Decay Curves Research Articles

Warm white light phosphors Sc2W3O12: Dy3+, Eu3+ with ultrahigh thermal stability and tunable luminescence

Phosphors for lighting applications often face challenges such as limited thermal stability, restricted tunability of emission colors, and moderate quantum efficiency. In this study, a series of Sc2W3O12: xDy3+, yEu3+ phosphors were synthesized via a high-temperature solid-state method to address these issues. Under 350 nm excitation, Sc2W3O12: xDy3+ phosphor exhibits blue (485 nm) and yellow emission peaks (577 nm), and the optimal doping concentration of Dy3+ is 3 mol%. In Sc2W3O12: 0.03Dy3+, yEu3+ phosphor, energy transfer is revealed through spectral overlap and fluorescence decay curve analysis of Dy3+ and Eu3+. The energy transfer efficiency is as high as 75 %, and the reason is explained through a combination of energy transfer mechanism and J-O theoretical calculation. By adjusting the range of y in Sc2W3O12: 0.03Dy3+, yEu3+, the correlated color temperature can be adjusted within the range of 4450 K to 3945 K, thereby achieving tunable luminescence from neutral white light to warm white light. The thermal stability of the synthesized warm white phosphor Sc2W3O12: 0.03Dy3+, 0.05Eu3+ is 90.38 % (423 K). The fluorescence intensity ratio of Eu3+ and Dy3+ at 303 K − 483 K was calculated, and its temperature sensing performance was analyzed. At 303 K, the thermal sensing factors are Samax = 0.97 % K−1 and Srmax = 0.0962 % K−1, and the actual quantum efficiency is IQE = 50.67 %. Finally, a WLED device was prepared using Sc2W3O12: 0.03Dy3+, 0.05Eu3+ phosphors. The device emits warm white light with a correlated color temperature of 3686 K. In summary, the prepared Sc2W3O12: Dy3+, Eu3+ phosphor successfully solved the challenges of limited thermal stability, tunable luminescence color and moderate quantum efficiency, and it has potential value in white light-emitting diodes (WLEDs) and optical thermometers.

Yb3+-Doped Titanate–Germanate Glasses for Near-IR Luminescence Applications: Synthesis, Characterization, and the Influence of TiO2 Concentration

In the framework of luminescent rare-earth-doped glasses for near-infrared applications, TiO2-containing inorganic glasses have been recently demonstrated to be a promising alternative to commercially used high-phonon SiO2-based glasses. This study investigates the effect of TiO2 concentration on the near-infrared spectroscopic properties of Yb3+ ions in multicomponent titanate–germanate glasses. A series of glass samples in the xTiO2-(60−x)GeO2-BaO-Ga2O3-Yb2O3 system (x ranging from 0 to 50 mol%) were synthesized using the melt-quenching technique. X-ray diffraction analysis confirmed the fully amorphous nature of the fabricated titanate–germanate samples. Fundamental spectroscopic properties of Yb3+-doped titanate–germanate system consisting of absorption spectra, near-IR emission spectra, and luminescence decay curves have been determined based on measurement using optical spectroscopy. The intensity of the emission band at 1 µm due to the 2F5/2 → 2F7/2 laser transition of Yb3+ ions increases by over 2.3-fold (TiO2 as the network former) compared to a barium gallo-germanate sample without TiO2. Our previous studies indicate that Yb3+-doped titanate–germanate glass is a promising optical material and could be successfully applied to laser technology.

Synthesis and luminescence properties of Ca2AlNbO6:Fe3+ phosphor for plant growth lighting

With the development of plant growth lighting, more and more attention has been paid to red and far red luminescent materials. In this work, we synthesize successfully a non-rare earth and non-toxic Ca2AlNbO6:Fe3+ phosphor in air and investigate the crystal structure, morphology, and luminescence properties of Ca2AlNbO6:Fe3+ by using powder X-Ray Diffraction, the field emission scanning electron microscopy, and the Edinburgh steady-state FS5 spectrometer, respectively. The far-red emission with peak at 714 nm of Ca2AlNbO6:Fe3+ is due to the 4T1(4G) → 6A1(6S) transition of Fe3+ ion. Photoluminescence excitation (PLE) spectrum of Ca2AlNbO6:Fe3+ includes four PLE peaks, which are assigned to the O2− → Fe3+ charge transfer band (CTB) (309 nm), the 6A1(6S) → 4T1(4P) (364 nm), 6A1(6S) → 4E(4D) (395 nm), and 6A1(6S) → 4T2(4G) (532 nm) transitions of Fe3+, respectively. We further study the concentration/temperature dependent emission spectra and time-resolved emission spectra. The optimal Fe3+ doping concentration (0.6mol%) and the only luminous center (Fe3+) in Ca2AlNbO6:Fe3+ are confirmed. The decay curves of Ca2AlNbO6:xFe3+ (0.2 mol% ≤ x ≤ 1.2 mol%) are measured and their lifetimes decrease from 463.24 to 385.29 μs＀ The emission spectra under different temperatures prove that Ca2AlNbO6:Fe3+ has a good heat stability. We explain the luminous mechanism and concentration/thermal quenching mechanisms, and further research the application prospect of Ca2AlNbO6:Fe3+ in plant growth lighting.

Luminescência opticamente estimulada em pastilhas de quartzo utilizando iluminação azul e verde

In this study, pellets fabricated from powdered rose quartz are investigated for their potential as ionizing radiation detectors, taking advantage of the abundant availability of quartz in the Earth's crust. For this purpose, optically stimulated luminescence (OSL) technique, using blue and green light stimulation, was used. The pellets were irradiated with a 90Sr/90Y beta source to doses from 80 to 550 mGy (dose rate = 0.08Gy/s). Analysis of the OSL decay curves showed a good fit with 3 exponential components (fast, medium, and slow). A linear dose-response relationship was observed within this interval of dose for both light stimulations. The repeatability of the OSL signal was found to be 3% for blue light and 2% for green light. Additionally, the fading experiment indicated that, after 1 hour, 41% and 35% of the OSL signal remains for blue and green stimulation, respectively. The results obtained highlight the promising usefulness of rose quartz-based pellets as effective detectors of ionizing radiation.

What determines travel time and distance decay in spatial interaction and accessibility?

The concept of ‘distance decay’ curves is used in spatial interaction and accessibility analysis to represent the diminishing likelihood of visiting places with increasing travel impedance, mainly distance and travel time. The shape of the resulting impedance decay curves varies by several factors, but these influential factors are often dismissed in favor of just travel mode. In this study, we examine which factors should be used to distinguish impedance functions for use. Using data from a large national travel survey, we first show that the impedance curves are well approximated by functions of the exponential family and the related Tanner function. We use two methods – variable-wise function fit and Shapley additive explanations – to conclude the importance of four factors for developing impedance functions. These are travel mode, trip purpose, urbanity class of trip origin and destination, and the socioeconomic status grouping of the travelers. We then show that the use of a generalized impedance function can significantly over- or underestimate spatial accessibility compared to factor-specific impedance function, with up to 80 % overestimation on average in the case of public transit and 16 % overestimation for low socio-economic status travelers. These findings highlight the importance of the choice of impedance function which has applications in spatial economics, transportation planning, and human mobility analyses.

Spectroscopic study and visible luminescence of Tb3+ ions in CaF2 crystal co-activated with Yb3+

High quality crystals with composition of Ca0.95Tb0.05F2.05 and Ca0.85Tb0.05Yb0.1F2.15 were grown by Bridgman-Stockbarger technique. Yb3+ ions were used as a sensitizer for Tb3+ ions. Optical properties were measured, including the absorption spectrum, emission spectrum, and fluorescence decay curves. Judd-Ofelt theory was used to analyze the spectroscopic parameters. Fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency were determined. The emission cross section of Tb3+ ions in Tb:CaF2 and Tb/Yb:CaF2 crystals for the green emission at 544 nm, corresponding to the transitions of 5D4→7F5 were calculated to be 4.61x10-22 cm2 and 4.60x10-22 cm2, respectively. Our experiments have shown that doping with Yb3+ ions does not significantly affect the spectral properties of Tb3+ ions in CaF2 crystal. Quadratic dependence of the emission intensity of Tb3+ ion in Tb/Yb:CaF2 crystal on the intensity of a diode laser at 955 nm proved that the excitation of Tb3+ ion occurs due to the cooperative process of transferring the excitation from two Yb3+ ions to one neighboring Tb3+ ion. The Tb/Yb:CaF2 crystal can be considered as a promising up-converting medium for creating diode-pumped visible phosphorus and active laser media.

Multifunctional Near-Infrared Luminescence Performance of Nd3+ Doped SrSnO3 Phosphor

The phosphors with persistent luminescence in the NIR (near-infrared) region and the NIR-to-NIR Stokes luminescence properties have received considerable attention owing to their inclusive application prospects in the in vivo imaging field. In this paper, Nd3+ doped SrSnO3 phosphors with remarkable NIR emission performance were prepared using a high temperature solid state reaction method; the phase structure, morphology, and luminescence properties were discussed systematically. The SrSnO3 host exhibits broadband NIR emission (800–1300 nm) with absorptions in the near ultraviolet region. Nd3+ ions emerge excellent NIR-to-NIR Stokes luminescence under 808 nm laser excitation, with maximum emission at around ~1068 nm. The concentration-dependent luminescence properties, temperature dependent emission, and the luminescence decay curves of Nd3+ in the SrSnO3 host were also studied. The Nd3+ doped SrSnO3 phosphors exhibit exceptional thermal stability; the integrated emission intensity can retain approximately 66% at 423 K compared to room temperature. Most importantly, NIR persistent luminescence also can be observed for the SrSnO3:Nd3+ samples, which is in the first and second biological windows. A possible mechanism was proposed for the persistent NIR luminescence of Nd3+ based on the thermo-luminescence spectra. Consequently, the exciting results indicate that multifunctional NIR luminescence has been successfully realized in the SrSnO3:Nd3+ phosphors.

Multifunctional thermally activated delayed fluorescence emitter for both doped and non-doped organic light emitting diodes

Developing efficient smart materials that display mechanochromic luminescence (MCL) and thermally activated delayed fluorescence (TADF) remains a formidable challenge. Herein, we designed and synthesized a multifunctional emitter, 2BPy-mTC, where benzoyl pyridyl (2BPy) acts as an acceptor and 3,6-di-tert-butyl-9H-carbazole (TC) acts as a donor. 2BPy-mTC exhibits blue emission with λmax of 456 nm in pristine form and emission shifted to green with λmax of 495 nm upon grinding. Interestingly, when fumed with CH2Cl2, the emission reverts to deep blue at λmax of 440 nm. 2BPy-mTC possesses a ΔEST of 0.20 eV in neat film and 0.11 eV in doped film (5 wt% 2BPy-mTC: mCBP) and exhibits a PLQY of 42 % in neat film and 59 % in doped film. The transient photoluminescence (PL) decay curves show a delayed lifetime of 110.3 μs for the neat film and 192.9 μs for the doped film and confirm the TADF property in both doped and non-doped film. It shows an EQEmax of 16.3 % in doped device with an emission maximum of 484 nm. Conversely, it retains the EQEmax of 13.8 % in non-doped device with a slight red shift in the emission maximum (496 nm). This discovery opens a new avenue for designing multifunctional emitters with improved EL performance.

Laser Characteristics of Er3+/Yb3+:K-BaF2-Al-Phosphate Glasses.

Er3+ and Er3+/Yb3+-doped phosphate-based glasses have been synthesized by melt quenching technique and are characterized by absorption spectra, infrared emission, decay curves, Fourier transform infrared spectrum and up-conversion studies. From the absorption spectra, intensity parameters and radiative properties have been derived utilizing the Judd-Ofelt theory. Er3+-doped glass is found to have larger radiative lifetime for the laser originating from 4I13/2 level at 1537 nm. Infrared and visible characteristic emissions have been measured by exciting at 790 nm through down- and up-conversion, respectively. The up-conversion spectra consist of intense green emission at around 525 and 545 nm ascribed to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, respectively, and a weak red emission at around 656 nm due to the 4F9/2 → 4I15/2 transition of Er3+ ions. Various spectroscopic and laser characteristics of these glasses have been calculated and compared with those of similar reported ones.

A Cr3+-triggered near-infrared tungstate phosphor for organic compound non-destructive detection

Cr3+-doped near-infrared (NIR) luminescent materials have become a research hotspot in luminescence functional materials. However, developing NIR phosphors with emission wavelengths exceeding 1000 nm, suitable for organic compound non-destructive analysis, remains a significant challenge. In this study, LiSc(WO4)2:Cr3+ NIR phosphors were synthesized using a simple solid-state reaction method. Low temperature photoluminescence emission spectrum, electron paramagnetic resonance spectrum, and fluorescence decay curve confirmed that Cr3+ ions occupied both LiO6 and ScO6 octahedron sites, forming two luminescence centers. The sample exhibited an emission wavelength of 1082 nm under 523 nm excitation, with a full width at half maximum (FWHM) of 290 nm. As the Cr3+ concentration increased, the emission peak showed a blue shift. The sample LiSc(WO4)2:0.3Cr3+ with optimal optical performance exhibited an emission wavelength of 1023 nm and an FWHM of 228 nm. Its luminescence intensity retained 38.4% of room temperature value at 380 K, and the internal and external quantum efficiency were 33.2% and 18.9%, respectively. When packaged with a 525 nm green LED, the device as a NIR light source is capable of accurately identifying water, ethanol, ammonia, and silicone oil. This work demonstrates that tungstate materials have great potential in the field of optical materials and offers a new perspective for selecting matrix materials in the development of Cr3+-doped long-wavelength broadband NIR phosphors.

Isothermal Decay Analysis of Thermoluminescence Peaks of Nano-α-Alumina

This study investigates the thermoluminescence (TL) behavior of nano α-Al2O3 (40 nm) within the temperature range of 110 to 160°C to elucidate the kinetic mechanisms governing its TL response. The isothermal decay curves were analyzed to determine the order of kinetics and activation energies of the TL peaks. The ln(I) vs. time plot revealed a nonlinearity starting at 140°C, indicating that the TL peaks do not follow first-order kinetics in this temperature region. Subsequent analysis confirmed that the TL data align with second-order kinetics, with a kinetic-order parameter of b = 2.0 providing the best linear fit. Further examination of the ln(slope) vs. 1/kT relationship revealed a composite structure in the TL response, characterized by three distinct linear sections. These sections correspond to activation energies of 0.6±0.12 eV, 1.07±0.25 eV, and 1.61±0.47 eV, respectively, suggesting the presence of three different centers contributing to the dosimetric peak. The findings underscore the complex nature of the TL response in nano α-Al2O3, highlighting the necessity of considering multiple kinetic components in the analysis of its TL properties. This study enhances our understanding of the thermoluminescent behavior of nano α-Al2O3 and provides a basis for further research into its applications in dosimetry

Novel reddish-orange emitting BaBPO5:Eu3+ phosphor for n-UV warm white-LEDs: Synthesis and study of structural and spectroscopic investigations

A novel reddish-orange emitting 2Ba2-xO-B2O3-P2O5:xEu3+ (x= 0.04, 0.06, 0.08, 0.10, 0.12 and 0.14 mol%) phosphor with different concentrations of Eu3+ ions were synthesized through high temperature solid-state reaction technique. The crystal structure has been studied by X-ray diffraction technique for all the concentrations of Eu3+ ions. The morphology and elemental analysis of the optimal ∼0.1 mol% concentration was examined by the SEM-EDS images. The functional groups were analysed by the FTIR characterization technique. The thermal properties were studied by the TGA-DSC analysis. The energy band gap of all the samples were analysed by using UV–VIS DRS technique. The photoluminescence properties of BaBPO5:Eu3+ phosphor with different concentrations of Eu3+ ions were investigated at λem = 611 nm and λex = 394 nm. Variation in emission intensity with Eu3+ ion concentrations, phonon side bands, multi-phonon relaxation rate and energy transfer mechanisms were studied. The BaBPO5:Eu3+ phosphors exhibit characteristic emission peaks corresponding to 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ ions under n-UV excitation. Among all the transitions, 5D0 → 7F1 (593 nm) transition shows higher intensity and asymmetric ratio (R21) for all concentrations of Eu3+ ions were calculated. The lifetimes of 5D0 level of Eu3+ ions in BaBPO5: Eu3+ phosphor were calculated by using fluorescent decay curve analysis. The CIE color coordinates reveal, reddish-orange emission in the low CCT range. These findings imply that BaBPO5: 0.1Eu3+ phosphor is a promising candidate for solid-state lighting applications as well as phosphor-converted warm w-LEDs.

Structure-Photoluminescence Relationship in Ce3+-Doped K5Y(P2O7)2 and Its Sensitization to Dy3+ with Enhanced White Light Emission.

From a fundamental point of view, the structure-photoluminescence relationship is vitally important for developing efficient phosphors and rationally improving their performances. In this work, Rietveld refinements on high-resolution powder X-ray diffraction (XRD) data were conducted to verify the Ce3+ distribution in K5Y(P2O7)2 (KYPO). Ce3+ ions are located at both M1 and M2 sites, with occupation factors of 0.31(2) and 0.19(2), respectively. Importantly, the crystal field strength (CFS) is stronger at the former site due to the larger bond valence sum. Correspondingly, the Ce3+ emission can be deconvoluted into four Gaussian-type bands centered at ∼353, ∼383, ∼343, and ∼369 nm, where the former two belong to Ce3+ at the M1 site and the latter two are assigned to Ce3+ at the M2 site. Ce3+ in KYPO is a highly efficient activator, with optimal internal and external quantum efficiencies of 98.9 and 74.6%, respectively, and was thus utilized to sensitize the Dy3+ emission. Indeed, energy transfer from Ce3+ to Dy3+ was confirmed by fluorescent decay curves for Ce3+/Dy3+ codoped KYPO, and the mechanism was supposed to be dominated by dipole-dipole interactions. Indeed, it can be pumped by a 310 nm LED chip and emits a bright white light. Ce3+ photoluminescence exhibits high resistance to thermal quenching, and it can be further enhanced by codoping Dy3+, i.e. the emission intensity remains 96.3% at 423 K.

Gan Photonic Crystals: Spectral Dynamics in UV, X‐Ray, and Alpha Radiation

In this work, a comparative analysis of gallium nitride (GaN) thin films is conducted, both with and without photonic crystal (PhC) structures, focusing on their scintillation and photoluminescence properties. GaN's suitability for diverse optoelectronic and radiation detection applications is analyzed, and this study examines how PhC implementation can enhance these properties. Methodologically, the emission spectra is analyzed from 5.9 keV X‐ray sources, decay curves, pulse height spectra in response to 241Am 5.5 MeV alpha‐rays, and photoluminescence spectra induced by UV excitation. The findings demonstrate a substantial increase in quantum efficiency for PhC GaN, nearly tripling the light yield that of conventional plain GaN thin films under the UV excitation. The enhancement is predominantly attributed to the PhC GaN's proficiency in guiding light at 550 nm, a feature indicative of its spectral filtering capabilities, as detailed in the study. Furthermore, side‐band scintillations, stemming from inherent materials like Chromium that generate scintillations at diverse wavelengths, are effectively mitigated. A key finding of this study is the effective detection of light not only at the rear but also along the lateral sides of the films, offering new possibilities for radiation detector design and architecture.

Er3+ -doped oxyfluoroborosilicate glass ceramics with embedded CaF2 nanoparticles for 1.53 μm broad band applications

The CaF2 based oxyfluoroborosilicate glasses and glass ceramics doped with Er3+ ions were prepared via melt quench process followed by heat treatment and characterized for 1.53 μm broadband applications. The optimized glass ceramic sample was obtained at 450oC/1h heat treatment. The Er3+ concentration was optimized as 1.0 mol% for efficient emission at 460 nm excitation through concentration dependent luminescence analysis. The spectroscopic parameters such as Ωλ = 2,4,6 parameters and the radiative parameters such as spontaneous transition probability rates (AR), branching ratios (βR) and decay times (τR) were calculated applying the standard Judd-Ofelt theory. The effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff), quantum efficiency (η) and figure of merit (σe × τR) were calculated as 25.78 nm, 13.42 × 10−21 cm2, 3.46 × 10−26 cm3, 82.83% and 5.32 × 10−23 cm2s, respectively for the optimized glass ceramic sample. The exchange type of energy transfer among the excited Er3+ ions results the quenching in luminescence and the non-exponentiality in decay curves. The systematic investigations carried out indicate that the glass ceramic obtained at 450oC/1h heat treatment was proficient for 1.53 μm broadband fiber lasers and optical amplifiers in S and C band communication window.

Metabolite T2 relaxation times decrease across the adult lifespan in a large multi-site cohort.

Relaxation correction is crucial for accurately estimating metabolite concentrations measured using in vivo MRS. However, the majority of MRS quantification routines assume that relaxation values remain constant across the lifespan, despite prior evidence of T2 changes with aging for multiple of the major metabolites. Here, we comprehensively investigate correlations between T2 and age in a large, multi-site cohort. We recruited approximately 10 male and 10 female participants from each decade of life: 18-29, 30-39, 40-49, 50-59, and 60+ y old (n = 101 total). We collected PRESS data at eight TEs (30, 50, 74, 101, 135, 179, 241, and 350 ms) from voxels placed in white-matter-rich centrum semiovale (CSO) and gray-matter-rich posterior cingulate cortex (PCC). We quantified metabolite amplitudes using Osprey and fit exponential decay curves to estimate T2. Older age was correlated with shorter T2 for tNAA2.0, tCr3.0, tCr3.9, tCho, and tissue water (CSO and PCC), as well as mI and Glx (PCC only); rs = -0.22 to -0.63, all p < 0.05, false discovery rate (FDR)-corrected. These associations largely remained statistically significant when controlling for cortical atrophy. By region, T2 values were longer in the CSO for tNAA2.0, tCr3.9, Glx, and tissue water and longer in the PCC for tCho and mI. T2 did not differ by region for tCr3.0. These findings underscore the importance of considering metabolite T2 differences with aging in MRS quantification. We suggest that future 3T work utilize the equations presented here to estimate age-specific T2 values instead of relying on uniform default values.

Insights into the Structural, Thermal/Dilatometric, and Optical Properties of Dy3+-Doped Phosphate Glasses for Lighting Applications.

Dysprosium-doped glasses are of interest for applications in light-emitting devices, yet the full range of effects of Dy3+ ions on glass properties is not fully understood. In this work, phosphate glasses with 50P2O5-(50 - x)BaO-xDy2O3 (0 ≤ x ≤ 4.0 mol %) nominal compositions were prepared by melting and the impact of Dy3+ ions on glass physical, structural, thermo-mechanical, and optical properties was evaluated. Following refractive index, density, and X-ray diffraction characterizations, the glasses were studied comprehensively through Raman spectroscopy, X-ray photoelectron spectroscopy, dilatometry, optical absorption, and photoluminescence (PL) spectroscopy. The thorough investigation and data analyses shed light on the Dy3+-driven structural and thermal properties reported here for the first time. The thermal expansion behavior was put in context with the reported data for other lanthanides and analyzed in the framework of the high ionic field strengths, leading to tighter glass networks. Further, a detailed analysis of the absorption, PL, and emission decay curves was carried out, providing insights into the origin of the optical behavior. Supported is the hypothesis that the cross-relaxation channels between Dy3+ ions taking place at low concentrations are responsible for the decrease in the decay times while the PL attractive for lighting applications still improves. Conversely, high Dy3+ concentrations facilitate the emission quenching proceeding via an electric dipole-dipole interaction likely incorporating the resonant excitation migration pathway for Dy3+-Dy3+ mean distances shorter than ∼15 Å.

The non-exponential decay characteristics of HTS NI-class coils in sudden discharge experiments

Abstract The decay of the voltage and magnetic field of the high-temperature superconductivity (HTS) no-insulation-class (NI-class) coil in the sudden discharge experiment is usually considered to be exponential. However, our experiment found that it is not accurate to describe the decay characteristics of the NI-class coil with a simple exponential function. Combined with equivalent circuit models of the NI-class coil, we use the theory of ordinary differential equations to explain the non-exponential decay characteristics and point out that it is closer to the matrix exponential characteristics. Based on this finding, we believe that the non-uniform turn-to-turn contact resistivity (TTCR) is an important cause of the non-exponential decay characteristics of the NI-class coil. Reverse thinking leads us to realize that the voltage decay curve of the NI-class coil in the sudden discharge experiment contains the distribution information of its TTCR. Therefore, we propose a method for measuring the TTCR of NI-class coils based on the matrix exponential model. The co-simulation combining the finite element model and the equivalent circuit model shows that the non-uniformly distributed TTCR has a great influence on the transient process of the NI-class coil, which makes the current and current density in the transient process vary greatly in different regions of the NI-class coil. Those findings mean that the simulation study of the NI-class coils and magnets with uniform TTCR usually used in the past may be far from the actual situation.

Novel Approach for Lifetime-Proportional Luminescence Imaging Using Frame Straddling.

Optode-based chemical imaging is a rapidly evolving field that has substantially enhanced our understanding of the role of microenvironments and chemical gradients in biogeochemistry, microbial ecology, and biomedical sciences. Progress in sensor chemistry has resulted in a broadened spectrum of analytes, alongside enhancements in sensor performance (e.g., sensitivity, brightness, and photostability). However, existing imaging techniques are often costly, challenging to implement, and limited in their recording speed. Here we use the "frame-straddling" technique, originally developed for particle image velocimetry for imaging the O2-dependent, integrated luminescence decay of optical O2 sensor materials. The method synchronizes short excitation pulses and camera exposures to capture two frames at varying brightness, where the first excitation pulse occurs at the end of the exposure of the first frame and the second excitation pulse at the beginning of the second frame. Here the first frame truncates the luminescence decay, whereas the second frame fully captures it. The difference between the frames quantifies the integral of the luminescence decay curve, which is proportional to the luminescence lifetime, at time scales below one millisecond. Short excitation pulses avoid depopulation of the ground state of luminophores, resulting in a linear Stern-Volmer response with increasing concentrations of the quencher (O2), which can be predicted through a simple model. This methodology is compatible with a wide range of camera systems, making it a versatile tool for various optode based chemical imaging applications. We showcase the utility of frame straddling in measuring O2 dynamics around algae and by observing O2 scavenging sodium dithionite particles sinking through oxygenated water.

Combustion synthesis and photoluminescence of Ca2SrWO6:Dy3+ double perovskite: An approach for white light emission

Luminescent Ca2SrWO6:Dy3+ double perovskites are synthesized via the combustion route of material synthesis, wherein urea is taken as fuel. The as-prepared phosphor series comprehensively characterized for their structural and photoluminescence (PL) properties. The Rietveld refinement of XRD data revealed monoclinic crystallized microcrystals with mixed particles of the size of less than 1 µm, studied via SEM. Ca2SrWO6:Dy3+ displayed standard Dy3+ transitions 4F9/2–6H15/2 (blue emission) and 4F9/2–6H13/2 (yellow emission) collectively resulted in white light emission, confirmed via CIE study. Under 278 and 388 excitations, 2 mol% doping of Dy3+ found to be optimum concentration, beyond which concentration quenching is observed due to dipole–dipole interaction. The Y/B ratio ∼1 shows potential to produce white light and make phosphor suitable for WLED applications. The Ca2SrWO6:Dy3+ phosphor displayed notably high thermal stability with PL intensity persisted 77.6 % at LED burning temperature (150 °C) when compared to PL intensity attained at room-temperature, which is basically due to the rigid perovskite structure. In addition, the PL decay lifetime of 4F9/2 state was calculated by utilizing decay curves. Subsequently, the PL quantum efficiency and non-radiative relaxation rate are determined. The theoretical model of Auzel’s fit function is used to calculate to quantum efficiency and was found to be 93.27 % for Ca2SrWO6:2 % Dy3+ phosphor. Moreover, the photometric results reveals that the CIE points are lies in white region of CIE diagram with comparable CCT. The collective results indicated the utility of the phosphor for potential WLED applications.