Bright Light Emission Research Articles

Deep learning for in-situ powder stream fault detection in directed energy deposition process

In the directed energy deposition (DED) process, stable powder feeding through nozzles is crucial. However, abnormal powder feeding due to nozzle clogging or adhesion frequently occurs, which can cause severe defects or even lead to a process failure. Nevertheless, the abnormal powder feeding detection is challenging because the powder stream variance is subtle, and the sensing area is under a harsh environment with bright melt pool light emission and spatter ejection. This study proposes the abnormal powder feeding detection method based on a deep learning technique using melt pool images. The trained model by training dataset collected through a coaxial camera with deliberately installed clogged nozzle can discriminate between normal and abnormal states and even classify the fault nozzle among the 4 nozzles installed. The classification performance has a prediction accuracy of up to 99.2%. The result shows that the deep learning technique using melt pool images could be promising for in-situ DED process fault detection.

Size-Controlled Indium Phosphide Quantum Dots for Bright and Tunable Light Emission by Simple Hindered Diamine Addition

Size-Controlled Indium Phosphide Quantum Dots for Bright and Tunable Light Emission by Simple Hindered Diamine Addition

Extrinsic Effects on the Optical Properties of Surface Color Defects Generated in Hexagonal Boron Nitride Nanosheets.

Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission. Using these techniques, we have found that subsequent ozone treatments of the deposited hBN nanosheets improve the optical emission properties of created defects, as revealed by their zero-phonon linewidth narrowing and reduction of background emission. Microlocalized color defects deposited on dielectric substrates show bright (≈1 MHz) and stable room-temperature light emission with zero-phonon line peak energy varying from 1.56 to 2.27 eV, being the most probable value 2.16 eV. In addition to this, we have observed a substrate dependence of the optical performance of the generated color defects. The energy range of the emitters prepared on gold substrates is strongly reduced, as compared to that observed in dielectric substrates or even alumina. We attribute this effect to the quenching of low-energy color defects (these of energies lower than 1.9 eV) when gold substrates are used, which reveals the surface nature of the defects created in hBN nanosheets. Results described here are important for future quantum light experiments and their integration in photonic chips.

GaN-nanopillar-based light-emitting diodes directly grown on multi-crystalline Si substrates

For the first time, light-emitting diodes based on gallium nitride nanopillar crystals were prepared directly on a multi-crystalline silicon substrate, which is widely utilized in low-cost solar cells. Several double-hetero-p–n-junction structures were fabricated, and bright light emission was obtained from the diodes. In addition, white-light emission was observed in another diode. The multi-crystalline Si substrate can be added to a candidate substrate to realize practical, novel, large-area light-emitting devices.

SYSTEM OF PERSON’S VISUAL PERCEPTION AS AN OBJECT OF IMPACT BY LIGHT EMISSION

In modern conditions of hostilities, informativity plays an important role in both defense and offensive operations. Most of the information, including technical, passes through optical systems. Optoelectronic and infrared devices, missile homing heads, the human eye in their structure have optics with different coefficients. A light pulse of different levels makes a negative impact on optical systems decreasing data throughput.
 One of the possible types of impact on personnel in order to disorient enemy troops and disable optical surveillance and sighting systems is the use of light emission. Light emission can negatively affect the system of visual perception and cause the deterioration of information processing efficiency, so it can be used as a factor for the destruction of enemy personnel. In the process of impact by light emission on the system of visual perception, the phenomenon of after-effect is possible. It consists in the process of adaptation of the system of visual perception to the perception of information after exposure to bright light emission. The visual center of the brain plays a major role in the adaptation processes, so a human can see the transitions of the brightness of the adaptive background. The longest adaptation time occurs when exposed to blue and white light. The increase in the area of receptive fields leads to a decrease in the resolving capabilities of the system of visual perception and affects the effectiveness of the combat task in terms of target recognition and sighting.
 The main intense light emission impact factors on the enemy’s personnel are: psychological effect (disorientation and distraction) which is manifested in the temporary cessation of task execution, which relates to the unexpected emergence of bright emission; impairment of visual function (when intense bright light emission blocks the system of visual perception; temporary loss of vision; disorientation and epileptic attacks.

Enhancement of fluorescence and magnetic properties of CeF3:RE3+ (Tb, Gd) nanoparticles via multi-band UV excitation and Li doping regulation

In this study, hydrothermal synthesis of CeF3: Tb, Gd nanoparticles doped with Li+ alkali metal ions were demonstrated using introduction of Li+ ions through LiNO3 nitrate. These nanoparticles have dual properties of magnetic fluorescence. X-ray diffraction, Fourier transform infrared spectrometer, XPS and photoluminescence spectra, and vibrating sample magnetometry were used to characterize structural properties, surface functional groups, fluorescence, and magnetic properties of these particles. Results show that CeF3: Tb, Gd nanoparticles exhibit bright green light emission under excitation at 258 nm and 378 nm ultraviolet band. Through the modification of Li+ ions, luminous intensity of green light is further improved. Energy transfer between rare earth ions was investigated via photoluminescence spectroscopy. This work demonstrates potential applications of Li doped CeF3: Tb, Gd nanoparticles as photomagnetic dual-functional materials in fields of biological imaging, solid state lighting, and magnetic biological separation.

Efficient larger size white quantum dots light emitting diodes using blade coating at ambient conditions

Here, we propose a facile strategy to realize all-solution-processed highly efficient full-color-enabling white emitting quantum dot light-emitting diodes (QLEDs) at ambient conditions by using low-cost blade coating technique, which was also compatible with the roll to roll fabrication process for large size production. Firstly, by using red quantum dots (QDs) as the representative to optimize the QDs films by blade coating, the QDs films exhibit excellent morphology and well-ordered self-assembly structure. Then, the trichromatic white QLEDs based on mixed red, green and blue quantum dots were obtained with Commission Internationale De I'Eclairage (CIE) coordinates ranging from (0.42, 0.41) to (0.31, 0.33) within the white region of CIE 1931 when driving voltage vary from 5 v to 8 v. The device enjoys excellent optoelectronic performance including a maximum luminance of 11,465 cd/m 2 , a maximum current efficiency ( η A ) of 9.2 cd/A and an external quantum efficiency (EQE) of 3.7%. In addition, 3 × 8 cm 2 white QLEDs with bright and homogenous light emission fabricated by blade coating are demonstrated. Our strategy for fabricating large-area white QLEDs indicate promising applications in the low-cost solid-state lighting and flat-panel displays. • The QDs films exhibit excellent morphology and well-ordered self-assembly structure by blade coating. • The trichromatic white QLEDs were obtained with a maximum luminance of 11,465 cd/m 2 , η A of 9.2 cd/A and EQE of 3.7%. • 3×8 cm 2 white QLEDs with bright and homogenous light emission fabricated are demonstrated.

Spatial–temporal evolution of plasma radiation in electrical wire explosion: a morphological observation

This paper deals with an experimental study regarding the spatial–temporal evolution of single wire explosions in air and water at atmospheric pressure. Experiments were carried out with a microsecond timescale pulsed current source under 500 J stored energy. The morphology of the exploding wire with different discharge type, wire material, insulating coat, and ambient medium was intensively observed via self-emission images. The results revealed that the plasma radiation of wire explosion in air mainly contained two stages: initial intense radiation from optically thick plasma, and later decaying radiation from expanded arc-like plasma. A hollow structure was observed in a Cu exploding wire in air, and the plasma channel tended to develop inside it. As for W case, there would always be a core-corona structure, resulting in lower expansion rate and shock wave strength. Moreover, the plasma radiation of the underwater wire explosion was mainly determined by two factors: expansion rate and chemical reaction. The expansion rate of the radiant region in water was only 10–1 mm μs–1 level (1 mm μs–1 level for air), leading to the lagging radiation. No noticeable difference in morphology was found between Cu and W wire explosions in water. Particularly, the Al wire explosion generated a bright light emission due to chemical reactions. Finally, radiative characteristics in an exploding wire were preliminarily concluded and existing problems proposed.

Intense blue emission of perovskite-type fluoride phosphor Cs4Mg3CaF12: Eu2+ as a promising pc-WLEDs material

Abstract An intriguing novel perovskite-type Cs4Mg3CaF12: Eu2+ phosphor with desirable properties for potential application in the field of white light-emitting diodes was first time synthesized. The Rietveld structural refinement, scanning electron microscopy and high resolution transmission electron microscopy were used to determine the crystallographic parameters, morphology and microstructure of Cs4Mg3CaF12: Eu2+ phosphor. The first principle calculation based on the density functional theory further provided a theoretical understanding of the band structure for the undoped Cs4Mg3CaF12 and indicated that it has a large direct band gap of 7.1 eV. Upon the excitation of Cs4Mg3CaF12: Eu2+ phosphor in the broad range of 250–450 nm, the bright blue light emission was observed with the maximum at 474 nm and a full width at half-maximum of 2808 cm−1 that was attributed to the electric-dipole allowed 4f65 d1→4f7 transition of Eu2+ ions. Based on the Dexter’s theory, the concentration quenching mechanism among Eu2+ in the Cs4Mg3CaF12: Eu2+ phosphor was validated to be the dipole-dipole interaction, and the critical distance was determined to be 23.34 A. On the basis of temperature-dependent luminescence measurement, an analysis of the origins of thermal quenching behavior was presented. The Cs4Mg3CaF12: Eu2+ phosphor not only has favorable thermal stability with emission intensity reduction by 20% at T = 473 K in reference to the room temperature level, but also shows the integrated PL intensity 95% as high as that of BaMgAl10O17: Eu2+, internal quantum efficiency of 64% and color purity of 85%. The results of this work indicate that the blue-emitting Cs4Mg3CaF12: Eu2+ phosphor with promising luminescence properties has a capacity for incorporation as a component to the near-UV based phosphor-converted WLEDs.

Highly Luminescent Copper Iodide Cluster Based Inks with Photoluminescence Quantum Efficiency Exceeding 98.

Highly luminescent inks are desirable for various applications such as decorative coating, art painting, and anticounterfeiting, to name a few. However, present inks display low photoluminescent efficiency requiring a strong excitation light to make them glow. Here, we report a highly luminescent ink based on the copper-iodide/1-Propyl-1,4-diazabicyclo[2.2.2]octan-1-ium (Cu4I6(pr-ted)2) hybrid cluster with a quantum efficiency exceeding 98%. Under the interaction between the Cu4I6(pr-ted)2 hybrid cluster and polyvinylpyrrolidone (PVP), the highly luminescent Cu4I6(pr-ted)2/PVP ink can be facilely prepared via the one-pot solution synthesis. The obtained ink exhibits strong green light emission that originates from the efficient phosphorescence of Cu4I6(pr-ted)2 nanocrystals. Attractively, the ink displays high conversion efficiency for the ultraviolet light to bright green light emission due to its wide Stokes shift, implying great potential for anticounterfeiting and luminescent solar concentrator coating.

Uniform and bright light emission from a 3D organic light-emitting device fabricated on a bi-convex lens by a vortex-flow-assisted solution-coating method

We herein present the results of a study on the novel fabrication process of uniform and homogeneous semiconducting polymer layers, in this case hole-injecting and fluorescent light-emitting layers that were produced by a simple solution-coating process for 3D conformal organic light-emitting diodes (3D OLEDs) on curvilinear surfaces. The solution-coating process used was a newly developed method of vortex-flow-assisted solution-coating with the support of spinning of the coating solution. It is shown that the vortex-flow-assisted spin-coating process can produce high-quality thin films at nanoscale thicknesses by controlling the liquid surface of the coating solutions, which can easily be adjusted by changing the spinning speed, even on complex curvilinear surfaces, i.e., a quasi-omnidirectional coating. This excellent film-forming ability without any serious film defects is mainly due to the reduction of line tension among the solution, air, and the substrate at the contact line due to vortex flows of the coating solution on the substrate during the vortex-spin-coating process. As a proof of concept, we present vortex-spin-coated 3D OLEDs fabricated on bi-convex lens substrates which exhibit excellent device performance with high brightness and current efficiency levels comparable to those of a conventional spin-coated 2D planar OLED on a flat substrate. It is also shown that the EL emission from the 3D OLED on the bi-convex lens substrate exhibits a diffusive Lambertian radiation pattern. The results here demonstrate that the vortex-flow-assisted spin-coating process is a promising approach for producing efficient and reliable next-generation OLEDs for 3D conformal opto-electronics.

Dual-Mode, Color-Tunable, Lanthanide-Doped Core–Shell Nanoarchitectures for Anti-Counterfeiting Inks and Latent Fingerprint Recognition

With the rapid development of information in modern society, the research and development of advanced anti-counterfeiting technology is becoming more and more important to protect the security and comprehensiveness of information. Therefore, fluorescent ink as an anti-counterfeiting technology and fingerprint recognition technology as a ″human information identification card″ has attracted the attention of many research groups. Herein, dual-mode (upconversion and downconversion) lanthanide-doped luminescent nanoarchitectures were developed using Y2O3:Er3+,Yb3+ nanoparticles as a core and layered lanthanide hydroxides nanomaterials as a shell. Under the irradiation of 980 nm near-infrared light, the nanoarchitectures emitted a bright upconverted red light emission. Meanwhile, under the irradiation of 254 nm UV light, the nanoarchitectures can directly emit multicolor luminescence (from green to yellow-green, yellow, orange, and red) by changing the suitable ratios of Tb3+/Eu3+ ions. The information can only be extracted when the irradiation of two kinds of excitation light sources existed at the same time, which can improve the difficulty of illegal imitation and enhance the level of anti-counterfeiting. Furthermore, these luminescent nanoarchitectures were investigated for visual latent fingerprint recognition on various substrates with high definition, high sensitivity, and high anti-interference. These results indicated that the nanoarchitectures reported in this study may have great application prospects in information security and identity recognition.

Synthesis, crystal growth, optical, thermal, mechanical and dielectric properties of mono(bis(2-(4-butylphenyl)imino)methyl)phenoxy)zinc(II)dichloride (MBPMP) single crystal as a nonlinear optical (NLO) material

A new mono(bis(2-(4-butylphenyl)imino)methyl)phenoxy)zinc(II)dichloride (MBPMP) single crystal was grown by slow evaporation technique in ethanol. Single crystal XRD studies confirm that the MBPMP crystal is mononuclear, with tetragonal coordination geometry and P41212 noncentrosymmetric space group. The FT-IR spectral analysis was used for identifying the functional groups and bonding nature present in the MBPMP crystal. The UV–Visible-NIR studies reveals that the MBPMP single crystal exhibits a very broad transparency window in the near infrared and visible regions between 220 to 1200 nm and the optical transparency of the MBPMP crystal is 99.49% with the lower cut-off wavelength of 220 nm. The optical energy band gap evaluated from the transmission spectrum was found to be 5.63 eV. The Vickers microhardness number [1.8544 P/d2 kg/mm3] and the work hardening coefficient number (n = 2.326) indicates that the MBPMP single crystal is soft natured. TGA/DSC analysis of the title coordination compound indicated that there is no weight loss up to 209 °C indicating that the grown MBPMP crystal is thermally stable up to 209 °C. MBPMP single crystal exhibits lower dielectric constant and lower dielectric loss at higher frequencies indicating good quality optical crystal. The second harmonic generation efficiency of the MBPMP crystal by using Kurtz’s powder technique employing Q-switched Nd: YAG laser found that the intensity of bright green light emission is 1.2 times greater than that of standard KDP crystal. The laser damage threshold value of the MBPMP single crystal was calculated to be 3.86 GW/cm2.

Single-Step Synthesis of Dual Phase Bright Blue-Green Emitting Lead Halide Perovskite Nanocrystal Thin Films

Metal trihalide perovskites are rapidly redefining the landscape of solid-state semiconductors utilized as active medium in photovoltaics and in light generation. Within this materials space, organic-inorganic hybrid formamidinium lead bromide (FAPbBr3) has arisen as a promising candidate for efferent light emitting devices, due to its capacity for sharp and bright green light emissions (530 nm). Herein we have applied a facile single-step ligand-mediated method for phase-controlled synthesis of FAPbBr3 cube- and rod-shaped nanocrystals (NCs), starting from different ratios of precur-sor agents. Examining their structural and optoelectronic properties – using a combination of synchrotron X-ray diffrac-tion, X-ray spectroscopy, scanning electron microscopy and steady-state and time-resolved photoluminescence (PL) – we reveal the two NC types to fundamentally differ. While the cube-shaped NCs exhibit properties aligning with that of bulk FAPbBr3, the nanorods exhibit a two-phase microstructure and the co-ex...

Optical and spatial resolved cathodoluminescence study of phase separation in green InGaN sandwiched structure grown on GaN nanorods by MOCVD

High indium content InGaN sandwiched structure with bright green light emission was grown on GaN nanorods by MOCVD. The main emission peak is found at ˜580 nm when photoluminescence (PL) measurement was conducted at 300 K. A very stable emission energy at about 2.155 eV was found in temperature-dependent PL with a temperature range from 110 K to 275 K, which may be attributed to the strong localization of carriers in phase-separated InGaN structures. Spatial-resolved cathodoluminescence measurements were conducted to resolve the indium distributions in InGaN layer. A clear evolution of indium phase separation is found, which attributes the high emission efficiency of green InGaN sandwiched structure.

Assembly-Induced Bright-Light Emission from Solution-Processed Platinum(II) Inorganic Polymers

Synthesis, processing, and characterization are reported for a series of tetracyanoplatinate Magnus’ salt (TCN-MS) derivatives—soluble derivatives of the generally intractable Magnus’ green salt—th...

Light-Emitting Electrochemical Cells of Single Crystal Hybrid Halide Perovskite with Vertically Aligned Carbon Nanotubes Contacts

Based on the reported ion migration under electric field in hybrid lead halide perovskites we have developed a bright, light emitting electrochemical cell with CH3NH3PbBr3 single crystals directly grown on vertically aligned carbon nanotube (VACNT) forests as contact electrodes. Under the applied electric field, charged ions in the crystal drift and accumulate in the vicinity of the electrodes, resulting in an in operando formed p-i-n heterojunction. The decreased interface energy barrier and the strong charge injection due to the CNT tip enhanced electric field, result in a bright green light emission up to 1800 cd/m2 at room temperature (average = 60 cd/m2). Beyond the light emission, this original device architecture points to the possibility of implementing vertically aligned CNTs as electrodes in operationally-stable perovskite-based optoelectronic devices.

Nano-aggregates of furan-2-carbohydrazide derivatives displaying enhanced emission with a bathochromic shift.

The non-fluorescent Schiff base compound C1 (N'-((4′-ethyl-3-hydroxy-[1,1′-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) in organic solvent (e.g., THF) was found to produce yellow-green fluorescence emission upon addition of H2O, and granular-shaped aggregates in a THF/H2O mixed solution formed and exhibited obvious aggregation-induced emission (AIE). Especially its keto fluorescence band intensified dramatically, while the enol emission band remained almost unchanged. Hence, a change in fluorescence from no emission of light to emission of bright yellow-green light under a UV lamp was observed with the naked eye. In contrast, the reference compound C2 (N'-((4′-ethyl-3-methoxy-[1,1′-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) showed no intensified fluorescence emission under the same experimental conditions. These results indicated the significant role played by intramolecular H-bonding in the formation of the C1 aggregates and the AIE process.

Self-enzyme chemiluminescence immunoassay capable of rapidly diagnosing the infection of influenza A (H1N1) virus

A highly sensitive self-enzyme immunoassay with 1,1′-oxalyldiimidazole chemiluminescence (ODI-CL) detection was developed for the first time to quantify influenza A (H1N1) virus. A specific capture antibody, capable of capturing hemagglutinin (HA) subtypes of H1N1, was immobilized on the surface of the magnetic Au-Fe3O4 nanocomposite. Neuraminidase (NA) subtype of H1N1 was acts as an enzyme in the self-enzyme immunoassay. A sample mixed with HA antibodies immobilized on the surface of magnetic Au-Fe3O4 nanocomposites was incubated for 1 h at 37 °C. After the incubation, magnetic Au-Fe3O4 nanocomposites separated with a magnetic bar were washed 3 times using phosphate buffered saline with Tween-20 (PBST). Then, 4-Methylumbelliferyl-N-acetyl-α-D-neuraminic acid (MUNANA), a fluorogenic substrate of NA, was added and incubated for 10 min to produce 4-Methylumbelliferone (4-MU) from the enzyme reaction between MUNANA and NA of H1N1. After the incubation, the solution containing 4-MU emitted bright light with the addition of ODI-CL reagents (e.g., H2O2 and ODI). The relative CL intensity of 4-MU was proportionally enhanced with the increase of H1N1. Also, the brightness and color of 4-MU light emitted from the self-enzyme immunoassay was dependent on pH. The self-enzyme immunoassay was able to analyze trace levels of influenza A (H1N1) virus with good accuracy, precision, reproducibility and excellent selectivity. The limit of detection (LOD = 3σ/slope) was as low as 0.19 U/ml. We expect that the self-enzyme immunoassay can be applied as a cost-effective and rapid method capable of selectively quantifying a specific influenza A virus such as H1N1, H3N2, and H5N1.

Efficient Room-Temperature Phosphorescence from Organic-Inorganic Hybrid Perovskites by Molecular Engineering.

Solution-processed organic-inorganic hybrid perovskites are promising emitters for next-generation optoelectronic devices. Multiple-colored, bright light emission is achieved by tuning their composition and structures. However, there is very little research on exploring optically active organic cations for hybrid perovskites. Here, unique room-temperature phosphorescence from hybrid perovskites is reported by employing novel organic cations. Efficient room-temperature phosphorescence is activated by designing a mixed-cation perovskite system to suppress nonradiative recombination. Multiple-colored phosphorescence is achieved by molecular design. Moreover, the emission lifetime can be tuned by varying the perovskite composition to achieve persistent luminescence. Efficient room-temperature phosphorescence is demonstrated in hybrid perovskites that originates from the triplet states of the organic cations, opening a new dimension to the further development of perovskite emitters with novel functional organic cations for versatile display applications.