\else\textdegree\fi{} as a function of incident energy for $0.4\ensuremath{\le}{E}_{n}\ensuremath{\le}2.5$ MeV. Angular distributions at ${E}_{n}=0.650, 0.800, 1.50, \mathrm{and} 1.78$ MeV have also been measured. Level schemes and decay schemes including branching ratios have been determined. An earlier scheme for $^{69}\mathrm{Ga}$ is confirmed, and two new levels are found. The level scheme of $^{71}\mathrm{Ga}$ is defined for excitation energies below 2 MeV. From the $\ensuremath{\gamma}$-ray angular distributions and neutron inelastic scattering cross sections, spins have been determined for five levels in each isotope. When these and other measurements are combined, the following excitation energies in keV, spins, and parities result. In $^{69}\mathrm{Ga}$: 319(${\mathrm{\textonehalf{}}}^{\ensuremath{-}}$), $573({\frac{5}{2}}^{\ensuremath{-}})$, $873({\frac{3}{2}}^{\ensuremath{-}})$, 1027, $1108(\ensuremath{\le}\frac{5}{2})$ $1334(\frac{7}{2})$, 1527, 1724, and 1893. In $^{71}\mathrm{Ga}$: 390(${\mathrm{\textonehalf{}}}^{\ensuremath{-}}$), $487({\frac{5}{2}}^{\ensuremath{-}})$, $512({\frac{3}{2}}^{\ensuremath{-}})$, $911({\frac{1}{2}}^{\ensuremath{-}}, {\frac{3}{2}}^{\ensuremath{-}})$, $965(\frac{7}{2})$, $1108({\frac{7}{2}}^{\ensuremath{-}})$, 1474, 1487, $1495({\frac{9}{2}}^{+})$, 1700, and 1750.