Light Emission Characteristics Research Articles

Improving the performance of quantum well solar cells with photonic crystal.

The fabrication of quantum well solar cells with surface photonic crystal (SPC) and embedded photonic crystal (EPC) structures has resulted in solar cells with improved properties. When compared to reference solar cells (RSCs), the photoluminescence (PL) intensities of SPC solar cells and EPC solar cells have been enhanced by 89% and 114%, respectively. This indicates improved light absorption and emission characteristics in the presence of the periodic patterns (PCs). The short-circuit current (Isc) of EPC solar cells is 31% higher than that of RSCs, suggesting improved light absorption and carrier generation. On the other hand, SPC solar cells exhibit a 6% higher Isc compared to RSCs, and the open-circuit voltage has increased simultaneously. The fill factors (FF) of the solar cells are 84% for RSCs, 86% for SPC solar cells, and 76% for EPC solar cells. The higher FF in SPC solar cells suggests improved charge carrier collection efficiency. In terms of photoelectric conversion efficiency, SPC solar cells demonstrate a 10.6% increase, while EPC solar cells show a 7.7% increase. These improvements indicate that the incorporation of PCs in the solar cells enhances their ability to convert light into electrical energy. These findings highlight the potential of photonic crystals engineering for enhancing the performance of solar cells.

Optical properties of Gd3+ doped bismuth silicate crystals based on first principles

Bismuth silicate (Bi4Si3O12, BSO) crystal, as a nonlinear optical material with excellent optical properties, has a wide range of applications in laser technology, optical communication, and optical information processing. In order to further improve its performance, this study adopts a first principles calculation method based on density functional theory (DFT), selects Gd3+ as the dopant, and calculates and explores the changes in optical properties of BSO crystals after doping with 1/12, 1/6, and 1/3Gd3+. The calculation results show that the doping of Gd3+ changes the electronic structure of BSO crystals, which is manifested in the emergence of new light absorption and emission characteristics, an increase in carrier concentration, an improvement in conductivity, and an enhancement of crystal polarization ability in optical properties. In addition, doping with Gd3+ increases the light transmission rate and reduces energy loss of BSO crystals, while releasing more energy during electron band transitions, effectively improving the luminescence performance of BSO crystals. The theoretical research in this article provides an important theoretical basis for understanding the influence of Gd3+ doping on the optical properties of BSO, and by optimizing the ratio of Gd3+, the optical properties of BSO can be further regulated, opening up new possibilities for its application in optoelectronic devices.

Tunable GaAsxP1-x Quantum-Dot Emission in Wurtzite GaP Nanowires.

We present a fairly understudied material system suitable for the realization of tunable quantum-dot (QD) emission within the visible-to-near-infrared spectrum (in particular, in the 650-720 nm wavelength range). Specifically, crystal-pure wurtzite gallium phosphide (GaP) nanowires (NWs) are synthesized, incorporating single gallium arsenide phosphide (GaAsxP1-x) QDs of various compositions. Detailed growth procedures are outlined, accompanied by an analysis of the synthesis challenges encountered during the realization of these nanostructures and the strategies to solve them. Notably, a great degree of control over the shape and composition of the ternary alloy QD is achieved, enabling a well-defined confinement and the tunability of the emission wavelength. This is confirmed by low-temperature microphotoluminescence (μ-PL) investigation showing that the NW emission is dominated by a narrow peak whose energy shifts according to the As content of the QD: from ∼650 nm (As = 70%) to ∼720 nm (As = 90%). Moreover, a localized and efficient carrier recombination mechanism is found by single-NW μ-PL mapping, confirming that this emission arises from the QD. Finally, a power and temperature μ-PL study is presented and used to characterize the QD excitonic properties and the nature of the involved energy levels. Our findings underscore the potential for these QDs in NWs with tailored compositions to achieve the desired light emission characteristics, thereby advancing applications in quantum optics and nanophotonics.

Event-based high-resolution neutron image formation analysis using intensified CMOS cameras

We present a versatile optical setup for high-resolution neutron imaging with an adaptable field of view and magnification that can resolve individual neutron absorption events with an image intensifier and a CMOS camera. Its imaging performance is characterized by evaluating the resolution limits of the individual optical components and resulting design aspects are discussed. Neutron radiography measurements of a Siemens star pattern were performed in event mode acquisition comparing two common high-resolution neutron scintillators, crystalline Gadolinium Gallium Garnet (GGG) and powdered Gadolinium Oxysulfide (GOS). An analysis of the light signature caused by neutron absorption events is performed and some resulting issues for both GGG and GOS regarding optical system design are addressed. Both scintillators reach similar resolution (4–5 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upmu }$$\\end{document}m) in event mode acquisition despite different light emission characteristics. The findings suggest that, in the case of GOS, the resolution is limited by the size of the light clusters which in turn originate from the photon scattering at the boundaries of the powder particles comprising it, while with GGG the lower light conversion efficiency makes it challenging to collect enough photons to trigger sufficient signal amplification in the image intensifier. Overall, the proposed event-based evaluation of scintillators allows for quantifying and optimizing various design parameters, which is much more complex than adopting conventional methods based on integrated images.

Warm-White Light Emission of Lead-free CsAg2I3 Single Crystal Scintillator with a One-Dimensional Electronic Structure.

Presently, the exploration of novel inorganic lead-free perovskite scintillators has emerged as a prominent topic in the field of perovskite materials. Extensive attention has been garnered by materials such as Cs3Cu2I5 due to their notable advantage in scintillation intensity, but the response time constants in the microsecond or even millisecond range severely constrain their potential applications in scintillators. In this study, large-sized (5-6 mm) CsAg2I3 single crystals with an ultrafast warm-white light emission on a nanosecond time scale are presented. Specifically, upon X-ray excitation, the single crystal demonstrates a broad-spectrum white light emission with a color temperature as high as 5129 K, attributed to its self-trapped exciton emission. The 137Cs energy spectrum reveals that CsAg2I3 possesses an ultrafast response for γ rays with a time constant of 15 ns, which is significantly faster than that of Cs3Cu2I5. Furthermore, time-resolved photoluminescence unveils a subnanosecond component with a response time of 0.9 ns. The characteristics of ultrafast warm-white light emission exhibit the significant potential of CsAg2I3 in radiation scintillation detection and its probability of playing a pivotal role in future radiation detection technology.

Characteristics of light emission and wear behaviour of a reinforced composite material made of basalt and jute for optimum parameters

Characteristics of light emission and wear behaviour of a reinforced composite material made of basalt and jute for optimum parameters

White light emission in Bi3+/Te4+ co‐doped Cs2SnCl6 for adjustable daily lighting and visible light communication

Abstractns2 ions‐doped lead‐free perovskites have garnered significant attention for their potential in diverse optoelectronic applications, owing to their broad emission characteristics arising from self‐trapped excitons (STEs). Herein, high‐performance white light‐emitting diodes (WLEDs) for intelligent lighting are developed by Bi3+/Te4+co‐doped Cs2SnCl6. Effective energy transfer between the dual STE emissions results in tunable broadband emissions covering the full‐color region. Adjustable WLEDs containing cold‐ and warm‐white lighting are fabricated. The WLEDs have excellent luminescent performances coupled with adjustable correlated color temperatures of 6417 and 3829 K. This versatility allows them to meet lighting demand for different scenarios, which is essential for future WLEDs to achieve healthy lighting. In addition, the excellent white light emission characteristics can also be applied in the visible light communication (VLC) system, achieving a −3 dB bandwidth of 13.3 MHz and opening eye diagrams in the data rate range of 10–60 Mbps. This work represents a significant advancement toward building intelligent health lighting applications and achieving high‐quality light sources for VLC based on lead‐free perovskites.

Perylene-3,4,9,10-tetracarboxylic dianhydride dye intercalated liquid crystal molecules: Synthesis, spectroscopic characterizations and photoluminescence dynamics

The present research explores the interaction between perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)-dye (PD) and 3b {(E)-1-[3-fluoro-4-(pentyloxy)phenyl]-2-(4-methylphenyl)diazene} liquid crystal (LC) mesophase, 3c{(E)-1-[3-fluoro-4-(hexyloxy)phenyl]-2-(4-methylphenyl)diazene} nematic liquid crystal (NLC) molecule. Spectroscopic characterizations of 3b@PD LC mesophase and 3c@PD NLC molecule were carried out using scanning electron microscopy (SEM), polarizing optical microscope (POM), Raman, Fourier transform infrared spectroscopy (FT-IR), and UV–visible analytical methods. The UV–visible studies revealed a red shift in absorption bands (348.0 nm to 374 nm) with a decrease in optical band gap from 2.43 eV to 2.25 eV. Room temperature photoluminescence (RTPL) spectra of 3b@PD LC mesophase exhibited blue light emission characteristics centred at 453.1 nm and 3c @PD NLC molecule showed broad emission peaks located at 400.7 nm and 324.8 nm. Steady-state photoluminescence (SSPL) spectra showcased indigo-purple emission bands corresponding to the wavelengths 303–353 nm, 420.5 nm, 418 nm, 418.3 nm, and 347.0 nm, however, for the 3c@PD NLC molecule, emission intensity peaks appeared at 429.6 nm, 418.0 nm and 329.0 nm. The stoke’s shift for 3b@PD LC mesophase varied between 0.01 eV to 0.613 eV while for 3c@PD NLC molecule it was found in between 0.317 eV to 0.453 eV. POM analysis unveiled distinct fan-like textures with varied colour interfaces. Time-resolved photoluminescence (TRPL) decay studies unveiled average lifetime of 3b@PD LC mesophase was 1.80 ns, 0.98 ns, 0.308 ns and for 3c@PD NLC molecule, the average lifetime was found to be 0.98 ns, 0.82 ns, and 0.306 ns at various excitation wavelengths. However, phosphorescence decay studies showed faster decay characteristics for 3c@PD NLC molecule (1.40 ns to 4.00 ns) compared with 3b@PD LC mesophase (1.65 to 5.42 ns) when excited at various wavelengths. The interaction between LC molecules and PTCDA demonstrated a significant enhancement in RTPL, TRPL, and SSPL properties, suggesting promising applications in photonics and optoelectronics.

Damage Characteristics Analysis of Laser Ablation Triple-Junction Solar Cells Based on Electroluminescence Characteristics.

To study the physical property effects of the laser on GaInP/GaAs/Ge solar cells and their sub-cell layers, a pulsed laser with a wavelength of 532 nm was used to irradiate the solar cells under various energy conditions. The working performance of the cell was measured with a source meter. The electroluminescence (EL) characteristics were assessed using an ordinary and an infrared camera. Based on the detailed balance theory, in the voltage characteristics of an ideal pristine cell, the GaInP layer made the most significant voltage contribution, followed by the GaAs layer, with the Ge layer contributing the least. When a bias voltage was applied to the pristine cell, the top GaInP cell emitted red light at 670 nm, the middle GaAs cell emitted near-infrared light at 926 nm, and the bottom Ge cell emitted infrared light at 1852 nm. In the experiment, the 532 nm laser wavelength within the response spectrum bands of the GaInP layer and the laser passed through the glass cover slip and directly interacted with the GaInP layer. The experimental results indicated that the GaInP layer first exhibited different degrees of damage under laser irradiation, and the cell voltage was substantially attenuated. The GaInP/GaAs/Ge solar cell showed a decrease in electrical and light emission characteristics. As the laser energy increased, the cell's damage intensified, gradually leading to a loss of photoelectric conversion capability, the near-complete disappearance of red light emission, and a gradual degradation of near-infrared emission properties. The EL imaging revealed varying damage states across the triple-junction gallium arsenide solar cell's sub-cells.

Terbium-benzoyl acetate complex encored indium-MOFs through post-synthetic modification for luminescent sensitive detection of organophosphorus insecticides

Metal-organic frameworks (MOFs) are represented ideal candidate materials for chemical sensing of different kinds of species because they contain optically active sites may be in organic linker or ions node, moreover, MOFs have high porosity that capture different types of guests. Lanthanide MOFs (Ln-MOFs) was very common in sensing chemical species due to identical light emission characteristics. The problem of Ln-MOFs was the difficulty of its preparation; therefore, post-synthetic modification (PSM) technique was excellent for incorporation of lanthanide site in the network. Unlike other MOFs, In-MOF can be post-synthesized because of its free amino group in the network, therefore, it was chosen in the current work. Here, Tb-In-MOF-EBA was generated by PSM of In-MOF in two steps: (1) formation of the amide by the reaction of In-MOF with ethyl benzoyl acetate; (2) chelation of Tb3+ cations by the diketone fragment. The main challenge of present work is not to give another luminescent MOF based sensor rather than using decorative technique based PSM route to tune optically active sensors for organophosphorus (OP) insecticides (dimethoate, chlorpyrifos, and pirimiphos-methyl) identification quantitatively and qualitatively. The emission intensity of Tb-In-MOF-EBA were reduced with 8 %, 50 %, and 81 %, after adding dimethoate, chlorpyrifos, and pirimiphos-methyl for the parent compounds, respectively. Tb-In-MOF-EBA showed interesting selectivity toward dimethoate, chlorpyrifos, pirimiphos-methyl, therefore, it can be used in measuring the concentration of OP insecticide with high accuracy.

Symmetry breaking of bound states in the continuum in luminescence response of photonic crystal slabs with embedded Ge nanoislands

Bound states in the continuum (BIC) have attracted a great deal of attention in all-dielectric nanophotonics due to their ability to provide spectral features with a very high-quality factor. By definition, BIC cannot be observed in the far field because of the symmetry mismatch with the modes propagating in free space. Despite this, in systems with slightly reduced symmetry, the condition for BIC is lifted, which gives rise to the high-quality resonant features in their optical response. In particular, in photonic crystal slabs, which support the BIC states, the symmetry reduction allows modification of light propagation, reflection, or emission. In this work, using the photonic crystal slabs with embedded Ge nanoislands, we have shown the ability to control their light emission features by symmetry breaking. It was demonstrated that such symmetry breaking due to a change in the basis vectors of the photonic crystal unit cell or a change in the unit cell internal structure could provide independent control knobs to alter the spectral position of photonic crystal modes, their dispersion, and degeneracy. The obtained results reveal additional ways to manage the light emission of active media in photonic crystal slabs.

Evaluation of shielding performance and light emission characteristics of luminescent radiation shields using Gd2O2S

ABSTRACT Gadolinium oxysulfide (Gd2O2S: GOS) has a large absorption cross-section for thermal neutrons and a mass density similar to that of iron used for shielding against X and γ-ray radiation. During GOS scintillator production process, its waste is also generated. If GOS waste can be used as an effective shielding material, it is worthwhile as beneficial use of the waste. We developed a novel radiation-shielding material using GOS waste. The developed shielding material can shield X, γ-rays and thermal neutrons more efficiently than conventional shielding materials and emit visible light due to leaked radiation when the shielding material is damaged, which subsequently be used to check the integrity of shielding using visible light. In this study, two types of shields, concrete and mortar with GOS as the aggregate and epoxy resin with GOS were prototyped and tested for radiation transmission. Results indicate that GOS shielding has a 10% higher shielding ability for X and γ-rays than heavy concrete with iron as aggregate. Additionally, the same shielding effect for thermal neutrons was attained at 1/10 the thickness of heavy concrete. Thus, using GOS waste is not only cost effective but also contributes to a circular economy.

Light Emission Characteristics in Nitride Semiconductor Nanowires Fabricated by Top‐down Method

Nanophotonic devices made from nitride semiconductors are promising for various applications, especially those utilizing ultraviolet‐visible light with low‐power consumption and high driving speed. Herein, nanowire structures are fabricated from a light‐emitting diode epitaxial wafer and demonstrates the effectiveness of wet etching in top‐down fabrication. Spontaneous emission from active layers and unanticipated lasing derived from a GaN layer in a single nanowire are observed by microphotoluminescence measurement. Lastly, the lasing mode through a 3D simulation of the eigenmodes in this nanowire structure is clarified.

Chemiluminescent wood

Wood materials incorporating new properties are of great interest, especially for advanced applications such as sustainable optics and photonics. In this work we describe a wood functionalization approach, comprising the incorporation of artificial chemiluminescent systems (phenyl oxalate ester‑hydrogen peroxide-fluorophore, and luminol-ferricyanide), resulting in light-emitting wood. By a detailed characterisation of the light emission features we point out the complex interaction between wood scaffold and chemiluminescent systems, especially the quenching effect of wood extractives (for the TCPO-H2O2-fluorophore system) and lignin (for the luminol-ferricyanide system). Moreover, we take advantage of the intrinsic anisotropic porosity and capillarity of wood tissue to study the chemiluminescent front propagation. Our results may inspire the development of novel light-emitting wood materials for a variety of applications, from fundamental studies of water uptake in wood to sensors and even design elements.

Intriguing Role of Weak Electron Donor in Dictating the Luminescent Characteristics of DS‐A‐DW Materials

AbstractThe short wavelength (SW) emission region of the materials employing strong donor (DS) phenothiazine (PTZ) is generally correlated to its quasi‐axial (QAPTZ) conformer arrangement. This propels to investigate the specific role of weak donors (DW) such as carbazole (CZ) in determining the emission characteristics of molecular heredity (MH) type structural design encompassing dual donors of varying strength. For this purpose, a common DS(PTZ)–Acceptor unit is linked to the DW(CZ) unit via different linkage positions to form M1, M2, and M3, which not only alters the absorption and dual emission characteristics but also influences the delayed fluorescence phenomenon. The SW emission originates by minimizing the aggregation factor rather than by literature envisaged QAPTZ conformer. Incorporating M1 as a single molecular white light emitter (SMWLE) in near UV light emitting diode (LED) devices results in cold white light emission with CRI of 68 and CIE of (0.24, 0.33), while its corresponding solution‐processed organic light‐emitting diode devices delivers warm white electroluminescence with an EQE of 5.8%. Overall, this work demonstrates the significant contribution of the DW in attaining the white light emission characteristics of MH molecular design not only at the molecular level but also in practical light‐emitting devices.

Ultra-broadband triple-peak white light-emitting carbonized polymer dots materials based on Förster resonance energy transfer

Carbonized polymer dots (CPDs) with white-light-emitting property have greatly promising application in next generation of lighting and display technologies. However, most of the reported CPD materials exhibit single peak emission and narrow emission band, resulting in difficulty to obtain white-light emission. In this work, the ultra-broadband triple-peak emission (red, green, and blue) CD-based materials with high-efficiency white light-emitting property are realized for the first time by the Förster resonance energy transfer (FRET). Blue and green emissions are derived from the fluorescence and phosphorescence of donor CPDs, while the red light is derived from receptor by FRET. Remarkably, the fabricated CPD materials show bright pure white-light emission with high overall quantum yield (QY) of 36% and the full width at half maximum of 235 nm. Besides, afterglow colors of CPD-based materials can be tuned from green to red by adjusting the ratio of donor and acceptor. Based on the high-efficiency and wide-spectrum pure white light emission characteristics of CPD-based composites, white light emitting diodes were fabricated and they exhibit bright warm white light with CIE and CCT of (0.35, 0.31) and 4041 K.

Enhancement of light emission characteristic of a GaAs-based Gunn light emitting diode with a quasi-cavity

Enhancement of light emission characteristic of a GaAs-based Gunn light emitting diode with a quasi-cavity

Exploring CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals in Amorphous Oxide Glasses: Innovations in Fabrication and Applications.

Metal halide perovskites with excellent optical and electronic properties have become a trending material in the current research. However, their limited stability under ambient conditions degrades quality and threatens their potential commercialization as optoelectronic devices. Various approaches are adopted to improve the stability of perovskite nanocrystals (PeNC) while maintaining their advantageous optical properties, particularly strong luminescence. Among different possible improvement strategies, encapsulation of PeNCs within the amorphous glass matrices of inorganic oxides has drawn widespread attention because it ensures high resistance against chemical corrosion and high temperature, thus enhancing their chemical, thermal, and mechanical stability with improved light-emission characteristics. In this article, two types of materials, namely all-inorganic metal halide PeNCs and amorphous oxide glasses are briefly introduced, and then the methods are reviewed to fabricate and improve the quality of PeNC@glass composites. These methods are classified into three universal categories: compositional modification, structural modification, and dual encapsulation. In the final part of this review paper, examples of applications of PeNCs@glass composites in light-emitting devices and displays, data storage and anti-counterfeiting, lasing, photodetectors and X-ray detectors, photocatalysis, optical filters, solar concentrators, and batteries are provided.

Effect of a retrofitted metallic microfiber partial flow diesel particulate filter on a light duty diesel vehicle particle emission characteristics

This study was conducted two distinct experiments, using a light-duty diesel vehicle at various engine speeds and loads as well as the new European driving cycle (NEDC) comparing commercial diesel fuel (B7) and pure biodiesel (B100). The NEDC involves a combination of urban and extra urban driving conditions. It aims to study a diesel vehicle's thermal efficiency as well as its gaseous and particulate matter (PM) emissions. This involves comparing results with and with no diesel oxidative catalyst (DOC) and a partial flow diesel particulate filter (PDPF) system. The surface morphology, micro- and nanostructure of a diesel vehicle's PM were also examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to determine nanostructural and dimensional changes after mounting a DOC-PDPF system. Comparison of B7 and B100 combustion showed that B100 had around 1 % increase in brake thermal efficiency (BTE) at 1500 and 2000 rpm compared to B7 since B100 is a more oxygenated biofuel. At 2500 rpm, similar BTE values were observed. Introduction of a DOC-PDPF system resulted in an approximately 1 % BTE reduction for both fuels. This was due to greater friction losses caused by backpressure from the DOC-PDPF system. Increased exhaust backpressure was progressive, ranging from 1 kPa at idle speed to 6 kPa at high engine speeds for both tested fuels. The DOC-PDPF system respectively minimized PM emissions and particle numbers (PNs) by more than 50 % and 35 % for B7 and 71 % and 31 % for B100. These results are average values under the various phases of NEDC testing. A 30 % decrease in PM and a 44 % reduction in PNs under the overall test cycle were found when B100 was tested compared to B7. The soot primary particle size was reduced from 34.69 to 29.08 nm and the carbon fringe length diminished from 1.25 to 0.949 nm at different pre- and post-DOC-PDPF locations. This was due to partial oxidation on the surfaces of the PDPF metallic microstructure. PM undergoes simultaneous partial oxidation after passing through the DOC-PDPF system, as confirmed by TGA analysis.

Superior white electroluminescent devices using nitrogen-doped carbon dots/TiO2 nanorods heterostructures

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390–900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d’Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications.