Decay Time Values Research Articles

Temporally Resolved Type III Solar Radio Bursts in the Frequency Range 3–13 MHz

Radio observations from space allow to characterize solar radio bursts below the ionospheric cutoff, which are otherwise inaccessible, but suffer from low, insufficient temporal resolution. In this Letter we present novel, high-temporal resolution observations of type III solar radio bursts in the range 3–13 MHz. A dedicated configuration of the Radio and Plasma Waves (RPW) High Frequency Receiver (HFR) on the Solar Orbiter mission, allowing for a temporal resolution as high as ∼0.07 s (up to 2 orders of magnitude better than any other spacecraft measurements), provides for the very first time resolved measurements of the typical decay time values in this frequency range. The comparison of data with different time resolutions and acquired at different radial distances indicates that discrepancies with decay time values provided in previous studies are only due to the insufficient time resolution not allowing to accurately characterize decay times in this frequency range. The statistical analysis on a large sample of ∼500 type III radio bursts shows a power low decay time trend with a spectral index of −0.75 ± 0.03 when the median values for each frequency are considered. When these results are combined with previous observations, referring to frequencies outside the considered range, a spectral index of −1.00 ± 0.01 is found in the range ∼0.05–300 MHz, compatible with the presence of radio-wave scattering between 1 and 100 R ☉.

Tip‐Enhanced Imaging and Control of Infrared Strong Light‐Matter Interaction

AbstractOptical antenna resonators enable control of light‐matter interactions on the nano‐scale via electron–photon hybrid states in strong coupling. Specifically, mid‐infrared (MIR) nano‐antennas coupled to saturable intersubband transitions in multi‐quantum‐well (MQW) semiconductor heterostructures allow for the coupling strength to be tuned through antenna resonance and field intensity. Here, tip‐enhanced nano‐scale variation of antenna‐MQW coupling across the antenna is demonstrated, with a spatially‐dependent coupling strength varying from 73 (strong coupling) to 24 (weak coupling). This behavior is modeled based on the spatially dependent local constructive and destructive interference between tip and antenna fields. Using a quantum‐mechanical density‐matrix model of the MQW system with its designed values of transition dipole moment, doping density, and population decay time, the picosecond IR pulse coupling to intersubband transitions and the associated tip induced strong‐field saturation effects are described. These results present a new regime of nonlinear IR light‐matter control based on the dynamic manipulation of quantum hybrid states on the nanoscale and in the infrared, with a perspective regarding extension to molecular vibrations.

Pressure modified upconversion luminescence of Yb3+ and Er3+-doped Bi3TeBO9 ceramics

Yb3+ and Er3+-doped Bi3TeBO9 ceramics exhibit efficient upconversion luminescence in the visible spectral range upon laser diode excitation at 975 nm. Bi3TeBO9:Yb3+/Er3+ powder was prepared by means of the modified Pechini method. A series of Bi3TeBO9:Yb3+/Er3+ ceramic samples was fabricated using the high-pressure low-temperature technique, by sintering Bi3TeBO9:Yb3+/Er3+ powder under different pressures (2, 4, 6 or 8 GPa). The structure and morphology of the above-mentioned samples were analyzed using XRD, SEM and EDX measurements. The phonon energy of Bi3TeBO9 matrix associated with the vibrations of TeO6 and BO3 molecular groups was revealed using μ-Raman spectroscopy. The low phonon energy of Bi3TeBO9 matrix allows the effective energy transfer between Yb3+ and Er3+ ions as well as the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions from the excited to ground states of Er3+ ions, resulting in efficient upconversion emission at 523, 540 and 653 nm, respectively. The decay times determined for all analyzed emissions were longer for Bi3TeBO9:Yb3+/Er3+ ceramics than for the powder sample. The highest values of decay times were detected for the ceramics obtained under a pressure of 8 GPa and were equal to 174, 172 and 175 μs for the emissions at 523, 540 and 653 nm, respectively. The obtained results suggest that Bi3TeBO9:Yb3+/Er3+ ceramics can be proposed as efficient spectral converters in the new type solar cells enhancing the efficiency of the photovoltaic effect.

Sensitizing effect of Yb3+ ions on 1.53 µm broadband and 548nm upconversion green emissions of Er3+-doped TeO2–WO3–GeO2 glasses

The Er3+-doped transparent glasses were the significant materials to design solid state visible lasers, near infrared lasers, upconverters, sensors and fiber amplifiers. The effect of Yb3+ sensitization on 1.53 µm broadband and 548 nm upconversion green emissions in TeO2–WO3–GeO2–ErF3–YbF3 (TWGErYb) glasses were studied. They were characterized through structural, optical absorption, near infrared and upconversion studies. The Judd-Ofelt theory was adopted to estimate several spectroscopic and radiative parameters. The laser characteristic parameters such as stimulated emission cross sections, gain band widths, figure of merit and quantum efficiencies were evaluated. Conveying the energy from Yb3+ to Er3+ ions and the reasons for non-radiative losses were highlighted. The quenching in luminescence of 1.53 µm broadband, the 548 nm upconversion green emissions and the enhanced decay time values due to self-absorption were studied. The fitting of decay curves of Er3+: 4I13/2 and Er3+: 4S3/2 emission states at higher Yb3+concentrations (≥1.5 mol%) to Inokuti-Hirayama model were discussed. The TWGErYbx glasses containing 0.5Er3+/2.5Yb3+ show proficiency to design 548 nm green solid state lasers and 1.53 µm broadband fiber lasers.

Effect of Gadolinium Oxide and Gadolinium Fluoride in Borophosphate Glasses Doped with Tb2O3 Content

The melt-quenching process synthesized gadolinium oxide and fluoride in borophosphate glasses doped with terbium ions (Tb3+). The effect of fluoride compounds and their impacts on physical, optical, and luminescent properties have been investigated. The glasses absorbed near-infrared, visible light, and ultraviolet photons. The bright green emission circa 542 nm via the 5D4 → 7F5 radiative state of Tb3+ originated. Depending on the excitation, there are several sorts of ultraviolet, visible light, and X-ray. The values of decay time are in the order of milliseconds (ms). The Gd3+-Tb3+ energy transfer is vital in green emission under 275 nm excitation. According to the results obtained in this work, the developed glasses can be suitable candidates for green emission medium.

Luminescence properties and energy transfer of Nd3+- Er3+/ Nd3+-Pr3+ co-doped LFP glasses system

The motivation for this research is that the emission spectra using directly pumped laser diodes have not yet been found. We want to explore the luminescence properties of a co-doped laser material utilizing a diode laser as an optical pump. The research method used standard melt-quench and was stimulated by a laser diode (808 and 980 nm). The double doped of Nd3+- Er3+/Nd3+-Pr3+ ions with glasses system of lithium-fluorophosphate (LFP) had a strong band emission at 1056 nm, which transitioned at 4F3/2 → 4I11/2 and showed a drop in intensity from co-doping with Er3+ and Pr3+ ions. The fluorescence width at half maximum (FWHM) of the glasses is calculated to identify whether the sample may be used as a laser application. The FWHM values are found to be 22–28 nm. Decay time values were shown to decrease with increasing concentrations of Er3+ and Pr3+ ions and were used for energy transfer calculations. The Quantum Yields (QYs), efficiency in the transfer of energy and the possibility transfer energy were measured and calculated that confirm the possibility of energy transfer from Nd3+ to Er3+ and Pr3+ ions. Since, the emission spectrum at 1535 nm was found, this is a good reason for it to be used as an optical device.

Ultraviolet photodetectors based on ZnO nanowires with SiO2/ZnO multilayers

Ultraviolet photodetectors (UV PDs) have been a frequently studied focus of optoelectronic semiconductor devices because of their large range of applications. As one of the most famous materials in third-generation semiconductors, ZnO-based UV PDs have received a great deal of attention in various research areas. Due to the carrier transport channel and higher exciton bond energy, ZnO nanowires (NWs) have better photoelectron sensitivity under UV light than ZnO films. Here, well-organized ZnO NWs were fabricated on ZnO-seeded substrates via a hydrothermal method. Multilayers of double SiO2/ZnO(S/Z) layers were designed on the NWs, and the Schottky barrier was introduced by the close contact of the ZnO NWs and gold electrodes to improve the performance of ZnO UV PDs. Characteristics of the dark current, photocurrent, rise time, decay time, photo-to-current ratio (S), and responsivity values (Rs) of the PDs were studied. Furthermore, multilayer UV PDs were achieved on both Si and quartz substrates. S of the ZnO S/Z-based UV PDs fabricated on a silica substrate can reach 55.57, which is better than the values of ZnO UV PDs reported previously. Compared with silica-based UV PDs with S/Z layers, quartz-based UV PDs with S/Z layers show a higher performance of Rs, which reach 12.62 A/W. ZnO NWs with multilayers and the Schottky contact between ZnO NWs and Au are promising candidates in high-sensitivity UV PDs.

Spectroscopic studies of Pr3+ doped red-emitting BaO–ZnO– Li2O–P2O5 glasses for luminescent devices applications

Pr3+ doped BaO–ZnO– Li2O–P2O5 (BZLP) glass samples synthesised through melt quenching route were studied. The x-ray diffraction (XRD) confirms the amorphous non-crystalline nature of undoped and doped BZLP glass. Absorption spectra show several bands in ultraviolet, visible and infrared regions. The absorption data was used in Judd-Ofelt (J-O) theory to evaluate various radiative parameters. Three peaks are visible in the photoluminescence (PL) emission spectra with the strongest peak positioned at 604 nm for which stimulated emission cross section and quantum efficiency has been assessed. The CIE color coordinates of the samples lie in the red region. The decay time values for 604 nm emission decreased with increased Pr3+ concentration. The luminescence intensity decreased to 88.12% and 82.61% of maximum value at 423 K and 473 K respectively showing high thermal stability. These BZLP glasses can work as an effective deep red-emitting component for w-LEDs and other photonic applications.

Luminescence characteristics of Dy3+ doped sodium alumina borate glass: Role of silver

Metallic nanoparticle (NP) doped glasses have been studied as promising candidates for various technological applications due to their ability to improve the luminescence properties of rare earth ions. In this work, Dy2O3 and Ag2O co-doped sodium alumina borate glasses were synthesized by conventional melt-quenching technique. Raman analysis verified the existence of [BO3] and [BO4] groups with B–O stretching vibrations in the prepared glasses. Transmission electron microscope images confirmed the presence of spherical Ag NPs, whose average diameter is about 7.60 nm, in H-0.5Dy1Ag glass matrix. The optical and luminescence properties were investigated according to Ag concentrations. The negative value of the bonding parameters, calculated from the absorption spectra, indicates the ionic nature between the Dy3+ ions and its surrounding ligands. In order to determine the nature of the Dy-O bond and the symmetry around the Dy3+ ion environment, Judd–Ofelt intensity parameters (Ω λ, λ = 2, 4, 6) were obtained from the absorption spectra. The luminescence spectra obtained under 350 nm excitation exhibits four emission bands at 481 (4F9/2→6H15/2), 572 (4F9/2→6H13/2), 662 (4F9/2→6H11/2), and 750 (4F9/2→6H9/2) nm. The intensity of emission spectra increases with Ag2O content until 1.0 wt% in H-0.5Dy-yAg glasses and then decreases due to the back-energy transfer (ET) from Dy3+ to Ag+. The ET mechanism from Ag+ to Dy3+ ion for H-1Ag-xDy glasses were investigated through Forster-Dexter’s theory and were found to be quadrupole-quadrupole type. The various radiative properties were calculated by using Judd-Ofelt intensity parameters and emission spectra. It was found that the 572 nm emission band, located in the yellow region, has higher radiative parameters. As a function of Ag concentration, the Y/B values, Commission Internationale d’Eclairage (CIE) chromaticity coordinates (x,y) and correlated color temperatures (CCT) were evaluated. The CIE chromaticity coordinates and CCT values of all glasses are located in the white light region. The decay time values of 1S0→3D1 transition of Ag+ ions and 4F9/2→6H13/2 transition of Dy3+ ions confirm the ET from Ag+ to Dy3+ ions. Overall, the present study indicates that the synthesized glasses with Ag addition exhibits improved luminescence, making them potential candidate for white LEDs.

Optimized microwave assisted synthesis of La2(WO4)3:Tb3+ phosphors and analysis of photoluminescence behavior

NUV/blue LED excitable green emitting terbium doped lanthanum tungstate nanophosphors were successfully synthesized via optimized microwave assisted co–precipitation technique for the first time. Powder XRD analysis confirms that the nanophosphor have monoclinic structure and belongs to space group C2/c. FTIR spectrum identified the characteristic vibrational modes of tungstate group. The chemical composition of the sample was confirmed with the help of EDS technique. Thermogravimetric analysis (TGA) ascertained the outstanding thermal stability of the prepared sample. The strong and wide charge transfer band in the excitation spectrum clearly demonstrates the efficient energy transfer from the host matrix to the terbium ion. This broad band allows for NUV excitation, and the sharp peak at 487 nm indicates that blue LED sources can also be used for excitation. The presence of prominent peak at 543 nm in the emission spectrum, due to 5D4→7F5 transition irrespective of the excitation wavelength, uplifts terbium doped lanthanum tungstate to the group of excellent green emitting phosphors. Decay curves shows single exponential nature and fluorescence life time was obtained. The small value of decay time implies that the synthesized material is suitable for display applications. The calculated CIE chromaticity co–ordinates are close to green emitting phosphors. Thus, terbium doped lanthanum tungstate phosphors are potential phosphors with green emission for WLED applications.

White Emission from Dy3+ Doped in ZnO – CaO – B2O3 for WLEDs Material Application

The Dy3+ ions doped CaO-ZnO-B2O3 glasses were synthesis by the melt quenching technique with various Dy2O3 concentrations to investigation physical and optical properties. The results showed that the density and the molar volume trend to be increased along with increased Dy3+ concentration. The absorption spectra showed characteristic absorption peaks in the visible and near infrared regions. Judd–Ofelt (JO) intensity parameters have been obtained from the optical absorption spectra. The emission spectra of the glasses are illustrated the highest emission intensity at 574 nm wavelength, which corresponding to Dy3+ transition 4F9/2→6H13/2 level. The decay time value decreased as the concentration of Dy2O3 increased. The CIE 1931 chromaticity investigation showed that Dy3+ doped glasses emitted light with white color.

Radiative properties of ‘Eu’in Li–Al–Si–O ceramics: Effect of ‘Si’ to ‘Li’ ratio

Four Li–Al–Si– O -based ceramic compounds with varying Si to Li ratios were synthesized via a high-temperature reaction route and characterized by X-Ray diffraction, scanning electron microscopy, and photoluminescence techniques. Eu was used as an activator in these four compositions namely, LiAlSiO 4 , LiAlSi 2 O 6 , LiAlSi 3 O 8 , and LiAlSi 4 O 10 , and the radiative properties were evaluated. The activator concentration was optimized in all these samples to 2 mol%. The photoluminescence emission intensity and decay time values increased with the Si to Li ratio. The relative intensities of the emission spectra and the lifetime values indicated that the rare earth ion stabilizes itself at interstitial positions in the lattice having approximately C 2v symmetry. The chromaticity indices for the four ceramic samples doped with Eu were calculated that showed near red emission for all. To get an idea about their commercial utility, color purity, quantum efficiencies for the phosphors were evaluated. The emission profile of the prepared samples was compared with a commercial sample. The Judd-Ofelt parameters, transition probabilities, branching ratios, and quantum efficiencies were also calculated for these systems. It was observed that the metal-ligand bond covalency decreased with an increase in the Si to Li ratio which was responsible for the increase in the emission intensities and luminescence decay time values.

Sol-gel derived Li and Mg incorporated nickel oxide particles: An investigation on structural and optical properties

In this study, NiOx, Li:NiOx, and Li,Mg:NiOx powders (Li0.05MgaNi(0.95-a)Ox, a: 0.00; 0.05; 0.1; 0.15; 0.30) were produced by sol-gel method. Preformed powders were annealed at 350 °C, 500 °C, and 650 °C to monitor structural changes. Functional groups, compositions, phase structures, elemental analysis, morphology, and optical properties were investigated by Fourier transforms infrared spectroscopy (FTIR), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and photoluminescence measurements (PL), respectively. The incorporation of Li+ and Mg2+ into NiOx structure was successfully accomplished as seen on XPS results. Crystallite size decreased upon increasing dopant concentration. All of the powders, with bi-exponential decay curves, exhibited maximum emission peak at 550 nm under the excitation at 362 nm. A decrease in both emission based intensity and average decay time values was observed at addition of Li+ and Mg2+ into structure with respect to the pristine NiOx.

Development of Composite Scintillators Based on the LuAG: Pr Single Crystalline Films and LuAG:Sc Single Crystals

The scintillation properties of novel type of composite scintillator based on Lu3Al5O12:Pr (LuAG:Pr) single crystalline film (SCF) and LuAG:Sc substrate grown by the liquid-phase epitaxy method are considered in this work. The registration of α-particles and γ-quanta in such types of composites occurs by means of separation of the scintillation decay kinetics of SCF and crystal parts, respectively. Namely, under excitation by α-particles of 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source, the large differences in the respective scintillation decay kinetics and decay time values tα and tγ are observed for the LuAG:Pr SCF/LuAG:Sc SC composite scintillator with various film thicknesses. Furthermore, the best tγ/tα ratio above 4.5 is achieved for such types of epitaxial structure with SCF and substrate thicknesses of 17 μm and about 0.5 mm, respectively. The development types of composite scintillators can be successfully applied for simultaneous registration of α-particles and γ-quanta in the mixed radiation fluxes.

Monthly averages of diurnal temperature variation from meteor radar at Cachoeira Paulista (22.7°S, 45°W), Brazil

Monthly averages of the superposed values of decay times of meteor echoes from underdense meteor trails obtained by meteor radar observations at Cachoeira Paulista (22.7°S, 45°W), Brazil, have been employed to estimate temperature and to study the diurnal temperature fluctuations in the upper mesosphere and lower thermosphere region. The monthly diurnal amplitudes and phases in meteor radar temperatures at Cachoeira Paulista are comparable to those of the westward migrating diurnal tide, with zonal wave number 1, found in the reported temperatures obtained from SABER data, when the observations were obtained during the same period. The diurnal amplitudes in the temperature do not show the semiannual oscillation present in those of the diurnal tide in zonal and meridional winds. The diurnal temperature peaks 4 to 5 h ahead of diurnal tide in the zonal winds and is in anti-phase with the diurnal tide in the meridional winds. The semidiurnal amplitudes of the radar temperature fluctuations also are comparable with SABER westward migrating semidiurnal tide, with zonal wave number 2, and do not present a defined seasonal behavior, while their phases undergo small changes. They lead the semidiurnal tide in the zonal winds by about 4 h during austral summer, but it remains in-phase for the other months, and lead in meridional winds by about 5 to 8 h.

Metal Halide Scintillators with Fast and Self‐Absorption‐Free Defect‐Bound Excitonic Radioluminescence for Dynamic X‐Ray Imaging

AbstractScintillators for radiation detection are of great significance in medical imaging, security, and nondestructive inspection. The current challenge for scintillators is to simultaneously achieve high scintillation light yield, fast radioluminescence, simple film fabrication, large X‐ray attenuation efficiency as well as stable and nontoxic compositions; no previous scintillators fulfill all the above requirements. Here, metal halide Rb2AgBr3, possessing defect‐bound excitonic radioluminescence, is shown as efficient and fast scintillators. This nontoxic and stable scintillator emits from excitons bound to neutral bromine vacancies, enjoying an efficient and spin‐allowed fast emission with minimized self‐absorption. Rb2AgBr3 thus has a high light yield (25 600 photons MeV−1), fast scintillation decay time (5.31 ns), and a record value of light yield versus decay time (4821 photons MeV−1 ns−1). The close‐space sublimation method is developed for fast and scalable fabrication of oriented Rb2AgBr3 films. The scintillator film is further integrated with commercial flat‐panel imagers, and the spatial resolution reaches 10.2 line pairs per millimeter at the modulation transfer function of 0.2, doubling the resolution of conventional CsI:Tl flat‐panel detectors. The dynamic X‐ray imaging and its use to real‐time monitoring of bone movement without ghosting effect is also demonstrated.

New red-emitting Li3Bi3Te2O6:Eu3+ phosphors with high color purity for white light-emitting diodes

This work is the first to synthesize the red-emitting Li3Bi3Te2O6 phosphors using the conventional high-temperature solid-state reaction. The phase purity, particle morphology, and luminescent properties are analyzed in detail. Upon the near-ultraviolet (n-UV) excitation on 395 nm, Li3Bi3Te2O6:Eu3+ phosphors show four emission peaks due to 5D0 → 7FJ (J = 1, 2, 3, 4) transitions and the strongest peak is at 610 nm (5D0 → 7F2). The best doping concentration of Eu3+ ions is found to be 0.45 mol. The critical transfer distance (Rc) of the energy transfer between the Eu3+ ions reaches 11 A and the luminescence quenching is confirmed by the nearest-neighbor ions interaction. The commission international de l'Eclairage (CIE) chromaticity coordinates (0.655, 0.344) of Li3Bi3Te2O6:0.40Eu3+ phosphors are in the red region. The values of decay time are calculated in the millisecond time range from 0.878 to 0.493 ms. Phosphors show common thermal stability with activation energy (0.25 eV). All the properties indicate that Li3Bi3Te2O6:Eu3+ phosphors have potential applications in displays and photonic devices.

Synthesis, structural and optical characterization of Nd: YAG powders via flame spray pyrolysis

In this study, undoped Y3Al5O12 (YAG) and neodymium (Nd3+) doped (Nd: YAG) powders were synthesized by Flame Spray Pyrolysis (FSP) for the first time in literature. The synthesized powders were investigated about structural, morphological, elemental and optical properties by using Thermogravimetric - Differential Thermal Analysis (DTA-TG), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transformed Infrared Spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The particle size range of undoped and Nd doped YAG powders produced by the FSP method was determined around 200–1100 nm. After calcination at 1000 °C, cubic YAG crystalline phases were successfully observed. The luminescence results as excitation, emission, and upconversion properties have been investigated for both undoped YAG (YG) and Nd3+ doped YAG with different dopant ratios as 1% (YG1), 3% (YG3) and %5 (YG5). When synthesized powders excited at 460 nm, the emission maxima observed at 540 nm and 808 nm. All YAG powders yielded bi-exponential decay curves. The highest decay time value was 1% Nd: YAG particle at 277 μs. Furthermore, these powders exhibited upconversion luminescence at lower wavelengths and higher energies when excited at 808 nm.

Laser-induced thermal emission of rough carbon surfaces

The decay of thermal emission of rough surface layers of different carbon materials under the pulsed laser excitation is analyzed both theoretically and experimentally. For pulsed laser heating of rough surfaces, computer simulations revealed that laser-induced thermal radiation is mainly emitted by peaks of the surface relief, and the emission decay time depends on the relation between the laser penetration depth and the temperature diffusion length. It is also concluded that the presence of surface roughness can significantly increase the emission decay time. In the experiments, carbon materials with different thermal characteristics were used; however, all of the investigated samples demonstrated close values of the emission decay time. This fact shows that the material's characteristics on the peaks of surface relief are similar for different carbon materials at high temperature.

Liquid phase epitaxy growth of high-performance composite scintillators based on single crystalline films and crystals of LuAG

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.