Short Decay Time Research Articles

Luminescent and Scintillation Properties of LiLu(PO3)4:Pr3+Nanophosphor

Background: Recent advancements in luminescent materials have drawn significant interest due to their wide-ranging applications in radiation detection, lighting, and display technologies. Praseodymium-doped phosphates, in particular, have shown promise because of their unique luminescent and scintillation properties. Objective: This study aims to synthesize, characterize, and evaluate the luminescent and scintillation properties of praseodymium-doped polyphosphate LiLu(PO3)4, focusing on the potential applications of these materials. Methods: LiLu(PO3)4:Pr3+ microcrystals were synthesized using the flux method, while nanocrystals were produced via the coprecipitation technique. The synthesized polyphosphates were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Results: LiLu(PO3)4:Pr3+ crystals were found to crystallize in the monoclinic C2/c space group with specific lattice parameters. The structural analysis revealed that the basic units are helical ribbons of (PO3)n formed by corner-sharing PO4 tetrahedra, with LuO8 dodecahedra and LiO4 tetrahedra forming linear chains. The incorporation of praseodymium ions resulted in the observation of both ultraviolet and visible luminescence under X-ray and laser excitations. UV emission, originating from 4f-5d → 4f2 transitions, exhibited a very fast lifetime (τ4f-5d = 3 ns), while visible emission from transitions within the Pr3+ 4f2 ground configuration showed a short decay time of approximately 100 ns. Conclusion: The scintillation properties of LiLu(PO3)4:Pr3+ demonstrated promising results, indicating their potential for various high-performance applications, including solid-state lighting, bioimaging, and radiation detection.

The role of BaTiO3 nanoparticles as photocatalysts in the synthesis and characterization of novel fruit dyes is investigated.

In the present work, the photocatalytic activity against the natural dye extracted from the novel fruits has been studied by the BaTiO3 nanoparticles (NPs) under a ultra-violet (UV) light source. The large concentrations of an essential phenolic agent present in this phytochemical extract superimposed with cloths fibers make strong stain and degrade into another form of toxic, which is excluded from the many textiles industries as the colorful waste waters without recycling and removal of that dye pigments have been investigated using both photodegradation and photoluminescence techniques. The entitled nanoparticles (NPs) were prepared using the soft chemical root-modified solvothermal synthesis combo method and exposure to heat treatment such that the annealing process has been done for different temperatures ranging from 100°C to 250°C. As for as concern the characterization, as a start, structural and morphology studies have been reported here that highly crystalline oriented peaks data using powder x-ray diffraction techniques (PXRD) as well as the surface morphology including the size, shape, and mass distribution using the field emission scanning electron microscopy (FESEM) techniques, which purely belong to rutile tetragonal structure of the crystal system and circular and noncircular flakes like rough surface morphology materials respectively. The lattice dissociation constant 'ε' value of the BaTiO3 NPs has determined to be ~2.71 × 10-3 using the Williamson-Hall (W-H plot) analysis of crystallographic data. In the UV visible spectroscopy findings, since the extreme quantum confinement of BaTiO3 nanoflakes/nanodisc, the optical energy bandgap has been estimated to be a range of 1.98 to 2.67 eV (~2.48 eV) found from the Tauc plot analysis, which contributes to the significantly owing to the enhanced photocatalytic efficiency with excellent performance along exciton formation, superoxide ions, and hydroxyl free radicals generations under UV-vis light irradiation resulting in efficient degradation of typical novel fruit organic dye. Photoluminescence spectra observed at room temperature and low temperature have been observed for the BaTiO3 nanoflakes, which exhibit the blue emission due to the crystalline defects such as the appearance of Ba vacancies leads to the conceivable beginning of p-type conductivity and the origination of free exciton emission reveals the direct bandgap transition nature of nanoflakes. RESEARCH HIGHLIGHTS: According to our findings, 89.71% of the natural syzygium cumin is degraded by photocatalysis reaction. As a plausible mechanism for the destruction of natural dyes under solar light, photocatalytic destruction has been proposed. The reaction between these reactive free radical species leads to high efficiency photodegradation with a short decay time. In addition to water treatment and environmental cleaning applications, the excellent performance of this photocatalyst makes it a promising candidate for other applications. Hence, the synthesized BaTiO3 nanoflakes showcase a highly significant advancement towards the development of a textiles dye recycling method.

Cerium doped yttrium aluminum perovskite scintillator as an absolute ultracold neutron detector.

The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the beta decay rate of free neutrons with different systematic uncertainties than previous beam-based neutron lifetime experiments. We have tested a new 10B-coated Yttrium Aluminum Perovskite (YAP:Ce) scintillator and present its properties. The advantages of the YAP:Ce scintillator include its high Fermi potential, which reduces the probability for upscattering of ultracold neutrons (UCN), and its short decay time, which increases sensitivity at high counting rates. Birks' coefficient of YAP:Ce was measured to be (5.56-0.30+0.05)×10-4 cm/MeV. The loss of light due to the 120nm 10B-coating was measured to be about 60%, and the loss of light from YAP:Ce due to transmission through a deuterated polystyrene scintillator was about 50%. The efficiency for neutron capture on the 10B coating was (86.8 ± 2.6)%, and a measurement using UCN showed that the YAP:Ce crystal counted 8%-28% more UCN compared to a ZnS:Ag screen. The difference may be due to the uneven coating of 10B on the rough surface of ZnS:Ag.

Enhanced luminescence encryption via Mn4+ activation with organic acid surface modification

Mn4+-activated luminescent materials exhibit high color purity red light emission, but their limited water resistance hinders practical applications. In this study, citric and oxalic acids are innovatively employed for surface modification, resulting in luminescent materials with enhanced water resistance while preserving their luminescent intensity. This enhancement provides a prerequisite for their application in anti-counterfeiting films and aqueous fluorescent inks. Furthermore, the potential for optical information storage is successfully demonstrated by utilizing the photochromic fluorescent properties of polyvinyl alcohol films deposited on oxalic acid-modified K2SiF6:Mn4+. Exploiting the 3 ms day time difference between equivalently and non-equivalently doped Mn4+ fluoride, a millisecond information encryption mode is proposed by combining oxalic acid-modified K2SiF6:Mn4+ (long decay time, τ = 8.99 ms) and K3AlF6:Mn4+ (short decay time, τ = 5.31 ms). This mode can be effectively decoded using digital cameras and editing software, achieving high-level anti-counterfeiting capabilities. This work advances the application of highly efficient Mn4+-activated red phosphors in the realm of information security.

Unveiling the Carrier Dynamics of Perovskite Light-Emitting Diodes via Transient Electroluminescence.

Perovskite light-emitting diodes (PeLEDs) have garnered significant attention due to their outstanding optoelectronic properties. However, investigating carrier transport and recombination behavior during device operation poses persistent challenges. In this study, we explore the impact of additive and interface engineering on device performance using transient electroluminescence (TREL). Polyethylene glycol (PEG) induces the formation of square-faceted nanocrystals with a homogeneous size distribution and extended fluorescence lifetime. Consequently, these PeLEDs exhibit remarkable stability. Additionally, employing an electron transport layer of 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine (PO-T2T), which has a better match to the energy bands of the perovskite layer and a higher carrier mobility, allows for lower turn-on voltage and faster response but also suffers from a short decay time and poor stability. Moreover, low-temperature TREL characterization shows that the carrier mobility is also significantly suppressed with decreasing temperature, which reduces the transient response speed.

Cu2O/TiO2 core–shell nanowire heterojunction for high-performance self-powered photodetector

High-performance self-powered photodetectors (PDs) have great commercial value in optical communication, intelligent sensing and medical diagnosis. However, the limited active area of traditional thin film heterojunction seriously restricts the photoelectric performance of the detector. In this paper, the Cu2O/TiO2 core-shell nanowire (NW) heterojunction PD was synthesized for the first time by simple hydrothermal and electrochemical deposition methods, which effectively improved the response performance and response speed of the device based on its broad photoactive area and ordered carrier transport path. The PD exhibits significant diode behavior, with rectification ratios of 543 at ±2 V. The responsivity is as high as 6.8 mA W−1 at zero bias under 490 nm illumination. The short rise and decay times measured are 0.09 and 0.18 s at zero bias, respectively. Obviously, this low-cost, high-performance self-powered Cu2O/TiO2 core-shell NW heterojunction PD shows great promise in future optoelectronic device applications.

Photoacoustic Image Analysis of Dental Tissue Using Two Wavelengths: A Comparative Study

This work compares photoacoustic images of a tooth by analyzing the signals generated with wavelengths 532 and 355 nm. This comparison addresses the differences in the optical properties of dental tissue for these wavelengths that affect the resulting photoacoustic images. A pulsed Nd:YAG laser was used to illuminate a complete extracted tooth sample, and 2D photoacoustic images (PAIs) were reconstructed using the single-sensor scanning synthetic aperture focusing technique (SSC-SAFT), which is a suitable method for our experimental system with forward detection mode. Signal comparison was conducted using sinogram, signal-to-noise ratio (SNR), root mean square (RMS), arrival time, maximum amplitude, and fast Fourier transform (FFT). PAI comparison utilized intensity profile, edge correlation, and image composition tools. The signal analysis revealed that at 532 nm, the signals exhibited longer decay time and a wider distribution of vibration frequencies due to higher laser pulse energy and greater optical penetration depth. Conversely, at 355 nm, the signals had shorter decay times and a lower frequency distribution, which was attributed to lower energy but improved optical absorption, resulting in reconstructed images with better sharpness and contour definition. This study contributes to the advancement of photoacoustic imaging technology in dentistry by providing insights that could optimize signal generation and image reconstruction for dental tissue.

Comparing the Luminescence and Moisture Resistance of K3AlF6:Mn4+ Phosphor to Commercial Phosphors

Nowadays, red-emitting phosphors based on Mn4+ doped fluorides with a high color purity and a relatively short decay time can improve the optical performance of WLED. However, they are easily oxidized in humid environment and elevated temperatures. This is the reason why both the brightness and luminous efficiency of WLED quikly decreased. To solve this problem, KF was added throughout the K3AlF6:Mn4+ phosphor synthesis process (KKAFM). This work is focused on aging evaluation of the phosphors and comparing its performance with commercial phosphors (YAG:Ce3+, Sr2Si5N8:Eu2+). Thus, EL spectra of blue LED chips coated with the phosphors were investigated over time in an environment of 85 % RH and 85 oC. The results of EL spectra showed the improvement in the the reduction of the emission intensity of KKAFM. Aging tests of WLEDs using KKAFM and Sr2Si5N8:Eu2+ indicated that KKAFM phosphors exhibited a good stability, thus they can be used as a potential replacement for commercial red-emitting phosphors in WLEDs fabrication.

Luminescence of CsLa1-хCeхSiS4 thiosilicate solid solution: From STE to Ce3+ emission

A series of single crystals of CsLa1-хСехSiS4 monophasic solid solution (x = 0–1) has been obtained for the first time by high-temperature flux synthesis. Methods of XRD and chemical analysis, absorption and low-temperature (from T = 5 K) luminescent spectroscopy were used. The results of the band scheme calculating using density functional theory correlate with spectroscopy data. One non-elementary d → f emission band of Ce3+ ions is observed in the region of 520 nm in the luminescence spectra at room temperature at any value of the x parameter. The luminescence decay kinetics of Ce3+ ions upon excitation by a pulsed electron beam, X-ray synchrotron radiation or intracenter photoexcitation is characterized by a nanosecond component. As the parameter x increases, the decay time is reduced from 132 ns (x = 0.005) to 0.88 ns (x = 1). The luminescence decay kinetics upon photoexcitation at x = 0.005–0.12 is characterized by monoexponential decay with τ = 31.4 ± 0.2 ns. Concentration quenching of the Ce3+ ion photoluminescence is not observed up to the value of the parameter x = 0.12; it only appears at x = 1. The anomalously short decay time of the Ce3+ ions luminescence in CsCeSiS4 upon both X-ray excitation and photoexcitation is associated with concentration quenching.At temperature 5 K, new intense bands at 408 and 688 nm in addition to the Ce3+ emission band observed in the photoluminescence spectra of nominally pure CsLaSiS4 or at the lowest parameter value x = 0.005. These bands correspond to the luminescence of self-trapped excitons (STE) and defects. With increasing x parameter, the STE emission band is reabsorbed by the absorption of Ce3+ ions and is quenched due to the resonance energy transfer STE → Ce3+ center. Thermoluminescence glow curves of CsLa1-xCexSiS4 irradiated with X-ray at T = 90 K are characterized by several low temperature intense peaks, which indicates a high concentration of charge carrier traps.

Dual-Schottky-junctions coupling device based on ultra-long β-Ga2O3 single-crystal nanobelt and its photoelectric properties

High quality β-Ga2O3 single crystal nanobelts with length of 2−3 mm and width from tens of microns to 132 μm were synthesized by carbothermal reduction method. Based on the grown nanobelt with the length of 600 μm, the dual-Schottky-junctions coupling device (DSCD) was fabricated. Due to the electrically floating Ga2O3 nanobelt region coupling with the double Schottky-junctions, the current I S2 increases firstly and rapidly reaches into saturation as increase the voltage V S2. The saturation current is about 10 pA, which is two orders of magnitude lower than that of a single Schottky-junction. In the case of solar-blind ultraviolet (UV) light irradiation, the photogenerated electrons further aggravate the coupling physical mechanism in device. I S2 increases as the intensity of UV light increases. Under the UV light of 1820 μW/cm2, I S2 quickly enters the saturation state. At V S2 = 10 V, photo-to-dark current ratio (PDCR) of the device reaches more than 104, the external quantum efficiency (EQE) is 1.6 × 103%, and the detectivity (D*) is 7.5 × 1012 Jones. In addition, the device has a very short rise and decay times of 25−54 ms under different positive and negative bias. DSCD shows unique electrical and optical control characteristics, which will open a new way for the application of nanobelt-based devices.

Highly Sensitive Temperature Sensors Resulting from the Luminescent Behavior of Sm3+-Doped Ba2MgMoO6 High-Symmetry Double-Perovskite Molybdate Phosphors.

We present double-perovskite molybdate with the formula of Ba2MgMoO6 doped with Sm3+ ions as a potential red phosphor to improve the color characteristics of white-light-emitting dioded (wLEDs). The new orange-red phosphor was synthesized using the co-precipitation (CP) method, and then its structural and spectroscopic properties were determined. Red emission at 642.6 nm dominates, which results from the electric dipole (ED) transition of the 4G5/2 → 6H9/2 type, and the materials are characterized by short luminescence decay times. BMM:Sm3+ is, to our best knowledge, the clearest example of dominant red emission of Sm3+ resulting from the location of the dopant in octahedral sites of high-symmetry cubic structure. In the sample containing 0.1% Sm3+, Sm3+ ions are located in both Mg2+ and Ba2+ sites, while at higher concentrations the Ba2+ site is less preferable for doping, as a result of which the emission becomes more uniform and single-site. The relative sensitivity calculated from FIR has a maximum of 2.7% K-1 at -30 °C and another local maximum of 1.6% K-1 at 75 °C. Such value is, to the best of our knowledge, one of the highest achieved for luminescent thermometry performed using only Sm3+ ions. To sum up, the obtained materials are good candidates as red phosphor to improve the color characteristics of wLEDs, obtaining a color-rendering index (CRI) of 91 and coordinated color temperature (CCT) of 2943 K, constituting a warm white emission. In addition to this, a promising precedent for temperature sensing using high-symmetry perovskite materials is the high sensitivity achieved, which results from the high symmetry of the BMM host.

Performance of New Kuraray Wavelength-shifting Fibers with Short Decay Time

Abstract We measure the decay time and the attenuation length of newly developed wavelength-shifting fibers, the YS series, from Kuraray, which have a fast response. Using a 405 nm laser, the decay times of YS-2, 4, and 6 are measured to be 3.64 ± 0.04, 2.15 ± 0.03, and 1.47 ± 0.02 ns, respectively, for a light injection distance of 10 cm. The decay time of Y-11 is measured to be 7.10 ± 0.09 ns using the same system. All fibers are found to have similar attenuation lengths of more than 4 m. When combined with the plastic scintillators EJ-200 and EJ-204, the YS series has better time resolution than Y-11, with light yields of 60–100% of Y-11.

Pulse shape discrimination in an organic scintillation phoswich detector using machine learning techniques

We developed machine learning algorithms for distinguishing scintillation signals from a plastic-liquid coupled detector known as a phoswich. The challenge lies in discriminating signals from organic scintillators with similar shapes and short decay times. Using a single-readout phoswich detector, we successfully identified γ radiation signals from two scintillating components. Our Boosted Decision Tree algorithm demonstrated a maximum discrimination power of 3.02 ± 0.85 standard deviation in the 950 keV region, providing an efficient solution for self-shielding and enhancing radiation detection capabilities.

Copper(I)‐Arsine Clusters with a Near‐Unity Phosphorescence Quantum Yield for X‐Ray Scintillation and LED Applications

AbstractRare‐earth element‐free materials that exhibit strong room temperature phosphorescence (RTP) and X‐ray scintillation properties are gaining global interest incessantly in the recent years. This work reports a series of easily synthesizable cubane Cu4I4‐triarsenic clusters [Cu4I4(R3As)3L] (L = none or nitrile), that exhibit a strong yellow‐green RTP with quantum efficiencies up to 100% and short decay times (4.4–4.9 µs). The title cluster complexes display X‐ray scintillation properties with a record ultralow detection limit (18.1 nGy s−1) and a perfectly linear dose rate response within a remarkably wide dose rate window (0–640 µGyair s−1). The cluster [Cu4I4(Ph3As)3] is highlighted as an efficient phosphor for UV‐pumped white and yellow LED devices, demonstrating an excellent white spectrum with a CIE index of (0.32,0.33) and bright yellow emission, respectively. These results may stimulate the future efforts in designing highly efficient arsenic‐based RTP materials and enriching the Cu4I4 cluster family.

Characteristics of Ce-doped phosphate inorganic glass scintillators for gamma- and X-ray detection

We report on the structural, photoluminescence (PL), and scintillation properties of Ce-doped P2O5–Al2O3–Cs2O–BaO glass scintillators having different Ce concentrations (1.96, 3.85, 7.41, 10.7, and 13.8 mol%) for gamma- and X-ray detection. The highest density (3.57 g/cm3) was achieved with Ce concentration of 13.8 mol%. The PL emission and X-ray-induced radioluminescence spectra showed emission peaks corresponding to the allowed transition from the Ce3+ 5d excited state to the 4f ground states. The highest scintillation light yields (approximately 2200 photons/MeV) were achieved with Ce concentrations of 7.41, 10.7, and 13.8 mol%. These light yields are higher than those previously reported for glasses containing heavy elements, such as Eu-doped SiO2–Al2O3–HfO2 (630 photons/MeV), Ce-doped P2O5–Li2O–GdI3–Al2O3–CaCO3 (1600 photons/MeV), and Ce-doped SiO2–Al2O3–BaF2–Gd2O3 (2050 photons/MeV). For all glasses, short scintillation decay times (28.5–34.0 ns) corresponding to the transition from the Ce3+ 5d excited state to the 4f ground states were observed. These results indicate that the fabricated glass with an optimal Ce concentration of 13.8 mol% is suitable for gamma- and X-ray detection.

Active oscillatory associative memory

Traditionally, physical models of associative memory assume conditions of equilibrium. Here, we consider a prototypical oscillator model of associative memory and study how active noise sources that drive the system out of equilibrium, as well as nonlinearities in the interactions between the oscillators, affect the associative memory properties of the system. Our simulations show that pattern retrieval under active noise is more robust to the number of learned patterns and noise intensity than under passive noise. To understand this phenomenon, we analytically derive an effective energy correction due to the temporal correlations of active noise in the limit of short correlation decay time. We find that active noise deepens the energy wells corresponding to the patterns by strengthening the oscillator couplings, where the more nonlinear interactions are preferentially enhanced. Using replica theory, we demonstrate qualitative agreement between this effective picture and the retrieval simulations. Our work suggests that the nonlinearity in the oscillator couplings can improve memory under nonequilibrium conditions.

Excited state dynamics of Bi3+ centers in cubic Gd2O3

Photoluminescence characteristics of Gd2O3:Bi are studied in the 4.2–800 K temperature range by the time-resolved spectroscopy methods. Purely cubic structure of Gd2O3:Bi is confirmed by XRD. The luminescence of Bi3+(S6) and Bi3+(C2) centers is found to arise from the electron transitions from the emitting level of the triplet excited state of Bi3+, corresponding to the 3P1 → 1S0 transitions of the free Bi3+ ion. Relaxation processes in the triplet excited state of Bi3+ ions do not result in the population of the lowest-energy metastable level. The absence of the radiative transitions, corresponding to the 3P0 → 1S0 transitions of the free Bi3+ ion, explains the short (0.3–2.0 μs) decay time of the triplet emission of Bi3+ even at 4.2 K. The conclusion is made that the fast luminescence decay cannot be caused by the mixing of the metastable and emitting levels of the triplet excited state of Bi3+ by the magnetic field created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. The electron transfer and recombination processes, resulting in the appearance of the photo- and thermally stimulated electron recombination luminescence of Bi3+(S6) and Bi3+(C2) centers under excitation in the Eexc > 4.3 eV energy region, are also discussed. The energy level positions of the Bi3+(S6) and Bi3+(C2) centers in the band gap of Gd2O3 are estimated.

Bicarbazole-Benzophenone-Based Twisted Donor-Acceptor-Donor Derivatives as Blue Emitters for Highly Efficient Fluorescent Organic Light-Emitting Diodes.

This paper delves into the development of a group of twisted donor-acceptor-donor (D-A-D) derivatives incorporating bicarbazole as electron donor and benzophenone as electron acceptor for potential use as blue emitters in OLEDs. The derivatives were synthesized in a reaction of 4,4'-difluorobenzophenone with various 9-alkyl-9'H-3,3'-bicarbazoles. The materials, namely, DB14, DB23, and DB29, were designed with different alkyl side chains to enhance their solubility and film-forming properties of layers formed using the spin-coating from solution method. The new materials demonstrate high thermal stabilities with decomposition temperatures >383 °C, glass transition temperatures in the range of 95-145 °C, high blue photoluminescence quantum yields (>52%), and short decay times, which range in nanoseconds. Due to their characteristics, the derivatives were used as blue emitters in OLED devices. Some of the OLEDs incorporating the DB23 emitter demonstrated a high external quantum efficiency (EQEmax) of 5.3%, which is very similar to the theoretical limit of the first-generation devices.

Synthesis and investigation of novel boron- and magnesium-doped YAG:Ce and LuAG:Ce phosphor ceramics.

YAG:Ce and LuAG:Ce ceramics are widely used as scintillator materials that convert high-energy radiation into visible light. For the practical application of such compounds, short decay times are a necessity. One way of shortening the existing decay times even more is to change the local environment of emitting ions by means of doping the matrix with additional elements, for example, boron or magnesium. Furthermore, boron ions also can help absorb gamma rays more efficiently, therefore improving overall applicability. Due to the aforementioned reasons, YAG and LuAG ceramics doped with cerium, boron, and magnesium were synthesized. Initial amorphous powders have been obtained by means of sol-gel synthesis and pressed into pellets under isostatic pressure and finally calcinated to form crystalline ceramics. The effects of boron and magnesium doping on the morphological, structural, and luminescence properties were investigated. The key results showed that doping with boron has indeed shortened the decay times of the garnet pellets. Overall, boron doping of ceramics is a relatively new research area; however, it is rather promising as it helps both to improve the luminescence properties and to increase particle growth rate.

Liquid crystal/polymer composites for energy-efficient smart windows with a wide working temperature range and low off-axis haze

As a type of intelligent dimming film, polymer dispersed liquid crystal (PDLC) films show attractive application prospects in field of smart windows. However, their current performance cannot meet the requirement of outdoor window applications, especially in severe conditions, such as poor shielding effect at high temperatures, delayed response at low temperatures and high off-axis haze. To simultaneously solve these problems, a PDLC film was prepared by optimizing the structure of acrylate crosslinking agent and birefringence of LC, which exhibits good shielding effects and contrast ratio (10) at high temperature of 100 °C, short rise time (0.16 s) and decay time (2.4 s) at low temperature of −30 °C, and a satisfying low off-axis haze (on-state haze <10 % at ±45°, on-state transmittance >65 % at ±60°). This study provides meaningful supplements for the application of PDLC film in outdoor smart windows, especially in automotive smart windows under extreme weather conditions.