Application In Light-emitting Diodes Research Articles

Tetravalent manganese-doped lithium meta-silicate red-emitting phosphors for LED applications: structural and luminescence properties

In this paper, different concentrations of tetravalent manganese-activated lithium meta-silicate red-emitting phosphors, namely Li2SiO3:xMn4+ (x = 0.01, 0.02, 0.03, 0.04 and 0.05 mol), have been prepared by the solid-state reaction method at 950 °C. The structural, thermal, morphological, and optical properties of the sintered phosphors were characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), raman, UV-Visible and photoluminescence (PL) spectra. Excitation and emission spectra are used to study optical characteristics, which match well with the commercially visible region. The red emission bands for Li2SiO3:0.02Mn4+ peak at approximately 642 nm (λex = 425 nm) and 717 nm (λex = 475 nm), respectively due to the spin-forbidden 2E → 4A2 transition. The doping concentrations of xMn4+ in the Li2SiO3 host were investigated, and the correlations between Mn4+ doping concentration and luminescence intensity were examined. The Commission Internationale de l'Eclairage (CIE) chromatic coordinate graph confirmed the emission color observation in the red region, showed an excellent color purity (CP). In addition, the quantum efficiency (QE) of Li2SiO3:Mn4+ phosphors reached up to 70.51%. The investigation shows that synthesized Li2SiO3:Mn4+ phosphors are beneficial for red Light-Emitting Diodes (LEDs) used in solid-state lighting.

The Effective Parameters on the Performance of Finned Heat Sinks Used for Light Emitting Diode Application: A Review

The increasing demand for high-performance LED applications has led to the development of thermal management systems to reduce heat generation. This review paper examines finned heat sinks for LED applications, examining the impact of fin number, height, thickness, shape, type, direction, and materials used. The study concludes that creating holes in the fins improves heat sink performance, while shape, size, and number also affect heat transfer rate and temperature drop along the fins. This research highlights the importance of efficient thermal management systems in LED applications. This review paper examines the impact of various parameters on the performance of finned heat sinks used for LED applications. It explores the influence of fin number, height, thickness, shape, type, direction, and materials on heat transfer rate and temperature drop along the fins. The study emphasizes the importance of efficient thermal management systems in LED applications. From the beginning of March until the end of August 2022, tests will be conducted to determine the sensitivity of single-glass solar modules to environmental changes.

Highly luminescent and stable CsPbBr3 perovskite nanocrystals coated with polyethersulfone for white light-emitting diode applications.

Simultaneously improving the stability and photoluminescence quantum yield (PLQY) of all inorganic perovskite nanocrystals (NCs) is crucial for their practical utilization in various optoelectronic devices. Here, CsPbBr3 NCs coated with polyethersulfone (PES) were prepared via an in-situ co-precipitation method. The sulfone groups in PES bind to undercoordinated lead ion (Pb2+) on the CsPbBr3 NCs, resulting in significant reduction of surface defects, thus enhancing the PLQY from 74.2% to 88.3%. Meanwhile, the PES-coated NCs exhibit high water resistance and excellent heat and light stability, maintaining over 85% of the initial PL intensity under thermal aging (70°C, 4h) and continuous 365 nm ultraviolet (UV) light irradiation (24 W, 8h) conditions. By contrast, the PL intensity of the control NCs dramatically dropped to less than 40%. Finally, a diode emitting bright white light was fabricated utilizing the PES-coated CsPbBr3 NCs, which exhibits a color gamut of ~110% NTSC standard.

Optical property dataset of inorganic phosphor

Developing inorganic phosphor with desired properties for light-emitting diode application has traditionally relied on time-consuming and labor-intensive material development processes. Moreover, the results of material development research depend significantly on individual researchers’ intuition and experience. Thus, to improve the efficiency and reliability of materials discovery, machine learning has been widely applied to various materials science applications in recent years. However, the prediction capabilities of machine learning methods fundamentally depend on the quality of the training datasets. In this work, we constructed a high-quality and reliable dataset that contains experimentally validated inorganic phosphors and their optical properties, sourced from the literature on inorganic phosphors. Our dataset includes 3952 combinations of 21 dopant elements in 2238 host materials from 553 articles. The dataset provides material information, optical properties, measurement conditions for inorganic phosphors, and meta-information. Among the preliminary machine learning results, the essential properties of inorganic phosphors, such as maximum Photoluminescence (PL) emission wavelength and PL decay time, show overall satisfactory prediction performance with coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^2$$\\end{document}) scores of 0.7 or more. We also confirmed that the measurement conditions significantly improved prediction performance.

Tunable electronic and optical properties of BAs/WTe2 heterostructure for theoretical photoelectric device design

The geometric structure of the BAs/WTe2 heterojunction was scrutinized by employing ab initio calculations grounded on density functional theory. Multiple configurations are constructed to determine the equilibrium state of the heterojunction with optimal stability. The results show that the H1-type heterojunction with interlayer distance of 3.92 Å exhibits exceptional stability and showcases a conventional Type-II band alignment, accompanied by a direct band gap measuring 0.33 eV. By applying external electric field and introducing strain, one can efficaciously modulate both the band gap and the quantity of charge transfer in the heterojunction, accompanied by the transition of band alignment from Type-II to Type-I, which makes it expected to achieve broader applications in light-emitting diodes, laser detectors and other fields. Ultimately, the heterojunction undergoes a transformation from a semiconducting to a metallic state. Furthermore, the outstanding optical characteristics inherent to each of the two monolayers are preserved, the BAs/WTe2 heterojunction also serves to enhance the absorption coefficient and spectral range of the material, particularly within the ultraviolet spectrum. It merits emphasis that the optical properties of the BAs/WTe2 heterojunction are capable of modification through the imposition of external electric fields and mechanical strains, which will expand its applicability and potential for future progression within the domains of nanodevices and optoelectronic apparatus.

Suppressing nonradiative recombination enables highly efficient red perovskite light-emitting diodes

Quasi-two-dimensional perovskites are promising emitters for red light-emitting diodes. However, the practical application of red perovskite light-emitting diodes (PeLEDs) is still limited by the defect-induced nonradiative recombination. In this study, we demonstrate efficient red PeLEDs by introducing the diethylene glycol bis(3-aminopropyl) ether (DGBE) additive. The coupling effect between oxygen (O) atoms in DGBE and unsaturated Pb2+ not only regulates crystallization, but also passivates defects. Benefiting from the reduced defect densities and enhanced radiative recombination efficiencies, the photoluminescence quantum yield (PLQY) increases from 39 % to 80 %. Consequently, we achieve high-performance red PeLEDs with a maximum external quantum efficiency of 24.2 %, which provides a reliable approach to promote the development of highly efficient red PeLEDs.

Ultrafast spin-flip exciton conversion and narrowband sky-blue luminescence in a fused polycyclic selenaborin emitter.

Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho[3,2,1-de]anthracene (SeBSe) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet-triplet energy gap (ΔE ST) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in SeBSe by virtue of the heavy-atom effect of selenium atoms. Consequently, SeBSe allows ultrafast spin-flip RISC with the rate constant surpassing 108 s-1, which far exceeds the corresponding fluorescence radiative decay rate (∼106 s-1), enabling an ideal singlet-triplet superimposed excited state.

First-principles study on structural, electronic, and optical properties of mixed alloys of Cs2Ag(SbxBi1−x)Br6 double perovskites for optoelectronic applications

Halide perovskites have attracted promising capabilities of solar cells and light-emitting diode applications due to their high stability and optoelectronics performance. In this work, the effect of chemical substitution on the structural, electronics, and optical properties of mixed alloy Cs2Ag(SbxBi1-x)Br6 perovskites (when x is a mixing ratio varying from 0.0 to 1.0) was explored by using the virtual crystal approximation within the first-principle framework based on DFT-GGA, GGA-TB09, RPA, and BSE. Calculation results reveal that the lattice constant increases linearly as a function of the mixing ratio of a(x) = 11.246–0.0012x Å. These results satisfied the Vegard’s law as well as the reliability of virtual crystal approximation. The band structure calculated with and without the spin–orbit coupling was compared. Band gap of the mixed alloys are lower than that of pure Sb or pure Bi compounds. The band gap increases as a quadratic function of Eg = 2.07 – 0.279x – 0.121x2 eV. The smaller band gap of the mixed alloy results from the energy mismatch between Sb and Bb s and p orbitals. Calculations from DFT-TB09 are in good agreement with experimental results. Blue-shifted absorption spectra to the ultraviolet region were found when the Sb content increased. A linear increase of the static dielectric constant was found when the Sb content increased as a function of εs(x) = 2.849 + 0.266x. BSE@PBEsol calculations are consistent with experimental profiles. Calculation results indicate that the mixed alloy Cs2Ag(SbxBi1-x)Br6 can be tuned regarding its electronic and optical properties.

Extended Conjugation Strategy Enabling Red-Shifted and Efficient Emission of Orange-Red Thermally Activated Delayed Fluorescence Materials.

In account of the energy gap law, the development of efficient narrow-band gap thermally activated delayed fluorescence (TADF) materials remains a major challenge for the application of organic light-emitting diodes (OLEDs). The orange-red TADF materials are commonly designed with either large π-conjugated systems or strong intramolecular donor-acceptor (D-A) interactions for red-shift emission and small singlet-triplet energy gap (ΔEST). There are rare reports on the simultaneous incorporation of these two strategies on the same material systems. Herein, two orange-red emitters named 1P2D-BP and 2P2D-DQ have been designed by extending the conjugation degree of the center acceptor DQ and increasing the number distribution of the peripheral donor PXZ units, respectively. The emission peak of 1P2D-BP is red-shifted to 615 nm compared to 580 nm for 2P2D-DQ, revealing the pronounced effect of the conjugation extension on the emission band gap. In addition, the distorted molecular structure yields a small ΔEST of 0.02 eV, favoring the acquisition of a high exciton utilization through an efficient reverse intersystem crossing process. As a result, orange-red OLEDs with both 1P2D-BP and 2P2D-DQ have achieved an external quantum efficiency (EQE) of more than 17%. In addition, the efficient white OLED based on 1P2D-BP is realized through precise exciton assignment and energy transport modulation, showing an EQE of 23.6% and a color rendering index of 82. The present work provides an important reference for the design of high-efficiency narrow-band gap materials in the field of solid-state lighting.

Enhancing light output of WSLED with microlens array fabricated on Tb³⁺/Sm³⁺ co-doped fluorophosphate glass via hot embossing

In this study, Tb3+/Sm3+ co-doped NaPO3–BaF2–AlF3–CaF2 glasses were synthesized using the melt quenching method. These glasses exhibit a glass transition temperature below 380 °C and maintain optical transparency close to 90% within the visible spectrum. Furthermore, under UV excitation, the emission shows a wide spectrum and varies with the rare-earth doping ratio or excitation wavelength. Hence, this glass was introduced into the wide-spectrum light-emitting diode (WSLED) application. Moreover, a microlens array was fabricated on the glass surface using the hot embossing technique. In fact, the microlens array enhanced the light output power of the WSLED by 5% at a driving current of 150 mA.

One-Step Extrusion Preparation for Low-Cost Multicolored Carbon Dot Fluorescent Films.

Carbon dots (CDs), an emerging class of environmentally friendly luminescent materials, have been extensively applied in full-color display of light-emitting diodes (LEDs). However, the synthesis of CDs usually requires high pressure, and the conventional preparation of CD-based LED films involves intricate manufacturing techniques. The resulting security risk and high cost restrict the further application of CD-based LEDs. Here, we present a cost-effective method to obtain CD-based LED films via in situ extrusion in a twin-screw extruder. By fine-tuning the extrusion temperature, we created blue-emitting LEDs. The resulting fluorescent films exhibited remarkable stability, retaining 94% fluorescence intensity after 180 days of storage. We also prepared yellow, pure white, and cool white LEDs with malleable shapes, validating the versatility of the in situ extrusion method. More importantly, the manufacturing cost for CD-based films amounts to only about 0.8 RMB/g, which is substantially lower than that of the reported preparation methods. This work offers a cost-effective, safe, and massive approach to preparing photoluminescent LEDs, paving the way for the development of more sustainable and efficient CD-based LEDs.

Effect of annealing temperature and doping concentrations on structure and optical properties of Eu3+-doped TiO2 nanomaterials

In this study, we successfully synthesized europium-doped TiO2 (TiO2:Eu3+) nanomaterials (NMs) with crystalline sizes ranging from 6.5 to 71.7 nm through a sol-gel method. Analysis of X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra indicates that the substitution of smaller-sized Ti4+ ions (0.745 Å) by larger-sized Eu3+ ions (0.947 Å) was more efficient at higher doping concentrations and annealing temperatures. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the synthesized TiO2:7%Eu3+NMs exhibit a strong red emission band peaking at 613 nm and remarkable absorption in the blue light region centered at 463 nm, making them suitable for use in white light-emitting diode (WLED) applications. Our findings reveal that both annealing temperature and doping concentration significantly influence the structure and properties of these materials. Besides, the research team has seen, under the experimental conditions, the TiO2:7%Eu3+ sample annealed at 800°C exhibits the highest PL intensity. These results underscore the potential of the synthesized TiO2:Eu3+ NMs as red-emitting materials for WLED applications.

Low-temperature photoluminescence characteristic of Tm-doped Ga2O3 films for light emitting diodes application

Tm-doped Ga2O3 films hold significant promise for application in light-emitting diodes (LEDs). A comprehensive understanding of their photoluminescence properties is pivotal for unlocking their full potential. In this work, we present findings on the photoluminescence (PL) spectra of Tm-doped Ga2O3 films, elucidating variations at different measurement temperatures and excitation energies utilizing synchrotron radiation light. The intensity of ultraviolet light (UVL1 and UVL2) exhibits a temperature dependence and its activation energy illustrates an ionization energy of shallow donor and migration through tunneling of self-trapped holes to triply ionized Ga vacancy (VGa) centers forming doubly ionized VGa acceptors. Additionally, the excitation energy-dependent PL spectra provide insights into the excitation mechanism of Tm ions, indicating a most likely through defects in the Ga2O3 host.

Lead-free Cs₂NaInCl₆:Bi³⁺/Mn2⁺ double perovskite nanocrystals to nanosheets with improved photoluminescence quantum yield for anti-counterfeit marks and LED applications

Lead-free double perovskites (DPs) in the form of two-dimensional (2D) nanosheets (NSs) have emerged as exceptional candidates compared to zero-dimensional (0D) nanocrystals (NCs). This preference is attributed to their intriguing fundamental properties and promising applications in optoelectronics. Notably, NSs offer superior performance due to their enhanced surface passivation capabilities, facilitating more efficient treatment of surface defects and thereby enhancing optoelectronic properties. However, the realization of Cs2NaInCl6 as lead-free DPs NSs is yet to be achieved. In this study, we successfully synthesized Cs2NaInCl6 co-doped with Bi3+/Mn2+ NSs. The two-step solution process synthesis enables us to achieve dimensionality control, progressing from 0D NCs to 2D NSs. Comprehensive optical spectroscopy analyses reveal that the NSs exhibit a suppressed non-radiative decay rate (Knr) of 5.03 × 10−3 ns−1 in contrast to NCs with a Knr of 3.21 × 10−2 ns−1. This observation is indicative of a well-passivated surface in NSs. In contrast, NSs with identical composition and surface morphology significantly enhance the photoluminescence quantum yields (PLQYs) up to 73%, which represents the highest PLQYs recorded in Cs2NaInCl6 DPs to the best of our knowledge. Beyond fundamental investigations, the study explores the practical applications of these NSs as anti-counterfeit marks created on a flexible substrate, demonstrating robust emission under UV light. Additionally, the fabrication and testing of a light-emitting diode (LED) showcase the versatility of these NSs in optoelectronic devices. This comprehensive exploration of the optical, morphological, and application aspects of Cs₂NaInCl₆ doped with Bi³⁺/Mn2⁺ NSs contributes valuable insights to the evolving landscape of lead-free perovskite materials, highlighting their potential for diverse technological applications.

Thermally Activated Delayed Fluorescence in Organic Semiconductors and Its Application in Light-Emitting Diodes

Thermally Activated Delayed Fluorescence in Organic Semiconductors and Its Application in Light-Emitting Diodes

Analytical study of KOH wet etch surface passivation for III-nitride micropillars

III-Nitride micropillar structures show great promise for applications in micro light-emitting diodes and vertical power transistors due to their excellent scalability and outstanding electrical properties. Typically, III-Nitride micropillars are fabricated through a top-down approach using reactive ion etch which leads to roughened, nonvertical sidewalls that results in significant performance degradation. Thus, it isessential to remove this plasma etch induced surface damage. Here, we show that potassium hydroxide(KOH) acts as a crystallographic etchant for III-Nitride micropillars, preferentially exposing the vertical m-plane, and effectively removing dry etch damage and reducing the structure diameter at up to 36.6nm/min. Both KOH solution temperature and concentration have a dramatic effect on this wet etch progression. We found that a solution of 20% AZ400K (2% KOH) at 90°C is effective at producingsmooth, highly vertical sidewalls with RMS surface roughness as low as 2.59nm, ideal for high-performance electronic and optoelectronic devices.

Effects of Blue and Green Light-Emitting Diode (LED) on the Vegetative and Reproductive Growth of Black Jelly Mushroom (Auricularia auricula-judae)

Effects of Blue and Green Light-Emitting Diode (LED) on the Vegetative and Reproductive Growth of Black Jelly Mushroom (Auricularia auricula-judae)

Impact of photoinduced phase segregation in mixed-halide perovskite absorbers on their material and device stability

Mixed-halide perovskites enable bandgap engineering for tandem solar cell and light-emitting diode applications. However, photoinduced halide phase segregation introduces a compositional instability, that is, formation of I-rich and Br-rich phases, which compromises photovoltaic efficiency and stability. While optical and structural studies of the photoinduced phase segregation in mixed-halide perovskites have been reported, its impact on the material stability is missing. Here, a detailed compositional analysis of mixed-halide perovskite films using x-ray and ultraviolet photoelectron spectroscopy (UPS) was carried out to determine how their stability in various environments depends on the halide ratio. A series of perovskite thin films were fabricated with the composition CH3NH3Pb(IxBr1−x)3, where x = 0.00, 0.25, 0.50, 0.75, and 1.00, and analyzed under different conditions, such as exposure to light in ambient and in nitrogen atmosphere, as well as storage in the dark. From the spectroscopy results, complemented with structural and optical properties, it was found that the deletion of halide ions from the surface is facilitated in mixed-halide perovskites in comparison with pure halide perovskites. A higher stability was found for the mixed-halide perovskite containing less than 25% Br, and it decreases with increasing Br content. This study also established the effect of the Br/I ratio on the energy landscape of the materials. The UPS spectra reveal that photoinduced degradation results in a mismatch of the energy levels at the perovskite/transport layer interface, which may limit the collection of charge carriers. These findings correlate well with the photovoltaic device stability under similar degradation conditions.

Chlorophyl-Passivated Ytterbium-Doped Perovskite Quantum-Cutting Film for High-Performance Solar Energy Conversion and Near-Infrared Light-Emitting Diode Applications.

The quantum cutting ytterbium (Yb3+)-doped CsPbX3 (X = Cl, Cl, or Br) nanocrystals, exhibiting photoluminescence quantum yields (PLQYs) exceeding 100%, hold significant promise for applications in solar energy conversion technologies and near-infrared (NIR) light-emitting diodes (LEDs). This work investigates the usage of chlorophyll (CHL), a naturally existing organic pigment, as an efficient molecular passivator to improve the performance of quantum cutting films. With the assistance of CHL, the resultant perovskite film displays an increased PLQY of 176%. The commercial silicon solar cells (SSCs) with CHL-treated perovskite films demonstrate a remarkable photon-to-current conversion efficiency improvement of 1.83% for a 330.15 cm2 area SSC device. Additionally, a CHL-modified Yb3+:CsPbCl3 film was used to create 988 nm NIR LEDs with an external quantum efficiency of 3.2%. This work provides a new, eco-friendly approach for producing high-quality, large-area Yb3+-doped perovskite film for deployment in photoelectric and night vision applications.

Effects of Light Intensity and Photoperiod on Morphological Development and Photosynthetic Characteristics of Coriander

Coriander (Coriandrum sativum L.) is prized for its aroma and medicinal properties and is extensively employed in various cuisines. Light intensity and photoperiod greatly impact its phenological development. The application of light-emitting diodes (LEDs) in facility cultivation systems enables precise control of lighting conditions, leading to enhanced energy efficiency in coriander cultivation. This study investigated three levels of light intensity (133, 200, and 400 μmol·m−2·s−1) and three photoperiods (8L/16D, 16L/8D, and 24L) to comprehensively assess their effects on coriander’s morphological development, photosynthetic characteristics, and energy utilization efficiency. The objective was to identify a combination conducive to efficient and energy-saving coriander cultivation in PFALs. Results indicated that high light intensity (400 μmol·m−2·s−1) with continuous lighting (24L) reduces coriander’s photosynthetic capacity, while 24-h of continuous lighting can boost yield at the expense of energy efficiency. An 8-h photoperiod significantly decreases the yield compared to 16 h. Low light intensity inhibits plant development, indicating that 133 μmol·m−2·s−1 is suboptimal. For optimal efficiency and yield, a light intensity of 200 μmol·m−2·s−1 and a 16-h photoperiod are recommended in coriander PFAL cultivation. These findings advocate for the adoption of these specific conditions for the indoor cultivation of coriander within PFAL systems.