Spectral Decay Research Articles

A Cerium Doped Scandate Broad Orange-Red Emission Phosphor and its Energy Transfer-Dependent Concentration and Thermal Quenching Character.

A series of BaSr2Sc4O9 and Ce3+-doped BaSr2Sc4O9 phosphors were synthesized via the high temperature solid state reaction. Crystal structure information on BaSr2Sc4O9 is first refined using the Rietveld method based on the XRD data, and it is assigned to the trigonal system with the R3 space-group. The photoluminescence properties were investigated in detail, including the emission and excitation spectra, site occupation, decay lifetime, thermal quenching, and quantum efficiency. There are three Ba2+/Sr2+ sites and four Sc3+ sites in this structure. The Ce3+ ions in the 6-fold coordinated Sr2+/Ba2+ sites show a near-ultraviolet-blue emission with a peak at around 407 nm under ultraviolet excitation. The Ce3+ ions in Sc3+ sites exhibit a bright broad orange-red emission with the peak at around 615 nm under near-ultraviolet and blue excitation. The energy transfer process between the different sites is demonstrated based on the spectral analysis, theoretical calculation, and decay lifetime variation. Under excitation of 345 nm, the energy transfer phenomenon and distribution of activator ions lead to the invalidation of part of the Ce3+ ions, and then it causes a higher concentration quenching point. The participation of the energy transfer in the thermal quenching phenomenon causes the abnormal intensity variation, which is ascribed to the energy compensation by the increasing energy transfer efficiency at high temperature. The internal quantum efficiency is 45% under the 420 nm excitation wavelength. An excellent white light emitting diode lamp is obtained by fabricating BaSr2Sc4O9:Ce3+ with BAM:Eu2+, β-sialon:Eu2+, and a 395 nm GaN chip; its CIE coordinate ( x, y), CCT, and Ra are (0.3708, 3463), 4023 K, and 84. These results reveal the correlation between energy transfer and luminescent property and provide a practical foundation to comprehend and adjust the photoluminescence performance.

Luminescence property, energy transfer and thermal property of color tunable phosphor Ca9-wCe0.5Y0.5-x-y-z(PO4)7:xTb3+, yEu3+, zSm3+, wMn2+

Series of Ca9-wCe0.5Y0.5-x-y-z(PO4)7:xTb3+, yEu3+, zSm3+, wMn2+ phosphors are synthesized by a high temperature solid state method. The spectral property and fluorescence decay curves are measured and used to demonstrate the energy transfer effect in Ce3+-Tb3+, Ce3+-Sm3+, Ce3+-Eu3+, Tb3+-Sm3+, Tb3+-Eu3+ and Tb3+-Mn2+. For Ca9Ce0.5Y0.5(PO4)7, the concentration of Ce3+ is higher and it can act as activator and sensitizer simultaneously. Ce3+ and Tb3+ can emit blue and green light under near ultraviolet excitation, respectively. Sm3+, Eu3+ and Mn2+ can produce red emission. In order to generate white light, Ce3+/Tb3+/Sm3+, Ce3+/Tb3+/Eu3+ and Ce3+/Tb3+/Mn2+ doped phosphors are investigated, and Ca8.8Ce0.5Y0.33(PO4)7:0.17Tb3+,0.20Mn2+ can create high quality white light. Its color rendering index can be high up to 80.2 and correlated color temperature is 4735 K, and its thermal stability is high. The result indicates that the acquired phosphors can be potential for the use of ultraviolet excited white light emitting diodes.

A comparison of refinement indicators for p-adaptive simulations of steady and unsteady flows using discontinuous Galerkin methods

This paper presents an analysis of refinement indicators for the simulation of steady and unsteady flows by means of p-adaptive algorithms for discontinuous Galerkin (DG) methods. Residual-error, discretization-error and feature-based indicators are compared by studying their effect on convergence history, computational gain and refinement regions selected by the adaptive algorithm. The analysis is initially carried out on steady flow configurations. Static p-adaptive simulations of the periodic flow past a cylinder at Re=100 are then performed. Compared to uniform p-refinement, a reduction between 50% and 75% in the number of degrees of freedom is obtained for all test cases considered. The accuracy and efficiency observed for the small-scale energy density [1] and spectral decay [2] indicators demonstrate their great potential for the adaptive simulation of unsteady flows.

Spectral energy cascade and decay in nonlinear acoustic waves

We present a numerical and theoretical investigation of nonlinear spectral energy cascade of decaying finite-amplitude planar acoustic waves in a single-component ideal gas at standard temperature and pressure (STP). We analyze various one-dimensional canonical flow configurations: a propagating traveling wave (TW), a standing wave (SW), and randomly initialized Acoustic Wave Turbulence (AWT). We use shock-resolved mesh-adaptive direct numerical simulations (DNS) of the fully compressible one-dimensional Navier-Stokes equations to simulate the spectral energy cascade in nonlinear acoustic waves. We also derive a new set of nonlinear acoustics equations truncated to second order and the corresponding perturbation energy corollary yielding the expression for a new perturbation energy norm $E^{(2)}$. Its spatial average, <$E^{(2)}$> satisfies the definition of a Lyapunov function, correctly capturing the inviscid (or lossless) broadening of spectral energy in the initial stages of evolution -- analogous to the evolution of kinetic energy during the hydrodynamic break down of three-dimensional coherent vorticity -- resulting in the formation of smaller scales. Upon saturation of the spectral energy cascade i.e. fully broadened energy spectrum, the onset of viscous losses causes a monotonic decay of <$E^{(2)}$> in time.

A mixed generalized multiscale finite element method for planar linear elasticity

A mixed generalized multiscale finite element method for linear elasticity based on Hellinger Reissner principle with a strong symmetry enforcement for the stress tensor is introduced. The multiscale approximation space for the stress tensor is built on a coarse grid with carefully designed local problems so that the basis functions are also symmetric. Using eigenfunctions of local spectral problems as basis functions allows the approximation error of the multiscale finite element space to have a rapid spectral decay. Together with a properly chosen approximation space for the displacement, the method is shown to be inf–sup stable and robust as the first Lamé coefficient λ → ∞ . Numerical experiments are supplemented to demonstrate fast convergence of the method with respect to local enrichment, and robustness of the method with respect to high contrast heterogeneity of the Poisson ratio.

Reconstruction of the glottal pulse using a subband technique on kazoo recordings

The kazoo, a wind instrument, generates its typical sound when stimulated by voiced speech. Using this instrument, this paper proposes a novel technique to recover the glottal pulse excitation of its player. We applied multiband frequency techniques to the kazoo signal to compare the results with those obtained from the corresponding recordings of an electroglottograph (EGG). With the player's management over his embouchure on the instrument, one can make recordings for spoken and singing speech as well as recitative, at the instrument’s resonator cap, which closely fit the EGG recordings. After a spectrogram analysis, it was possible to detect in the lower frequency band of the kazoo signals, the spectral envelope and, in the higher frequency band, the pitch harmonics mixed with the spectral decay of the glottal pulse. A quadrature mirror filter (QMF) was designed, providing this source-filter separation. Additionally, a reverse spectral band replication (SBR) technique was applied, which consists in recovering the lower frequency band by the demodulation of the higher frequency band followed by a total energy spectral gain adjustment, where a new signal was generated and then evaluated. At the end, a subjective evaluation, SNR, and SD measures prove the efficiency of the proposed method.

Analysis of propagation characteristics of a shear wave in a frictionally bonded fibre-reinforced stratum

The present article aims to unravel the propagation characteristics of a shear wave in the context of reinforcement and frictional bonding in a composite structure. The geometrical configuration of the composite structure is comprised with a fibre-reinforced layer and an isotropic homogeneous semi-infinite medium which are frictionally bonded to each other. An analytical technique is employed to find the complex form of the frequency equation which is separated into real and imaginary parts representing the dispersion and damping relation, respectively. As a particular case of the problem, the deduced results are matched with the classical Love equation. The numerical simulation is performed to graphically portray the analytical findings and to trace out the effect of reinforcement by a comparative study which is a major highlight of the study. The significant influence of reinforcement, frictional bonding, and spectral decay parameter on the phase, group, and damped velocities are revealed. The outcome of the present study may be helpful to gain deeper insight into the propagation characteristics of a shear wave in a frictionally bonded composite structure which may provide useful information in engineering applications.

Pulse Cathodoluminescence of the Impurity Centers in Ceramics Based on the MgAl2O4 Spinel

The spectral and luminescence decay kinetics of magnesium aluminate spinel ceramics prepared by spark plasma sintering (SPS) and the starting nanopowders were studied. It was demonstrated that two types of luminescence in spinel ceramics can be observed after pulse e-beam excitation. The first type is due to intrinsic defects, and the second type due to Cr3+ and Mn2+ ions. It was shown that the luminescence decay kinetics for Cr3+ and Mn2+ impurity ions can be approximated by the sum of two exponents. The decay times for the Cr3+ ion are 35 and 409 ns, for the Mn2+ ion are 29 and 340 ns. High-temperature exposure during SPS synthesis does not lead to a change in the nearest surroundings of impurity ions. In the luminescence spectra of ceramic and powder samples the intensity ratio changes of intrinsic and impurity centers is associated with strong diffuse scattering of light for spinel nanopowders.

Regional Variability and Turbulent Characteristics of the Satellite‐sensed Submesoscale Surface Chlorophyll Concentrations

AbstractThe regional variability and turbulent characteristics of submesoscale surface chlorophyll concentrations are examined with hourly maps of geostationary ocean color imagery‐derived chlorophyll concentrations at a 0.5 km resolution for a period of 5 years (2011–2015) over the East/Japan Sea with concurrent mesoscale and submesoscale observations. Two seasonal blooms occur in the spring and fall within 250 km off the coast that are associated with constructive combinations of light exposure, nutrients, and vertical stratification. Another bloom occurs in the summer and is closely related to regional wind‐driven upwelling events. The spring and fall blooms are more significant near the coast (within 40 km from the coast) than offshore because of the more energetic submesoscale horizontal shear and vortical phenomena onshore as well as their propagation in the cross‐shore direction. In addition, the regional spring bloom starts offshore and migrate onshore with a time delay of 1 month, which may result from the onshore propagation of geostrophic currents, the deepening of the mixed layer, and favorable nutrient fluxes from the subsurface. The wavenumber‐domain energy spectra of chlorophyll concentrations exhibit anisotropy, which may be closely related to bathymetric effects and regional circulations. The spectral decay slopes change from to at the O(10) km scales and from to at the O(1) km scales and have weak seasonality. These results are consistent with the two‐dimensional quasi‐geostrophic turbulence theory and can be interpreted with the baroclinic instability energized from the moderate seasonal mixed layer under mesoscale regional circulations.

Estimation and applicability of attenuation characteristics for source parameters and scaling relations in the Garhwal Kumaun Himalaya region, India

Source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process, the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region. In this study, the source parameters were determined for 58 small to moderate size earthquakes (3.0 ≤ Mw ≤ 5.0) occurred during 2007–2015 in the Garhwal-Kumaun region. The estimated shear wave quality factor (Qβ(f)) values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters. The Qβ(f) values have been estimated by using coda wave normalization method in the frequency range 1.5–16 Hz. A frequency-dependent S wave quality factor relation is obtained as Qβ(f) = (152.9 ± 7) f(0.82±0.005) by fitting a power-law frequency dependence model for the estimated values over the whole study region. The spectral (low-frequency spectral level and corner frequency) and source (static stress drop, seismic moment, apparent stress and radiated energy) parameters are obtained assuming ω−2 source model. The displacement spectra are corrected for estimated frequency-dependent attenuation, site effect using spectral decay parameter “Kappa”. The frequency resolution limit was resolved by quantifying the bias in corner frequencies, stress drop and radiated energy estimates due to finite-bandwidth effect. The data of the region shows shallow focused earthquakes with low stress drop. The estimation of Zúñiga parameter (ε) suggests the partial stress drop mechanism in the region. The observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model. Presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region. However, the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth, attenuation and site corrections. Although, the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach.

Exponential Decay of the Lengths of the Spectral Gaps for the Extended Harper’s Model with a Liouvillean Frequency

In this paper, we study the non-self dual extended Harper's model with Liouvillean frequency. By establishing quantitative reducibility results together with the averaging method, we prove that the lengths of spectral gaps decay exponentially.

Kalman filter approach for uncertainty quantification in time-resolved laser-induced incandescence.

Time-resolved laser-induced incandescence (TiRe-LII) data can be used to infer spatially and temporally resolved volume fractions and primary particle size distributions of soot-laden aerosols, but these estimates are corrupted by measurement noise as well as uncertainties in the spectroscopic and heat transfer submodels used to interpret the data. Estimates of the temperature, concentration, and size distribution of soot primary particles within a sample aerosol are typically made by nonlinear regression of modeled spectral incandescence decay, or effective temperature decay, to experimental data. In this work, we employ nonstationary Bayesian estimation techniques to infer aerosol properties from simulated and experimental LII signals, specifically the extended Kalman filter and Schmidt-Kalman filter. These techniques exploit the time-varying nature of both the measurements and the models, and they reveal how uncertainty in the estimates computed from TiRe-LII data evolves over time. Both techniques perform better when compared with standard deterministic estimates; however, we demonstrate that the Schmidt-Kalman filter produces more realistic uncertainty estimates.

Time-resolved laser fluorescence spectroscopy of organic ligands by europium: Fluorescence quenching and lifetime properties

Time-resolved Laser Fluorescence Spectroscopy (TRLFS) has proved its usefulness in the fields of biophysics, life science and geochemistry to characterize the fluorescence probe molecule with its chemical environment. The purpose of this study is to demonstrate the applicability of this powerful technique combined with Steady-State (S-S) measurements. A multi-mode factor analysis, in particular CP/PARAFAC, was used to analyze the interaction between Europium (Eu) and Humic substances (HSs) extracted from Saint Lawrence Estuary in Canada. The Saint Lawrence system is a semi-enclosed water stream with connections to the Atlantic Ocean and is an excellent natural laboratory. CP/PARAFAC applied to fluorescence S-S data allows introspecting ligands–metal interactions and the one-site 1:1 modeling gives information about the stability constants. From the spectral signatures and decay lifetimes data given by TRLFS, one can deduce the fluorescence quenching which modifies the fluorescence and discuss its mechanisms. Results indicated a relatively strong binding ability between europium and humic substances samples (LogK value varies from 3.38 to 5.08 at pH 7.00). Using the Stern-Volmer plot, it has been concluded that static and dynamic quenching takes places in the case of salicylic acid and europium interaction while for HSs interaction only a static quenching is observed.

Preliminary Estimation of Kappa Parameter in Croatia

Spectral parameter kappa κ is used to describe spectral amplitude decay “crash syndrome” at high frequencies. The purpose of this research is to estimate spectral parameter kappa for the first time in Croatia based on small and moderate earthquakes. Recordings of local earthquakes with magnitudes higher than 3, epicentre distances less than 150 km, and focal depths less than 30 km from seismological stations in Croatia are used. The value of kappa was estimated from the acceleration amplitude spectrum of shear waves from the slope of the high-frequency part where the spectrum starts to decay rapidly to a noise floor. Kappa models as a function of a site and distance were derived from a standard linear regression of kappa-distance dependence. Site kappa was determined from the extrapolation of the regression line to a zero distance. The preliminary results of site kappa across Croatia are promising. In this research, these results are compared with local site condition parameters for each station, e.g. shear wave velocity in the upper 30 m from geophysical measurements and with existing global shear wave velocity – site kappa values. Spatial distribution of individual kappa’s is compared with the azimuthal distribution of earthquake epicentres. These results are significant for a couple of reasons: to extend the knowledge of the attenuation of near-surface crust layers of the Dinarides and to provide additional information on the local earthquake parameters for updating seismic hazard maps of studied area. Site kappa can be used in the re-creation, and re-calibration of attenuation of peak horizontal and/or vertical acceleration in the Dinarides area since information on the local site conditions were not included in the previous studies.

Interfacial Engineering with Cross-Linkable Fullerene Derivatives for High-Performance Perovskite Solar Cells.

Two fullerene derivatives with styryl and oxetane cross-linking groups served as interfacial materials to modify an electron-transporting layer (ETL) of TiO2, doped with Au nanoparticles, processed under low-temperature conditions to improve the performance of perovskite solar cells (PSC). The cross-linkable [6,6]-phenyl-C61-butyric styryl dendron ester was produced via thermal treatment at 160 °C for 20 min, whereas the cross-linkable [6,6]-phenyl-C61-butyric oxetane dendron ester (C-PCBOD) was obtained via UV-curing treatment for 45 s. Both cross-linked fullerenes can passivate surface-trap states of TiO2 and have also excellent surface coverage on the TiO2 layer shown in the corresponding atomic force microscopy images. To improve the crystallinity of perovskite, we propose a simple co-solvent method involving mixing dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a specific ratio (DMF/DMSO = 90/10). The fullerene derivative layer between the ETL and perovskite layers significantly improved electron extraction and suppressed charge recombination by decreasing the density of traps at the ETL surface. A planar PSC device was fabricated with the configuration indium tin oxide/TiO2 (Au)/C-PCBOD/perovskite/spiro-OMeTAD/Au to attain a power conversion efficiency (PCE) of 15.9%. The device performance was optimized with C-PCBOD as an interfacial mediate to modify the surface of the mesoporous TiO2 ETL; the C-PCBOD-treated device attained a significantly enhanced performance, PCE 18.3%. Electrochemical impedance spectral and photoluminescence decay measurements were carried out to understand the characteristics of electron transfer and charge recombination of the perovskite/TiO2 samples with and without a fullerene interfacial layer.

Local, Temperature-Dependent Trapping and Detrapping in the LiGa5O8:Cr Infrared Emitting Persistent Phosphor

The near-infrared emitting persistent phosphor LiGa5O8:Cr3+ (LGO:Cr) has promising applications in bioimaging. In order to improve the persistent luminescence of LGO:Cr and other Cr-doped persistent phosphors, a better understanding of trapping and detrapping mechanisms is necessary. In this work, we study the afterglow and thermoluminescence via a thermal fading experiment. The results show that there is a broad trap distribution present in LGO:Cr. The emission spectrum of chromium changes during the afterglow, which indicates that different Cr ions experience a varying crystal field in the LGO host, due to different defect configurations, and that the detrapping process occurs locally. The results of thermoluminescence and spectral decay measurements show that chromium ions residing near deep traps are subject to a smaller crystal field. Vacancies formed during the synthesis are most probably causing this effect. Codoping LGO with Si4+ or Ge4+ significantly improves the persistent luminescence and increases the number of deep-lying traps in the phosphor.

Synthesis, structure and magnetic studies of lanthanide metal–organic frameworks (Ln–MOFs): Aqueous phase highly selective sensors for picric acid as well as the arsenic ion

A series of three lanthanide metal–organic frameworks (Ln–MOFs) consisting of a planar functionalized dicarboxylic acid was synthesized. The Ln–MOFs, with the composition [Ln3(PDC)3Cl3(H2O)]n [Ln = La (1), Nd (2) or Pr (3), PDCH2 = pyridine-2,6-dicarboxylic acid], were characterized employing spectral, time resolved fluorescence, magnetic, single crystal X-ray and PXRD analysis. X-ray crystallography confirms that the structure of the Ln–MOFs is constructed by trinuclear (Ln3) units and the deprotonated PDC2− ligand, which is simplified into a 3-c, uninodal net having the vab topology with the 10^3-point symbol. The variable temperature magnetic susceptibility data indicate that there are antiferromagnetic interactions between LnIII⋯LnIII ions in 2 and 3 with Curie constants of 5.917 (2) and 5.231 (3) cm3 K mol−1, Weiss constants −60.71 (2) and −48.43 (3) K, and zJ′ values −0.98 (2) and −0.31 (3) cm−1. The 3D polymers 1–3 are characterized as being highly selective, sensitive and discriminative dual chemosensors for picric acid (PA) and the arsenite (AsO33−) ion in aqueous medium. The sensing pathways were investigated by spectral titrations, time decay and DFT (B3LYP/def2–SVP) studies. The lowest detection limit has been discovered for the La analogue towards the sensing of both PA and AsO33− {or As(III)} ions with ∼0.22 and ∼1.46 ppb, respectively. Such MOFs exhibiting bifunctional sensing behaviour for an explosive (PA) as well as toxic ion, As(III), in the aqueous phase are disclosed as the first lanthanide 3D polymers with the lowest detection limit known so far for the said analytes.

Time-dependent seafloor roughness simulations using a coupled spectral ripple-biological decay model

Ever changing hydrodynamic conditions in the nearshore continuously affect biological communities and sediment features on the seafloor. Seafloor sediments have complicated interactions with the co-existing biological flora and fauna on the seabed. For example, ripple formation by waves and ripple degradation from biological activity are opposing forces occurring continuously. Simulating this complex natural environment is challenging due to these dynamic interactions of processes that span across a wide range of length and time scales. Existing seafloor models are often based on equilibrium conditions and neglect any change due to biological effects. Additionally, typical equilibrium ripple models provide only geometric dimensions, not a roughness spectrum necessary for acoustic applications. We present a time-varying spectral seafloor model, NSEA, that predicts the spatial and temporal evolution of seafloor roughness accounting for both the evolution and degradation of ripples due to hydrodynamics and biology. Model predictions are compared to high-frequency sector-scanning sonar data collected off the coast of Panama City, FL, during the Target and Reverberation Experiment (TREX13) and at the US Army Corps of Engineers Field Research Facility in Duck, NC. The sector-scanning sonar imaged ~15 square meters of the seafloor every 12 min for up to four weeks in depths up to 20 m.

Development of a direct time integration method based on Bezier curve and 5th-order Bernstein basis function

In this study, a robust unconditionally stable method for linear analysis of structures based on Bezier curves and Bernstein polynomials is proposed. The Bezier curve is used as interpolation function and Bernstein basis functions are applied for interpolation. The spectral radius, period elongation and amplitude decay are investigated for stability analysis, numerical dispersion and dissipation of proposed method, and results are compared with other methods that are the best in these properties. It is also shown that the behavior of the proposed method in analysis of finite element system is effective and reliable. To show the robustness and features of proposed method, a challenging problem with a very stiff and flexible response, a Howe truss under impact load, a frame under harmonic loading and a rectangular domain in plane strain condition are considered, and derived results are compared with references solutions and other results reported in the literature.

Two emission turn-on optical chemosensors for cysteine detection using up-conversion nanocrystals as excitation host: Synthesis, characterization and performance

In this paper, two rhodamine derived chemosensors were synthesized for cysteine optical recognition. Up-conversion NaYF4:Yb3+/Er3+ nanocrystals were modified as hydrophilic ones by α-cyclodextrin (α-CD) and used as excitation host, hoping to improve photostability of our chemosensors. Spectral analysis and emission decay lifetime comparison suggested that there was an efficient energy transfer between our excitation host and chemosensors. Job’s plot analysis indicated a simple recognition mechanism with binding stoichiometry of 1:1. Chemosensor emission was increased with increasing cysteine concentration, showing good selectivity and linear sensing response. The correlation between sensing performance and chemosensor molecular structure was discussed. Sulfur substituent effect improved selectivity of chemosensors.