Light Output Research Articles

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared.

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Performance improvement of blue light micro-light emitting diodes (< 20 μm) by neutral beam etching process

In this study, micro-light emitting diodes array (μLEDs) with dimensions of 5 μm and 15 μm chip size were fabricated using Neutral Beam Etching (NBE) processes. Size-dependent issues of μLEDs processed by traditional inductively coupled plasma-reactive ion etching (ICPRIE) were alleviated by NBE technology, which exhibited lower equivalent resistance, turn-on voltage, and Ideality factor as compared with those of μLEDs by ICPRIE. Additionally, higher light output power of μLEDs processed by NBE with both 5 μm and 15 μm resulted in higher EQE 7.6 % and 7.7 % than those of μLEDs processed by ICPRIE. Furthermore, the size effect led to a decrease in EQEmax values of the ICPRIE sample by 0.4 %, but only a 0.1 % decay in NBE. Overall, samples fabricated by the NBE process exhibited superior optoelectronic characteristics. Finally, non-radiative recombination behaviors on the mesa sidewall were verified by cathodoluminescence analysis, showing significant decay in ICPRIE samples but not in NBE samples. These results demonstrated the potential of the NBE process for fabricating small chip sizes blue-light μLEDs required for high-brightness, high-efficiency, and high-resolution μLED displays.

Nonproportionality of NaI(Tl) scintillation detector for dark matter search experiments

We present a comprehensive study of the nonproportionality of NaI(Tl) scintillation detectors within the context of dark matter search experiments. Our investigation, which integrates COSINE-100 data with supplementary γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} spectroscopy, measures light yields across diverse energy levels from full-energy γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} peaks produced by the decays of various isotopes. These γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} peaks of interest were produced by decays supported by both long and short-lived isotopes. Analyzing peaks from decays supported only by short-lived isotopes presented a unique challenge due to their limited statistics and overlapping energies, which was overcome by long-term data collection and a time-dependent analysis. A key achievement is the direct measurement of the 0.87 keV light yield, resulting from the cascade following electron capture decay of 22Na\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {^{22}Na}$$\\end{document} from internal contamination. This measurement, previously accessible only indirectly, deepens our understanding of NaI(Tl) scintillator behavior in the region of interest for dark matter searches. This study holds substantial implications for background modeling and the interpretation of dark matter signals in NaI(Tl) experiments.

Near‐unity broadband emissive hybrid manganese bromides as highly‐efficient radiation scintillators

Near‐unity broadband emissive hybrid manganese bromides as highly‐efficient radiation scintillators

Enhancing the performance of AlGaN-based DUV-LEDs with multifocal laser stealth dicing

In this study, AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) processed via standard laser dicing (SLD) and multifocal laser stealth dicing (MFLSD) were investigated. Adopting the MFLSD technology would generate a roughing surface rather than the V-shaped grooves on the sidewall of 508 × 508 µm2 DUV-LEDs, which would reduce the forward operating voltage and increase the wall-plug efficiency, light output power, and far-field radiation patterns of these devices. In addition, the wavelength shift, far-field patterns, and light-tracing simulation results of the DUV-LEDs processed with SLD and MFLSD were clearly demonstrated and analyzed. Accordingly, it was observed that the MFLSD process provided more possibilities for photon escape to increase the light extraction efficiency (LEE) of DUV-LEDs, thus decreased the wavelength-redshift and junction temperature in DUV-LEDs. These results provide a reference for advanced nano-processing practices implemented during the fabrication of semiconductor devices.

Performance optimization of the neutron sensitive image intensifier used in neutron imaging

Performance optimization of the neutron sensitive image intensifier used in neutron imaging

Cold-Sintered All-Inorganic Perovskite Bulk Composite Scintillators for Efficient X-ray Imaging.

Cost-effective bulk scintillators with high density, large-area, and long-term stability are desirable for high-energy radiation detections. Conventional bulk polycrystalline or single-crystal scintillators are generally synthesized by high-temperature approaches, and it is challenging to realize simultaneously high detectivity/responsivity, spatial resolution, and rapid time response. Here, we report the cold sintering of bulk scintillators (at 90 °C) based on an "emitter-in-matrix" principle, in which emissive CsPbBr3 nanocrystals are embedded in a durable and transparent Cs4PbBr6 matrix. These bulk scintillators exhibit high light yield (33,800 photons MeV-1), low detection limit (79 nGyair s-1), fast decay time (9.8 ns), and outstanding spatial resolution of 8.9 lp mm-1 to X-ray radiation and an energy resolution of 19.3% for γ-ray (59.6 keV) detection. The composite scintillator also shows exceptional stability against environmental degradation and cyclic X-ray radiation. Our results demonstrate a cost-effective strategy for developing perovskite-based bulk transparent scintillators with exceptional performance and high radioluminescence stability for high-energy radiation detection and imaging.

Crystal growth, physical and optical properties of TlSr2Cl5 and TlSr2Br5

Small diameter (Ø 16 mm) TlSr2Cl5 and TlSr2Br5 crystals were grown by the Vertical Bridgman method. X-ray diffraction measurements show that both have the monoclinic crystal structure with space group P21/c. TlSr2Cl5 and TlSr2Br5 have a density of 4.14 g/cm3 and 5.03 g/cm3, respectively. The effective Z of TlSr2Cl5 and TlSr2Br5 is 63.7 and 58.6, respectively. Radioluminescence spectra of TlSr2Cl5 and TlSr2Br5 feature a broad emission band peaking at 440 and 445 nm, respectively. The light yield of TlSr2Cl5 and TlSr2Br5 was estimated to be 17,000 and 45,000 ph/MeV, respectively.

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators.

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals show promise as scintillating materials for wide-energy radiation detection, outperforming their three-dimensional counterparts. In this study, we synthesized single crystals of (PEA2-xBZAx)PbBr4 (x ranging from 0.1 to 2), utilizing phenethylammonium (C6H5CH2CH2NH3+) and benzylammonium (C6H5CH2NH3+) cations. These materials exhibit favorable optical and scintillation properties, rendering them suitable for high light yield (LY) and fast-response scintillators. Our investigation, employing various techniques such as X-ray diffraction (XRD), photoluminescence (PL), time-resolved (TR) PL, Raman spectroscopy, radioluminescence (RL), thermoluminescence (TL), and scintillation measurements, unveiled lattice strain induced by dual-organic cations in powder X-ray diffraction. Density functional theory analysis demonstrated a maximal 0.13 eV increase in the band gap with the addition of BZA cation addition. Notably, the largest Stokes shift of 0.06 eV was observed in (BZA)2PbBr4. The dual-organic cation crystals displayed >80% fast component scintillation decay time, which is advantageous for the scintillating process. Furthermore, we observed a dual-organic cations-induced enhancement of electron-hole transfer efficiency by up to 60%, with a contribution of >70% to the fast component of scintillation decay. The crystal with the lowest BZA concentration, (PEA1.9BZA0.1)PbBr4, demonstrated the highest LYs of 14.9 ± 1.5 ph/keV at room temperature. Despite a 55-70% decrease in LY for BZA concentrations >5%, simultaneous reductions in scintillation decay time (12-32%) may work for time-of-flight positron emission tomography and photon-counting computed tomography. Our work underscores the crucial role of dual-organic cations in advancing our understanding of 2D-HOIP crystals for materials science and radiation detection applications.

Optical Information Encryption Based on Secret Sharing Liquid Crystal Elements with Spatial Dislocation

AbstractOptical encryption is an increasingly significant technique in the realm of information security. In the recent decade, there has been considerable interest in using planar optics elements for information encryption. However, information leakage possibly occurs due to limited encrytion channels available for single‐layer devices. To circumvent this problem, a novel encryption method is put forward using secret sharing cascaded liquid crystal (LC) elements with spatial dislocation, which can produce near‐field patterns and far‐field holographic images under different illumination conditions. Specifically, Malus's Law and its inherent one‐to‐four mapping of rotational degeneracy, along with the Pancharatnam‐Berry (PB) phase introduced by LC molecules, to achieve multi‐channel encryption are utilized. Therefore, each cascaded LC unit can manipulate the amplitude and phase imparted to output light independently, thus only by obtaining both LC devices can decryption be realized. To further enhance the encryption security, the author purposely divide each LC device into multiple regions and find that the encrypted patterns can only be recovered when the two LC elements align precisely with a specific dislocation. These experimental measurements agree well with the design, thus demonstrating the strong encryption capability and broad application prospects of the design approach in the field of optical encryption with high cost‐effectiveness.

Catalytic upgrading of Naomaohu coal pyrolysis volatiles over NiAl and NiLiAl oxides

Catalytic upgrading of volatiles is an essential technology to improve the product distribution of pyrolysis for the clean and efficient utilization of low-rank coals. In this work, novel acid-base bifunctional catalysts composed of Ni/Li/Al oxides were designed and prepared using LDH precursors with tunable chemical composition and structural properties. The catalysts were systematically characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), physisorption, NH3-temperature programmed desorption (NH3-TPD), CO2-temperature programmed desorption (CO2-TPD), H2-temperature programmed reduction (H2-TPR), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). A two-stage fixed bed reactor was employed to evaluate the performance of the catalysts. Characterization results suggest that the crystal size of NiO and the surface area of the catalyst decreased with increasing Li content and decreasing Ni content in the catalyst, while the pore volume and pore diameter were positively correlated with Li content. Moreover, the addition of Li reduced the amount of weak acid sites and raised the amount of total basic sites. Consequently, the bifunctional catalysts boosted the yield of light tar and the contents of aromatics and phenols in tar. Specifically, with the highest total acid sites (569 μmol/g) promoting the cracking of heavy pitch components, Ni2.5Li0.5Al1 decreased the content of pitch in tar to 23.8 wt%, representing a 42.7 % drop from the corresponding non-catalytic pyrolysis. Accordingly, it improved the light tar yield to 7.2 wt%, which was 18 % higher than non-catalytic pyrolysis. 450 °C is identified as a suitable temperature for the catalytic upgrading of volatiles from Naomaohu coal; higher catalysis temperatures at 500 °C and 550 °C led to lower tar yield and lower phenols content, along with higher gas yield and more carbon deposition.

Enabling pulse shape discrimination with commercial ASICs

Fast electronic readout for high-channel density scintillator-based systems is needed for radiation tracking and imaging in a wide range of applications, including nuclear physics, nuclear security and nonproliferation. Programmable electronics, like FPGAs and ASICs, provide a fast way of conditioning and processing the signal in real time. In this paper, we present a pulse shape discrimination (PSD) method based on the shaping circuit of a commercially available ASIC, the Citiroc1A by CAEN Technologies. We used two different shaping times per detector channel to calculate a shaping parameter that enables PSD. Using our new method, neutron and gamma-ray pulses detected by a d12-stilbene scintillator can be effectively discriminated at light output values greater than 0.15MeVee. While not achieving the PSD performance of traditional offline charge integration, our method does not require the transfer of data to a separate system for further processing and enables the direct deployment of high-channel density multi-particle detection systems. Moreover, the availability of a wider range of shaping times than those on the Citiroc1A can potentially further improve the PSD performance.

Performance of a first full-size WOM-based liquid scintillator detector cell as prototype for the SHiP Surrounding Background Tagger

As a prototype detector for the SHiP Surrounding Background Tagger (SBT), we constructed a cell (120 cm × 80 cm × 25 cm) made from corten steel that is filled with liquid scintillator (LS) composed of linear alkylbenzene (LAB) and 2,5-diphenyloxazole (PPO). The detector is equipped with two Wavelength-shifting Optical Modules (WOMs) for light collection of the primary scintillation photons. Each WOM consists of an acrylic tube that is dip-coated with a wavelength-shifting layer on its surface. Via internal total reflection, the secondary photons emitted by the molecules of the wavelength shifter are guided to a ring-shaped array of 40 silicon photomultipliers (SiPMs) coupled to the WOM for light detection. The granularity of these SiPM arrays provides an innovative method to gain spatial information on the particle crossing point. Several improvements in the detector design significantly increased the light yield with respect to earlier proof-of-principle detectors. We report on the performance of this prototype detector during an exposure to high-energy positrons at the DESY II test beam facility by measuring the collected integrated yield and the signal time-of-arrival in each of the SiPM arrays. The resulting detection efficiency and reconstructed energy deposition of the incident positrons are presented, as well as the spatial and time resolution of the detector. These results are then compared to Monte Carlo simulations.

The temperature dependent optical and scintillation characterisation of Bridgman grown CsPbX[formula omitted] (X = Br, Cl) single crystals

Lead halide perovskites are reportedly a very promising group of materials for scintillation due to their fast sub-nanosecond exciton luminescence, small band-gaps, and high theoretical light yield. Unfortunately, they only show emission at cryogenic temperatures. In this work single crystals of CsPbBr3 and CsPbCl3 are studied at cryogenic temperatures. Upon comparing the 10 K emission spectra measured under X-ray and UV–vis excitation, a new near-infrared emission was found for both CsPbBr3 and CsPbCl3 only present under X-ray excitation. The integral light yields of CsPbBr3 and CsPbCl3 at 10 K are estimated to be 34,000 and 2,200 photons/MeV under 40 keV X-ray excitation, respectively. The main components of the light yield of CsPbBr3 at 10 K are the near band-gap free exciton emission that suffers from self-absorption and the broad near-infrared emission that falls outside the typical detection range of a photo-multiplier tube. Due to the combination of the two aforementioned effects it was not possible to measure a γ-ray pulse height spectrum for CsPbBr3 at 10 K. Despite all the suitable properties, like the fast decay, a small band-gap, and the positive prospects of 3D perovskite based scintillators, we conclude that these materials perform poorly as scintillation crystals.

High performance deep-ultraviolet light-emitting diodes with transverse electron injection

Conventional structure deep-ultraviolet light-emitting diodes (DUV-LEDs) at short wavelengths typically suffer from electron overflow and low light-emitting efficiency. For solar-blind communication application, conventional DUV-LEDs are struggling to simultaneously implement high external quantum efficiency (EQE) and high modulation bandwidth. In this paper, we report that transverse structure LEDs can overcome abovementioned problems and achieve high EQE and high modulation bandwidth. The n-AlGaN free transverse structure LEDs have been demonstrated to yield high crystal quality multiple quantum wells (MQWs). Due to the transverse electron injection, transverse structure LEDs can confine electrons well within the MQWs and avoid electron overflow. To enhance the electron injection and light extraction characteristics, the narrow and long mesa designs were optimized by both experimental and theoretical-fit results. Finite-difference time domain simulation indicates that the n+-GaN layer of the transverse LEDs with the transverse MQWs mesa design does not degrade light extraction. The transverse structure LEDs attain the maximum light output power and EQE recorded to date for DUV-LEDs below 250 nm, respectively 14 mW and 1.72 %. Furthermore, the −3 dB modulation bandwidth can be achieved up to 416 MHz.

Reactor neutrino physics potentials of cryogenic pure-CsI crystal

AbstractThis paper presents a world-leading scintillation light yield among inorganic crystals measured from a 0.5 kg pure-CsI detector operated at 77 Kelvin. Scintillation photons were detected by two 2-inch Hamamatsu SiPM arrays equipped with cryogenic front-end electronics. Benefiting the light yield enhancement of pure-CsI at low temperatures and the high photon detection efficiency of SiPM, a light yield of 30.1 photoelectrons per keV energy deposit was obtained for X-rays and $$\gamma $$ γ -rays with energies from 5.9 to 59.6 keV. Instrumental and physical effects in the light yield measurement are carefully analyzed. This is the first stable cryogenic operation of kg-scale pure-CsI crystal readout by SiPM arrays at liquid nitrogen temperatures for several days. The world-leading light yield opens a door for the usage of pure-CsI crystal in several fields, particularly in detecting the coherent elastic neutrino-nucleus scattering of reactor neutrinos. The potential of using pure-CsI crystals in neutrino physics is discussed in the paper.

Luminescence and scintillation properties of fast Ce,Mg:Lu2YGaxAl5-xO12 ceramic scintillators fabricated from co-precipitated powders

Ce,Mg:Lu2YGaxAl5-xO12 (x = 1.5, 2, 2.5, 3) ceramic scintillators were fabricated by oxygen sintering combined with air annealing using nano-powders synthesized by the co-precipitation method. The Ce3+ 5d1 → 4f (2F5/2, 2F7/2) luminescence band was blue shifted with increasing Ga content due to the decrease in the crystal field splitting of the 5d levels. At room temperature (RT), the decrease of photoluminescence decay time and scintillation decay time was observed with increasing Ga content. At 662 keV γ-rays, the sample Ga2 exhibited high light yield (LY) of 28,700 photons/MeV, fast scintillation decay times of 17.7 ns (17 %) + 45.7 ns (83 %), and good time resolution of ∼220 ps. At RT, the decrease of LY value for the samples Ga2.5 and Ga3 could be attributed to the larger thermal ionization of the excited Ce3+ centers.

Ce3+ and Cr3+ co-activated ultra-wide visible-NIR garnet phosphor for phosphor-converted light emitting diode

In the past decade, the near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) and NIR phosphors has made considerable progress. However, for the field of non-destructive testing, ultra-wide Vis-NIR pc-LED light source can detect a wider range of components compared to NIR pc-LED. Therefore, the development of high-performance ultra-wide Vis-NIR phosphors is quite necessary. Based on the CaLu2Mg2Si3O12 (CLMSO):Cr3+ with excellent performance, this article proposes the introduction of activator Ce3+ into CLMSO:Cr3+ phosphor, which significantly increase the emission band-width. Co-doped phosphor exhibit excellent thermal stability (maintain 75 % room temperature intensity @ 150 °C). The Vis-NIR light output power can reached 64.4 mW @ 100 mA and 60.9 mW@ 100 mA for pc-LED fabricated with CLMSO:0.01Ce3+, 0.001Cr3+ and CLMSO:0.01Ce3+, 0.002Cr3+ with the electricity to Vis-NIR conversion efficiency reached 30.5 %@10 mA and 29.5 % @10 mA, respectively. The CLMSO: Ce3+, Cr3+ phosphor is expected to become the new generation light sources for miniaturized spectrometer.

Coke formation on different metal-modified (Co, Mo and Zr) ZSM-5 in the catalytic pyrolysis of cellulose to light aromatics

Catalytic pyrolysis of biomass is regarded as a promising method for preparing value-added products. However, the main factors limiting the development of the process at present are the low yield of value-added products and poor selectivity, especially for rapid catalyst deactivation due to coke deposition. The present study focuses on the catalytic pyrolysis of cellulose over metal Co-, Mo-, and Zr-loaded catalysts using a falling fixed bed at 600 °C to evaluate the type of coking of the catalysts as well as the effect of the different metal active sites on the formation of coke deposits. The introduction of Co and Mo metal sites increased the light aromatics yield of ZSM-5 from 128.9 mg/g to 147.2 mg/g and 143.0 mg/g. And the yield of coke deposits decreased from 8.3 to 6.8 and 5.1 wt%. The stability evaluation of the catalyst showed that the deactivation degree of ZSM-5 of the supported metal Co was lower than that of commercial ZSM-5, while the ZSM-5 of the supported metal Mo was rapidly deactivated. The deactivation of the catalysts depended more on the morphology or location of the accumulated coke than on the total amount deposited. The clogging of metal and acidic sites on the surface of the zeolite and the pore channels by the amorphous encapsulating coke was the main cause of catalyst deactivation. The metal Mo active sites promoted dehydrogenation coupling and hydrogen transfer during coke formation, forming a more highly disordered multiring structure, and the metal Co active sites were more capable of decomposing macromolecular compounds, olefins and alkanes, and promoted the formation of graphite-like structural carbon.

Low‐Dimensional Metal Halide for High Performance Scintillators

AbstractInorganic scintillators play a pivotal role in diverse fields like medical imaging, nondestructive detection, homeland security, and high‐energy physics. However, traditional inorganic scintillators encounter challenges such as high fabrication costs and low light yield. Recently, low‐dimensional metal halide scintillators (LDMHS) have witnessed rapid progress, owing to their distinctive crystal structure and superior radioluminescence performance. Herein, an overview of recent advancements and proposed instructive pathways for achieving high‐performance LDMHS is provided. First, the scintillation physical mechanism and emphasis on the essential requirements of scintillators for diverse applications are elucidated. Furthermore, LDMHS by the B‐site, introducing recent advancements and providing insights into their characteristics is categorized. This encompasses the understanding of structure‐property relationships and the routes and rules for optimizing scintillation performance. Finally, the persisting challenges in this burgeoning field and proposed potential research directions for future exploration are discussed.