Radiative Decay Lifetime Research Articles

Prediction of mid-infrared 2.72 μm lasing in heavily Er3+-doped fluorotellurite glass

Fluorotellurite glasses heavily doped with Er3+ are prepared in less demanding conditions as compared with fluoride glasses. Specifically, the effects of PbF2 added in the system of AlF3–MgF2–CaF2–SrF2–BaF2–TeO2 (AMCSBYT) are systematically studied on the correlation between glass structure and mid-infrared (MIR) luminescent properties of Er3+. These PbF2-modified glasses with an improved thermal stability and a noticeably reduced phonon energy as compared with telluride glasses exhibit an intense MIR emission at 2.72 μm and a long radiative decay lifetime. Calculation and analysis based on the Judd-Ofelt theory provide deeper insights into the interdependence of luminescent properties and glass structure. Numerical simulation is conducted for a MIR fiber laser based on the experimental data derived from the proposed glass. The 2.72 μm lasing output of 0.68 W is predicted with a slope efficiency of 3.38 %. It is expected that the performance of the fiber laser can be further optimized such that the output power can be increased over 1.0 W. The results emphasize the potential of the PbF2-modified fluorotellurite glass as a promising gain material for 2.72 μm fiber lasers.

Electroluminescence and hyperphosphorescence from stable blue Ir(III) carbene complexes with suppressed efficiency roll-off

Efficient Förster energy transfer from a phosphorescent sensitizer to a thermally activated delayed fluorescent terminal emitter constitutes a potential solution for achieving superb blue emissive organic light-emitting diodes, which are urgently needed for high-performance displays. Herein, we report the design of four Ir(III) metal complexes, f-ct1a ‒ d, that exhibit efficient true-blue emissions and fast radiative decay lifetimes. More importantly, they also undergo facile isomerization in the presence of catalysts (sodium acetate and p-toluenesulfonic acid) at elevated temperature and, hence, allow for the mass production of either emitter without decomposition. In this work, the resulting hyper-OLED exhibits a true-blue color (Commission Internationale de I’Eclairage coordinate CIEy = 0.11), a full width at half maximum of 18 nm, a maximum external quantum efficiency of 35.5% and a high external quantum efficiency 20.3% at 5000 cd m‒2, paving the way for innovative blue OLED technology.

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core-Shell In1-xGaxP/ZnS Colloidal Quantum Dots.

Semiconductors are commonly divided into materials with direct or indirect band gaps based on the relative positions of the top of the valence band and the bottom of the conduction band in crystal momentum (k) space. It has, however, been debated if k is a useful quantum number to describe the band structure in quantum-confined nanocrystalline systems, which blur the distinction between direct and indirect gap semiconductors. In bulk III-V semiconductor alloys like In1-xGaxP, the band structure can be tuned continuously from the direct- to indirect-gap by changing the value of x. The effect of strong quantum confinement on the direct-to-indirect transition in this system has yet to be established because high-quality colloidal nanocrystal samples have remained inaccessible. Herein, we report one of the first systematic studies of ternary III-V nanocrystals by utilizing an optimized molten-salt In-to-Ga cation exchange protocol to yield bright In1-xGaxP/ZnS core-shell particles with photoluminescence quantum yields exceeding 80%. We performed two-dimensional solid-state NMR studies to assess the alloy homogeneity and the extent of surface oxidation in In1-xGaxP cores. The radiative decay lifetime for In1-xGaxP/ZnS monotonically increases with higher gallium content. Transient absorption studies on In1-xGaxP/ZnS nanocrystals demonstrate signatures of direct- and indirect-like behavior based on the presence or absence, respectively, of excitonic bleach features. Atomistic electronic structure calculations based on the semi-empirical pseudopotential model are used to calculate absorption spectra and radiative lifetimes and evaluate band-edge degeneracy; the resulting calculated electronic properties are consistent with experimental observations. By studying photoluminescence characteristics at elevated temperatures, we demonstrate that a reduced lattice mismatch at the III-V/II-VI core-shell interface can enhance the thermal stability of emission. These insights establish cation exchange in molten inorganic salts as a viable synthetic route to nontoxic, high-quality In1-xGaxP/ZnS QD emitters with desirable optoelectronic properties.

Supratransmission-induced traveling breathers in long Josephson junctions

The emergence of traveling sine-Gordon breathers due to the nonlinear supratransmission effect is theoretically studied in a long Josephson junction driven by suitable magnetic pulses, taking into account the presence of dissipation, a current bias, and a thermal noise source. The simulations clearly indicate that, depending on the pulse’s shape and the values of the main system parameters, such a configuration can effectively yield breather excitations only. Furthermore, a nonmonotonic behavior of the breather-only generation probability is observed as a function of the noise intensity. Finally, the dynamics of the supratransmission-induced breathers is characterized by looking at quantities such as their radiative decay lifetime and the medium’s energy.

Excitonic characteristics of blue-emitting quantum dot materials in group II-VI using hybrid time-dependent density functional theory

Colloidal quantum dots (QDs) of group II-VI are key ingredients of next-generation QD light-emitting diodes technology for display and lighting, yet the understanding of their luminescent characteristics are far from being mature. Using a hybrid time-dependent density functional theory, we have studied the electronic and excitonic properties of blue-emitting colloidal QDs within group II-VI containing a thousand atoms or more, including CdSe, CdS, ZnSe, and ZnS QDs, considering both quantum confinement and surface ligand effects. It is found that the calculated optical gaps are in excellent quantitative agreement with experiment, irrespective of the QD nature. Scaling laws of size-dependent energy gaps governed solely by quantum confinement effects have further been explored at both single-particle level and correlated excitonic level for all QDs. With concurrently stoichiometric control and enhancing quantum confinement effects, we have predicted an unusual switching of symmetry character of the highest occupied molecular orbital state from a ${\mathrm{\ensuremath{\Gamma}}}_{3}$ to a ${\mathrm{\ensuremath{\Gamma}}}_{1}$ symmetry at ultrasmall size ($\ensuremath{\sim}1$ nm) for all QDs. After the switching, pronounced linearly polarized band-edge excitonic emission is activated. The radiative exciton decay lifetime is found to increase monotonically with increasing the QD size and tends to saturate at larger sizes. Finally, we have explored the surface passivation mechanism of inorganic chloride ligand, and identified various favorable Cd-Cl bonding configurations which enable an effective surface passivation resembling the commonly applied pseudohydrogen passivation scheme. We find that chloride ligand serves as a hole delocalization ligand and tends to redshift the absorption spectra, reduce the absorption intensity, and significantly enhance the exciton decay lifetime. Our results provide a guideline for spectroscopic studies of excitonic characteristics of colloidal QDs within group II-VI.

High Performance NIR OLEDs with Low Efficiency Roll‐Off by Leveraging Os(II) Phosphors and Exciplex Co‐Host

AbstractNear‐infrared (NIR) organic‐light emitting devices (OLEDs) with high radiance are useful for applications including invisible marking, communication, and biomedical imaging. However, performances of NIR OLEDs are typically limited by their severe efficiency roll‐offs at high current density. Herein, three isoquinolinyl azolate based Os(II) complexes (Isq‐1–3) with short radiative decay lifetime (in hundreds of ns), and photoluminescence with peak wavelengths > 745 nm and quantum yield up to 48% as doped thin films, are reported. Upon concomitant employment of exciplex‐forming co‐host (tris(4‐carbazoyl‐9‐ylphenyl)amine and 2,4,6‐tris(biphenyl‐3‐yl)‐1,3,5‐triazine), efficiency roll‐off is greatly reduced, giving external quantum efficiency of 9.66% at a current density of 300 mA cm−2. A maximum radiance over 170 W sr−1 m−2 is also achieved in devices based on Isq‐2 and Isq‐3.

Compositional dependence of the luminescence properties of Nd3+ ions in lead phosphate glasses: The efficient laser active materials

Spectroscopic investigations on 1 mol% Nd3+ embedded xPbO + (100-x) P2O5 (where x = 40, 50, and 60 mol %) glasses have been reported. Adopting a free-ion Hamiltonian, the energy values and the free-ion parameters are determined. Judd-Ofelt intensity parameters (Ω2, Ω4, Ω6) of Nd3+ ions in lead phosphate glasses are evaluated. Symmetry and covalency of Nd3+ ions are studied with increasing PbO contents in the host glasses. Strong emission due to 4F3/2 → 4I11/2 transition at 1055 nm in the near infrared (NIR) region is observed in the glasses upon excitation at 585 nm. Using the Judd-Ofelt intensity parameters, the radiative transition probability (AR), branching ratio (βR), radiative decay lifetime (τR), stimulated emission cross-section (σP), optical gain parameter and gain bandwidth are calculated for the 4F3/2 metastable state of Nd3+ ion. The luminescence lifetimes are estimated from the decay profiles. Various luminescence parameters for 4F3/2 → 4IJ (J = 9/2, 11/2 and 13/2) transitions are compared with some commercially available Neodymium doped phosphate-based laser glasses. Our investigation indicates that the present glasses could be utilized as the more efficient laser active materials for emission in the NIR region at 1055 nm.

Controlling the triplet states and their application in external stimuli-responsive triplet–triplet-annihilation photon upconversion: from the perspective of excited state photochemistry

The property of organic light-responsive materials is determined by their electronic excited states to a large extent, for instance, the radiative decay rate constants, redox potentials, and lifetimes. Tuning the excited state properties with external stimuli will lead to versatile functional materials; a representative example is the fluorescence molecular probes, in which the singlet excited states are controlled by the external stimuli, i.e., by interaction with the analytes. In comparison, controlling the triplet excited state with external stimuli has been rarely reported, although it is also crucial for the development of novel materials for targeted photodynamic therapy (PDT) reagents and phosphorescent molecular probes. The reported results show that the principles used in singlet excited state tuning are unable to be simply applied to the triplet excited state. In this review article, we summarized the recent results on controlling the triplet excited states by the external stimuli (chemical or light), and the application of the triplet state tuning in the chemical/light controllable triplet-triplet-annihilation upconversion (TTA UC). We discussed the methods for the control of the triplet states, as well as singlet excited state, for the purpose of controlling the TTA UC. Both successful and unsuccessful methods are discussed. This information is helpful for understanding the photophysical processes in which the triplet excited state is involved, and the development of novel external stimuli-responsive triplet photosensitizers.

An Insight into the Excitation States of Small Molecular Semiconductor Y6.

Y6 is a new type of non-fullerene acceptor, which has led to power conversion efficiencies of single-junction polymer solar cells over 17% when combined with a careful choice of polymeric donors. However, the excited state characteristics of Y6, which is closely correlated with its opto-electronic applications, are not clear yet. In this work, we studied the excited state properties of the Y6 solution and Y6 film, by using steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. UV-Vis absorption and fluorescence simulation, natural transition orbitals (NTOs) and hole-electron distribution analysis of Y6 solution were performed for understanding the excitation properties of Y6 by using TD-DFT calculations. The lifetimes of the lowest singlet excited state in Y6 solution and film were estimated to be 0.98 and 0.8 ns, respectively. Combining the exciton lifetime and photoluminescence (PL) quantum yield, the intrinsic radiative decay lifetimes of Y6 in the solution and film were estimated, which were 1.3 and 10.5 ns for the Y6 solution and film, respectively. Long exciton lifetime (~0.8 ns) and intrinsic radiative decay lifetime (~10.5 ns) of Y6 film enable Y6 to be a good acceptor material for the application of polymer solar cells.

Excitons in InP, GaP, and GaxIn1−xP quantum dots: Insights from time-dependent density functional theory

Colloidal quantum dots (QDs) of group III-V are considered as promising candidates for next-generation environmentally friendly light emitting devices, yet there appears to be only limited understanding of the underlying electronic and excitonic properties. Using large-scale density functional theory with the hybrid B3LYP functional solving the single-particle states and time-dependent density functional theory accounting for the many-body excitonic effects, we have identified the structural, electronic and excitonic optical properties of InP, GaP and GaInP QDs containing up to a thousand atoms or more. The calculated optical gap of InP QD appears in excellent agreement with available experiments, and it scales nearly linearly with the inverse diameter. The radiative exciton decay lifetime is found to increase surprisingly linearly with increasing the dot size. For GaP QDs, we predict an unusual electronic state crossover at diameter around 1.5 nm whereby the nature of the lowest unoccupied molecular orbital (LUMO) state switches its symmetry from $\Gamma_{5}$-like at larger diameter to $\Gamma_{1}$-like at smaller diameter. After the crossover, the absorption intensity of the band-edge exciton states is significantly enhanced. Finally, we find that Vegard's law holds very well for GaInP random alloyed quantum dots down to ultra-small sizes with less than a hundred atoms. The obtained energy gap bowing parameter of this common-cation compound in QD regime appears positive, size-dependent and much smaller than its bulk parentage. The volume deformation, dominating over the charge exchange and structure relaxation effects, is mainly responsible for the QD energy gap bowing. The present work provides a road map for a variety of electronic and optical properties of colloidal QDs in group III-V that can guide spectroscopic studies.

Luminescence and Electron Dynamics in Atomically Precise Nanoclusters with Eight Superatomic Electrons.

The [Au25(SR)18]- and [Au13(dppe)5Cl2]3+ [dppe = 1,2-bis(diphenylphosphino)ethane] nanoclusters both possess a 13-atom icosahedral core with 8 delocalized superatomic electrons (8e), but their emission properties and time-resolved electron dynamics differ significantly. In this work, experimental photoluminescence and photoluminescence decay measurements are combined with time-dependent density functional theory calculations of radiative and nonradiative decay properties and lifetimes to elucidate the similarities and differences in the emission of these two nanoclusters with similar cores. In this work, the photodynamic properties of [Au13(dppe)5Cl2]3+ are elucidated theoretically for the first time. [Au13(dppe)5Cl2]3+ exhibits a single strong emission peak compared to the weaker bimodal luminescence of [Au25(SR)18]- (modeled here as [Au25(SH)18]-). The strongly emissive state is found to arise from deexcitation out of the S1 state, similar to what is seen for [Au25(SH)18]-. Both theory and experiment exhibit microsecond lifetimes for this state. Transient absorption measurements and theoretical calculations demonstrate that the excited-state lifetimes for higher excited states are typically less than 1 ps. The decay times for the higher excited states of [Au13(dppe)5Cl2]3+ and its model compound [Au13(pe)5Cl2]3+ [pe = 1,2-bis(phosphino)ethane] are observed to be shorter than the lifetimes of the corresponding states of [Au25(SR)18]-; this occurs because the energy gap separating degenerate sets of unoccupied orbitals is only ∼0.2 eV in [Au13(dppe)5Cl2]3+ compared to a ∼0.6 eV energy gap in [Au25(SH)18]-.

Energy levels, oscillator strengths, radiative transition probabilities, level lifetimes and electron-impact excitation rate coefficients for Ne-like Mo XXXIII

The energy levels, oscillator strengths, radiative decay rates, lifetimes, collision strengths, direct and resonance electron-impact excitation rate coefficients have been computed for the 257 fine-structure levels arising from 1s22s22p5nl and 1s22s2p6n′l′ configurations belonging to the Mo32+ ion with n≤7, l≤4 and n′≤5, l′≤4. The model-potential approach is used for the target ion structure calculations. Additionally, we employ the multiconfiguration Dirac–Hartree–Fock method to further assess the energy levels and transition probabilities. The collision strengths for the electron-impact direct excitation are computed within the relativistic distorted-wave approximation at 34, 135, 680, 1700, 5436, and 12,740 eV scattered electron energy values. We also perform collision calculations at 85, 175, and 450 keV electron energies using the plane-wave approximation and interpolate the reduced cross section within Fano plots, thus accounting for relativistic effects at asymptotic energies. This assures the convergence of Maxwellian integration for effective collision strengths calculation at electron temperatures up to 80 keV. The resonance contribution to the excitation rates is accounted for within the independent process isolated resonance approximation by including Na-like Mo31+ doubly excited autoionization states arising from the 1s227nln′l′ configurations with n≤7,l≤4,n′≤20,l′≤8. Contributions from high n′≥21 Rydberg states to the excitation rate coefficients are included by employing the n′−3 extrapolation law for radiative and autoionization decay rates. Radiative decay of resonances to lower autoionization states followed by autoionization cascade as well as radiative damping via core transitions are included in our model. The highest rate coefficients corresponding to ground state excitations are the 2p–3d allowed and 2p–3p electric monopole transitions, respectively. Intercombination and generally higher-order electric multipole transitions amount to lower excitation rate coefficients but are not to be neglected. Magnetic transitions are only relevant for low electron temperatures since both their direct and resonance contributions to excitation significantly decrease with increasing electron energy. Present results compare well with existing data from literature. The resonance contributions play an important role in the accuracy of rate coefficients, especially for weak forbidden transitions at low electron temperatures. These results may be useful in fusion related plasmas, astrophysics and fundamental physics.

Effect of annealing temperature on spectroscopic features and photocatalytic activity of TiO2:0.07Eu3+ nanoparticles

TiO2:0.07Eu3+ thin films were deposited by sol-gel spin coating technique and the effect of annealing temperature on photocatalytic activity (PCA) and red-light emission efficiency was studied. The crystalline structure and phase formation of TiO2:0.07Eu3+ nanophosphors were identified by x-ray diffraction analysis. These results confirm the formation of a single anatase phase for the above films. The HR-TEM images of TiO2:0.07Eu3+ thin film has revealed that all the particles have spherical in shape with an average particle size of 8 nm. From Raman analysis, it is found that the phase formation and modes of vibrations present in TiO2:0.07Eu3+ thin films. The films showed a significant red-shift in band edge with annealing temperatures. The phonon energy was estimated from the PL excitation spectrum and found good agreement with the Raman modes. At 393 nm excitation, the anatase TiO2:0.07Eu3+ nanophosphors exhibited strong PL emission due to f–f transitions of Eu3+ and the dominant red emission was the hypersensitive 5D0 → 7F2 transition. The intensity of luminescence emission was found to increase with an increase in annealing temperatures. Radiative transition rates, fluorescence branching ratio, stimulated emission cross section and radiative decay lifetime was resolved with Judd-Ofelt analysis. The chromaticity coordinate values (0.644, 0.350) were estimated using the CIE-1931 system, which is near to the NTSC red phosphor chromaticity coordinate values. The photo-degradation efficiencies of TiO2:0.07Eu3+ thin films were found to improve with an increase in annealing temperatures. TiO2:0.07Eu3+ film annealed at 550 °C displays high PCA than other films for the degradation of Methylene Blue (MB) under visible light illumination.

Lifetime of the metastable P1/22 state of F-like Ar9+ isolated in a compact Penning trap

Multiply ionized atoms of a single charge state can be captured at low energy in a compact Penning trap, allowing the measurement of the radiative lifetime of an atomic state that decays via weakly allowed transitions. Such a measurement is reported here for the radiative decay lifetime of the metastable $^{2}P_{1/2}$ state in fluorinelike ${\mathrm{Ar}}^{9+}$, wherein the $n=2$ shell has only one vacancy (hole) in a $2p$ orbital. Highly ionized atoms are extracted from an electron beam ion trap and guided into the ion capture apparatus. Upon capturing the ${\mathrm{Ar}}^{9+}$ ions, light from the magnetic-dipole transition is detected with a photomultiplier tube and counted with a multichannel scaler. Using this technique, the radiative lifetime of the metastable $^{2}P_{1/2}$ state in ${\mathrm{Ar}}^{9+}\phantom{\rule{4pt}{0ex}}1{s}^{2}\phantom{\rule{0.16em}{0ex}}2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{5}$ is measured to be $\ensuremath{\tau}=9.31\ifmmode\pm\else\textpm\fi{}0.08$ ms, consistent with a previous intra-EBIT measurement.

Blue-emitting bis-tridentate Ir(iii) phosphors: OLED performances vs. substituent effects

Dependence of external quantum efficiency (EQE) and radiative decay lifetime of blue-emitting OLED is established with photostable, bis-tridentate Ir(iii) emitters, giving max. EQE and luminescence of 12.2% and 18 980 cd m−2, and with CIEx,y coordinates between (0.16, 0.22) and (0.17, 0.27).

Study of recombination characteristics in MOCVD grown GaN epi-layers on Si

The radiative and non-radiative recombination carrier decay lifetimes in GaN epi-layers grown by metal-organic chemical vapour deposition technology on Si substrates were measured by contactless techniques of time-resolved photoluminescence and microwave-probed transients of photoconductivity. The lifetime variations were obtained to be dependent on growth regimes. These variations have been related to varied densities of edge dislocations associated with growth temperature. It has been also revealed that the lateral carrier lifetime and photoluminescence intensity distribution is determined by the formation of dislocation clusters dependent on the growth conditions. For low excitation level, the asymptotic component within the excess carrier decay transients is attributed to carrier trapping and anomalous diffusion through random-walk processes within dislocation cluster regions and barriers at dislocation cores. The two-componential decay process at high excitation conditions, where excess carriers may suppress barriers, proceeds through a nonlinear recombination, where band-to-band transitions determine the nonlinearity of the process, while the asymptotic component is ascribed to the impact of D-A pair PL within the long-wavelength wing of the UV-PL band.

Single-Photon-Emitting Optical Centers in Diamond Fabricated upon Sn Implantation

The fabrication of luminescent defects in single-crystal diamond upon Sn implantation and annealing is reported. The relevant spectral features of the optical centers (emission peaks at 593.5 nm, 620.3 nm, 630.7 nm and 646.7 nm) are attributed to Sn-related defects through the correlation of their photoluminescence (PL) intensity with the implantation fluence. Single Sn-related defects were identified and characterized through the acquisition of their second-order auto-correlation emission functions, by means of Hanbury-Brown-Twiss interferometry. The investigation of their single-photon emission regime as a function of excitation laser power revealed that Sn-related defects are based on three-level systems with a 6 ns radiative decay lifetime. In a fraction of the studied centers, the observation of a blinking PL emission is indicative of the existence of a dark state. Furthermore, absorption dependence from the polarization of the excitation radiation with about 45 percent contrast was measured. This work shed light on the existence of a new optical center associated with a group-IV impurity in diamond, with similar photo-physical properties to the already well-known Si-V and Ge-V emitters, thus providing results of interest from both the fundamental and applicative points of view.

Structural and optical studies of Er3+-doped alkali/alkaline oxide containing zinc boro-aluminosilicate glasses for 1.5 μm optical amplifier applications

In the present work, we report on the optical spectral properties of Er3+-doped zinc boro-aluminosilicate glasses with an addition of 10 mol % alkali/alkaline modifier regarding the fabrication of new optical materials for optical amplifiers. A total of 10 glasses were prepared using melt−quenching technique with the compositions (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO − 10Li2O − xEr2O3 and (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO – 10MgO − xEr2O3 (x = 0.1, 0.25, 0.5, 1.0, and 2.0 mol %). We confirm the amorphous-like structure for all the prepared glasses using X-ray diffraction (XRD). To study the functional groups of the glass composition after the melt−quenching process, Raman spectroscopy was used, and various structural units such as triangular and tetrahedral-borates (BO3 and BO4) have been identified. All the samples were characterized using optical absorption for UV, visible and NIR regions. Judd-Ofelt (JO) intensity parameters (Ωλ, λ = 2, 4 and 6) were calculated from the optical absorption spectra of two glasses LiEr 2.0 and MgEr 2.0 (doped with 2 mol % of Er3+). JO parameters for LiEr 2.0 and MgEr 2.0 glasses follow the trend as Ω6>Ω2>Ω4. Using Judd–Ofelt intensity parameters, we obtained radiative probability A (S−1), branching ratios (β), radiative decay lifetimes τrad (μs) of emissions from excited Er+3 ions in LiEr 2.0 and MgEr 2.0 to all lower levels. Quantum efficiency (η) of 4I13/2 and 4S3/2 levels for LiEr 2.0 and MgEr 2.0 with and without 4D7/2 level was calculated using the radiative decay lifetimes τrad. (μs) and measured lifetimes τexp. (μs). We measured the visible photoluminescence under 377 nm excitation for both LiEr and MgEr glass series within the region 390–580 nm. Three bands were observed in the visible region at 407 nm, 530 nm, and 554 nm, as a result of 2H9/2 → 4I15/2, 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, respectively. Decay lifetimes for emissions at 407 nm, 530 nm, and 554 nm were measured and they show single exponential behavior for all the LiEr and MgEr glass series. From the photoluminescence and radiative decay lifetimes (τrad), we calculated the full-width at half-maximum (FWHM), emission cross-section (σPE) and bandwidth gain (FWHM×σPE) parameters. Near-infrared photoluminescence under 980 nm excitation was measured for all the LiEr and MgEr glass series in the region 1420–1620 nm. NIR emissions show a broadband centered at ∼1530 nm due to the transition of Er3+: 4I13/2 → 4I15/2. Decay lifetimes for NIR emission at ∼1530 nm were measured and they show a quite exponential nature for all the LiEr and MgEr glass series. From the NIR emission spectra and decay lifetimes, we calculated the full-width at half-maximum (FWHM), the emission cross-section (σPE) and the bandwidth gain (FWHM×σPE) for the NIR emission and it shows FWHM of 50–70 nm for prepared glasses, emission cross-section of (∼3.5)× 10−20 cm2, while bandwidth gain was (∼25) × 10−26 cm3.

Atomic data and line intensities for the S V ion

The energy levels, oscillator strengths, spontaneous radiative decay rates, lifetimes and electron impact collision strengths have been obtained for the [Ne]3snl, [Ne]3pnl, [Ne]3dnl configurations belonging to S V ion, with n≤7 and l≤4, resulting in 567 fine-structure levels. The calculations have been performed within the fully relativistic Flexible Atomic Code (FAC, Gu, 2008) framework and the distorted wave approximation. To attain the desired accuracy for the levels energy, the valence–valence and valence–core correlations have been taken care of by including 96 configuration state functions (CSFs) in the model, reaching a total of 3147 fine-structure levels. Two separate calculations have been performed with the local central potential computed for two different average configurations. A third calculation is also performed without the addition of the core-excited states in the atomic model for completeness. The effects of slightly different mean configurations and valence–core correlations on the energy levels and decay rates are investigated. The collision data have been computed employing the relativistic distorted-wave method along with the atomic model containing the 96 CSFs and corresponding to the ground state mean configuration. The collision strengths corresponding to excitation from the first four fine-structure levels are given for five energy values of the scattered electron 2.65, 6.18, 11.02, 17.36, 25.43 Rydberg, plus an additional variable small energy value near the threshold. A collisional-radiative model has been employed to solve the rate equations for the populations of the 567 fine-structure levels, for a temperature of LogTE(K)=5.2 corresponding to the maximum abundance of S V, and at densities 106–1016cm−3, assuming a Maxwellian electron energy distribution function and black body radiation of temperature 6000 K and dilution factor 0.35 for the photon distribution function. The main processes responsible for the level population variations are the electron-impact collisional excitation and the radiative decay along with their inverse processes. As a result, the level populations along with the spectral high-line intensity ratios are provided.

Experiments with Highly-Ionized Atoms in Unitary Penning Traps

Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 1019 level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr17+), as well as for studying electron capture processes.