Blue Light-emitting Diodes Research Articles

Synchronous photocatalytic benzimidazole formation and olefin reduction by magnetic separable visible-light-driven Pd-g-C3N4-Vanillin@γ-Fe2O3-TiO2 Nanocomposite.

A visible light-responsive magnetically separable photocatalyst Pd-g-C3N4-Vanillin@γ-Fe2O3-TiO2 is fabricated using vanillin as a natural junction under ultrasonic agitation. Structural, morphological, optical, thermal, and magnetic assessments of the as-prepared catalyst are carried out. The photocatalyst successfully drives the simultaneous benzimidazole formation, and olefin hydrogenation with high atom economy under blue LED light and mild conditions. The photocatalytic activity of Pd-g-C3N4-Vanillin@γ-Fe2O3-TiO2 is significantly affected by the γ-Fe2O3:TiO2 weight ratio. PL spectra revealed the effective separation of carriers in the fabricated catalyst promoting its photocatalytic activity. The action spectra using the apparent quantum efficiency (AQE) exhibited the maximum AQEs at 520 and 750nm in which the highest performance for styrene hydrogenation is observed. The title magnetically separable heterogeneous photocatalyst provides high yields of products under perfectly safe visible light, produces low/zero waste, and avoids using an external high-pressure hydrogen gas source, harmful solvents, undesirable additives, and reducing agents rendering green conditions for chemical reactions.

Photocatalyzed Aryl C‐H Fluorocarbonylation with CF2Br2

AbstractThe use of abundant and inexpensive fluorine feedstocks to synthesize fluorinated compounds is a promising strategy that has not been extensively investigated. Dibromodifluoromethane (CF2Br2) is an inexpensive fluorine source that has rarely been used for C−H fluoroalkylation. This study reveals an iridium‐catalyzed, tunable strategy for synthesizing acyl fluorides and difluorobromomethylated products using CF2Br2. To achieve the desired products, this process only requires the change of solvent (from DMSO to 1,4‐dioxane) under blue LED illumination. A variety of arenes and heteroarenes with electron‐donating substituents were successfully used, yielding the corresponding products in moderate to good yields. Mechanistic experiments revealed that DMSO served a dual role, functioning as both solvent and nucleophilic reagent in C−H fluorocarbonylation.

Degradation Analysis of Exciplex-Based Organic Light-Emitting Devices Using Carbazole-Based Materials.

A spectral shift and new emission bands in the green and red regions have been observed in deep blue exciplex-based organic light-emitting diodes (OLEDs) using carbazole-based materials, namely, tris(4-carbazoyl-9-ylphenyl)amine (TCTA). To deeply understand the origin of these new bands, single-layer and bilayer TCTA-based OLEDs subjected to electrical and optical (ultraviolet (UV)) stresses were investigated by using various optical, electrical, morphological, and chemical measurements. The results showed that the stress-induced emission bands primarily originate from morphological changes rather than chemical changes. The accumulation of excitons in the TCTA layer induces molecular aggregation, leading to the formation of electrically active electronic states, namely, electroplexes and electromers, which lead to the appearance of additional emission bands in green and red regions. Impedance spectroscopy measurements on single-layer OLEDs complemented this study. The results showed that TCTA degradation affects charge injection and transport. It was concluded that the stress-induced emission bands are caused by aggregate domain formation and are closely linked to the formation of electrically active defects, which act as trap states for charge carriers in the TCTA band gap.

Comparison of BiliCocoon phototherapy with overhead phototherapy in hyperbilirubinemic neonates. A randomized clinical trial.

Around 2-6% of term or late preterm neonates receive phototherapy for hyperbilirubinemia. Standard treatment today is overhead phototherapy. A new device has been developed, the BiliCocoon, where the neonates are "wrapped" presumably making them more comfortable. The aim was to compare the efficacy and performance of the BiliCocoon with overhead LED phototherapy. A randomized open-label multicenter trial in three Danish neonatal units. Healthy hyperbilirubinemic neonates, gestational age ≥33 weeks and postnatal age 24 h to 14 days were randomized to 24 hours' of treatment with BiliCocoon or overhead blue LED phototherapy with an equal level of irradiance. A mixed effect model with random effect by center was used to compare the percentage decrease in total serum bilirubin (TSB) between the treatments. Totally 83 neonates were included. Mean TSB reduction in the BiliCocoon group (N = 42), adjusted for baseline TSB, was significantly lower than in the overhead LED group (N = 41), 29% vs. 38% (p-value < 0.01). Overall difference in temperature by treatment (BiliCocoon vs overhead) was 0.70 [0.37; 1.02] °C, p-value < 0.01. Bilirubin reducing efficacy of BiliCocoon was lower than that of overhead phototherapy, but it was sufficient for nearly all neonates during 24 hours of treatment. The BiliCocoon has a bilirubin reducing efficacy, sufficient for almost all neonates during 24 hours of phototherapy. The BiliCocoon does not have an equal bilirubin reducing efficacy as overhead phototherapy. The duration of light exposure was longer for the neonates treated in the BiliCocoon. A few neonates can be exclusively breastfed in the BiliCocoon throughout the treatment. The reason for stopping breastfeeding in the BiliCocoon was most often, that the neonates developed hyperthermia.

Machine learning and FPGA implementation for predicting luminance decay and temperature distribution in micro-LED displays

AbstractA machine learning-based method predicts the luminance decay of micro light emitting diode (micro-LED) displays, utilizing temperature distribution and degradation experiments alongside implementation on field-programmable gate array (FPGA). Micro-LEDs, used in outdoor and indoor billboards, experience degradation due to harsh environmental conditions. To model temperature distribution in indoor advertising displays using minimal data, a temperature model is constructed based on sensor from the panel and thermal images captured by a camera, in relation to the display pattern. The input data is processed using an FPGA, which transmits the sensed temperatures and display patterns to the micro-LED panel. Multilayer Perceptron (MLP), a type of neural network, predicts the temperature distribution over the panel surface, achieving an error of less than 1.1 °C. Separate degradation models forecast luminance decay, factoring in enclosure temperature, input current, and usage time, with distinct models for red, green, and blue LEDs. Exponential curve-fitting and interpolation, following TM-21 standards, ensure long-term accuracy. The luminance decay predictions have an average error below 1.05% (approximately 9 nits). The FPGA implementation minimizes resource consumption while maintaining prediction accuracy, making it suitable for real-time applications. The degradation model accurately predicts performance over tens or even hundreds of thousands of hours, aligning with the exponential decay trends defined by TM-21.

Determination of Photosensitizing Potential of Lapachol for Photodynamic Inactivation of Bacteria

Antimicrobial photodynamic inactivation (aPDI) offers a promising alternative to combat drug-resistant bacteria. This study explores the potential of lapachol, a natural naphthoquinone derived from Tabebuia avellanedae, as a photosensitizer (PS) for aPDI. Lapachol’s photosensitizing properties were evaluated using Staphylococcus aureus and Escherichia coli strains under blue LED light (450 nm). UV-vis spectroscopy confirmed lapachol’s absorption peak at 482 nm, aligning with effective excitation wavelengths for phototherapy. Photoinactivation assays demonstrated significant bacterial growth inhibition, achieving complete eradication of S. aureus at 25 µg·mL−1 under light exposure. Scanning electron microscopy (SEM) revealed morphological damage in irradiated bacterial cells, confirming lapachol’s bactericidal effect. This research underscores lapachol’s potential as a novel photosensitizer in antimicrobial photodynamic therapy, addressing a critical need in combating antibiotic resistance.

Enhancing the emissive film quality: a new role of TADF materials for high-performance blue perovskite light-emitting diodes

Thermally activated delayed fluorescence (TADF) materials are widely used in the field of organic light-emitting diodes (OLEDs) because they can capture both singlet and triplet excitons for light emission. However, only scare attention has been paid to the application of TADF materials in perovskite LEDs (PeLEDs) and the understanding of effects of TADF materials in PeLEDs is limited. In this study, a new role of TADF materials for achieving high-quality perovskite films to enhance the performance of PeLEDs is emphasized. TADF materials are introduced into quasi-2D blue PeLEDs to assist in the crystallization of perovskites during film annealing and ensure the formation of high-quality films with reduced defects, enhancing device performance. Additionally, a step-like hole transport layer has been constructed to reduce the hole transport barrier, which can further enhance the performance of PeLEDs. The resultant blue PeLEDs exhibits an external quantum efficiency of 5.44%, which is 12.7-fold higher than that of the control device. Furthermore, a turn-on voltage of 2.6 V is achieved, which is the lowest for TADF-based blue PeLEDs. The findings may not only unlock a new role of TADF materials in blue PeLEDs, but also provide an alternative pathway to achieve high-performance PeLEDs.

A Direct Visible‐Light Mediated Coupling Of Azaarenes with Diversely Functionalized Alkyl Carbons via Organophotocatalytic Sp3C−H Bond Activation

AbstractSubstituted azaarenes are one of the most ubiquitous moieties in natural products and drug molecules. An efficient organophotocatalytic method for direct coupling of diverse cyclic and acyclic alkyl carbons of alcohols, ethers, alkyl halides and alkanes with different azaaryl systems has been developed. It uses low loading of easily synthesizable efficient acridinium based photocatalyst and blue LED to generate highly reactive radicals on saturated hydrocarbons through sequential single electron transfer (SET) and hydrogen atom transfer (HAT) process. These in situ generated nucleophilic carbon radicals then undergo instantaneous regio‐selective coupling with azaarenes through Minisci type coupling to generate an array of important pharmacophores through sp2C−sp3C bond formation. With inexpensive organophotocatalysts, higher yield and wide substrate scope, this method provides a greener, efficient and versatile alternative to the previously reported syntheses.

Utilization of Optical OFDM Modulation on Blue LED VLC Datacom Without Equalization for 4 m Wireless Link

To achieve higher visible light communication (VLC) traffic capacity, using the wide bandwidth light-emitting diode (LED) and spectral efficiency modulation signal, is currently the most commonly used method. In this demonstration, we apply the orthogonal frequency division multiplexing quadrature amplitude modulation (OFDM-QAM) with bit- and power-loading algorithm on single blue LED to achieve &gt;1 Gbit/s VLC capacity, when a 400 MHz bandwidth avalanche photodiode (APD)-based receiver (Rx) is exploited for decoding. Here, the higher sensitivity APD can be applied to compensate for the wireless VLC link length in the proposed LED VLC system, and due to the lower LED illumination (255 to 40 lux), is used for the indoor access network after passing the wireless link length of 1 to 4 m. As a result, using single blue LED can achieve 0.962 to 1.057 Gbit/s OFDM rate with available 400 MHz bandwidth APD in poorly illuminated condition indoors without applying analogy equalization.

A wearable and stretchable dual-wavelength LED device for home care of chronic infected wounds.

Phototherapy can offer a safe and non-invasive solution against infections, while promoting wound healing. Conventional phototherapeutic devices are bulky and limited to hospital use. To overcome these challenges, we developed a wearable, flexible red and blue LED (r&bLED) patch controlled by a mobile-connected system, enabling safe self-application at home. The patch exhibits excellent skin compatibility, flexibility, and comfort, with high safety under system supervision. Additionally, we synthesized a sprayable fibrin gel (F-gel) containing blue light-sensitive thymoquinone and red light-synergistic NADH. Combined with bLED, thymoquinone eradicated microbes and biofilms within minutes, regardless of antibiotic resistance. Furthermore, NADH and rLED synergistically improved macrophage and endothelial cell mitochondrial function, promoting wound healing, reducing inflammation, and enhancing angiogenesis, as validated in infected diabetic wounds in mice and minipigs. This innovative technology holds great promise for revolutionizing at-home phototherapy for chronic infected wounds.

Metal-Free Oxidation of Acceptor-Donor Acylhydrazones into Diazo Compounds Using Phenyl Iododiacetate.

Aryl-ester acylhydrazones readily react with phenyl iododiacetate (PIDA) in methanol to produce the corresponding α-diazoesters with good to excellent yields (30 examples). The conditions have also been proven to be efficient in the synthesis of triazolopyridines. The crude mixture containing the diazo compound and acetic acid was also irradiated with low-energy blue LED light for a subsequent one-pot insertion of the in situ-generated carbene with AcOH to afford the respective acetates in high yields.

Synthesis and Properties of a Red Na5Zn2Gd1−x(MoO4)6: xEu3+ Phosphor

Novel Eu3+-doped Na5Zn2Gd(MoO4)6 triple molybdate phosphors were fabricated by the sol-gel method. The structure, morphology, and luminescent properties have been characterized by X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), FTIR spectroscopy, and luminescence spectroscopy. The results indicated that the synthesized Na5Zn2Gd1−x(MoO4)6: xEu3+ phosphor consisted of a pure phase with monoclinic structure. Under excitation at 465 nm, the Na5Zn2Gd1−x(MoO4)6: xEu3+ phosphor exhibits an intensive red emission band around 610 nm corresponding to the transition of 5D0→7F2 which is much higher than that 5D0→7F1 at 594 nm, which was appropriate for a blue LED. According to the influence of the synthesis conditions, the phosphors showed the highest emission intensity when the doping concentration of Eu3+ was 25 mol.% and the molar ratio of citric acid to metal ions was 2:1. Na5Zn2Gd0.75(MoO4)6: 0.25 Eu3+ with the color coordinates (x = 0.658, y = 0.341) is a more stable red phosphor for blue-based white LEDs than the commercial Y2O2S: Eu3+ red phosphor (0.48, 0.50) due to its being closer to the NTSC standard values (0.670, 0.330).

Proposal for Low-Cost Optical Sensor for Measuring Flow Velocities in Aquatic Environments

The ocean, with its intricate processes, plays a pivotal role in shaping marine life, habitats, and the Earth’s climate. This study addresses issues such as beach erosion, the survival of propagules from species like Posidonia oceanica, and nutrient distribution. To tackle these challenges, we propose an innovative sensor that quantifies hydrodynamic velocity by measuring the output voltage derived from detecting changes in light absorption and scattering using LEDs and LDRs. Our results not only demonstrate the effectiveness of the sensor but also the accuracy of the processing algorithm. Notably, the blue LED exhibited the lowest mean relative error of 7.59% in freshwater, while the yellow LED was most precise in chlorophyll-containing water, with a mean relative error of 6.80%. In a runoff simulation, we observed similar velocities with the blue, green, and white LEDs, 6.89 cm/s, 6.99 cm/s, and 7.05 cm/s, respectively, for nearly identical time intervals. It is important to highlight that our proposed sensor is not only effective but also highly cost-efficient, representing less than 0.43% of the cost of a Nortek Vector 6 MHz and 0.18% of the Teledyne Workhorse II 300 kHz Marine. This makes it a key tool for managing marine ecosystems sustainably.

Gradient Hole Injection Inducing Efficient Exciton Recombination in Blue (475 nm) Perovskite QLEDs.

Perovskite quantum dots (QDs) are emerging as excellent light sources for light-emitting diodes (LEDs). However, the performance of blue perovskite QD-based LEDs (QLEDs) still lags behind that of red and green counterparts, which is hindered by blue perovskite QDs with broad bandgaps that tend to increase nonradiative recombination. Here, we designed a gradient energy for hole injection utilizing multiple hole injection layers (HTLs) combined with carbazole-based small-molecule modification to reduce the hole injection barrier between HTLs and QD layers and improve the hole injection efficiency, realizing efficient exciton recombination in blue perovskite QLEDs. Moreover, the QD film on the designed HTLs demonstrates a lower surface roughness and improved photoluminescence properties. The optimized blue CsPbCl3-xBrx QLEDs exhibit an impressive external quantum efficiency of 20.7% with an electroluminescence peak at 475 nm and a turn-on voltage of 2.6 V, representing the state-of-the-art for blue perovskite LEDs emitting in the range of 460-480 nm.

Solvent mediated synthesis of multicolor narrow bandwidth emissive carbon quantum dots and their potential in white light emitting diodes

The development of efficient and environmentally sustainable materials for white light-emitting diodes (WLEDs) is of paramount importance in the field of lighting technology. In this study, we present a solvent-modulated synthesis approach for the fabrication of multicolor narrow-bandwidth emissive carbon quantum dots (CQDs) as a promising solution for constructing WLEDs. The synthesis method involves the controlled reaction of organic precursors in different solvent environments, leading to the formation of CQDs with distinct emission wavelengths with a relatively small full width at half maximum, ranging from 28 to 42 nm. Moreover, these synthesized multicolor CQDs demonstrate a remarkably high fluorescence quantum yield of up to 65%, indicating their potential for constructing efficient WLED when incorporated in polymer matrix and coated on the surface of blue light-emitting diode (LED).

Effect of Peripheral Functionalization of Pt(II) Porphyrin(2.1.2.1) on Singlet Oxygen Generation.

Four structurally bent porphyrin(2.1.2.1) Pt(II) complexes have been obtained and verified well. Main absorbance of Pt(II) porphyrin(2.1.2.1) displayed a significant red-shift compared to that of porphyrin(1.1.1.1) Pt(II) molecules. 1O2 study indicated that electron-withdrawing group and intramolecular charge transfer effect synergistically endowed Pt(II) porphyrin(2.1.2.1) with good singlet oxygen-sensitizing capacity under blue LED light irradiation. This work presents a simple synthesis way to develop a new series of efficient porphyrinoid singlet oxygen photosensitizers for PDT through molecular engineering.

Efficient Visible‐Light‐Induced π‐Extension of Perylene Tetraesters: An Investigation on Regioselectivity

The present study discloses a highly efficient visible‐light‐induced π‐extension of perylene tetraesters and discussion on the regioselectivity in the photocyclization. We initially found that π‐extension reaction of 3,4‐dimethoxyphenyl perylene tetraester smoothly proceeded by only irradiating blue LED with a complete regioselectivity. Investigations of the photocyclization with various substrates revealed the relationship between the regioselectivity and electron‐donating/withdrawing effects of the substituents on the aromatic groups. Moreover, theoretical investigation suggested the importance of bond alteration in the aromatic groups: cyclization proceeds preferentially at shorter C‐C bonds with higher double bond characters. The findings will open new possibilities for the practical synthesis of custom‐designed π‐extended perylene materials.

Bilateral Embedded Anchoring via Tailored Polymer Brush for Large-Area Air-Processed Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) that can be air-processed promises the development of displaying optoelectronic device, while is challenged by technical difficulty on both the active layer and hole transport layer (HTL) caused by the unavoidable humidity interference. Here, we propose and validate that, planting the polymer brush with tailored functional groups in inorganic HTL, provides unique bilateral embedded anchoring that is capable of simultaneously addressing the n phases crystallization rates in the active layer as well as the deteriorated particulate surface defects in HTL. Exemplified by zwitterionic polyethyleneimine-sulfonate (PEIS) in present study, its implanting in NiOx HTL offers abundant nuclei sites of amino and sulfonate groups that balance the growth rate of different n phases in quasi-2D perovskite films. Moreover, the PEIS effectively nailed the interfacial contact between perovskite and NiOx, and reduced the particulate surface defects in HTL, leading to the enhanced PLQY and stability of large-area blue perovskite film in ambient air. By virtue of these merits, present work achieves the first demonstration of the air-processed blue PeLEDs in large emitting area of 1.0 cm2 with peak external quantum efficiency (EQE) of 2.09 %, which is comparable to the similar pure-bromide blue PeLEDs fabricated in glovebox.

Symmetry-Engineered BINOL-Based Porous Aromatic Frameworks for H2O2 Production via Artificial Photosynthesis and In Situ Degradation of Pharmaceutical Pollutants.

Accomplishing visible light-driven H2O2 production at millimolar concentrations is practically challenging, particularly for organic semiconductors. In this context, achieving a maximum H2O2 production rate of 31.60 mmol·g-1·h-1 by using porous aromatic frameworks (PAFs) represents a significant accomplishment. We report the unusual photoactivity of tetraphenylmethane-BINOL-linked PAFs in triplet oxygen activation to facilitate the generation of reactive oxygen species (ROS), as confirmed by their optical and electrochemical responses, despite the absence of a conventional chromophoric moiety. Moreover, an in situ BINOL formation strategy was used to synthesize these PAFs during polymerization in contrast to the reported protocols involving chiral BINOLs as precursors. The as-synthesized polymers had a capsule-like morphology (for TPM-BINOL-6), high thermal stability up to 348 °C, and a high Brunauer-Emmett-Teller (BET) surface area of up to 1382 m2/g (for TPM-BINOL-4). Interestingly, they showed sunlight-driven production of H2O2 via an oxygen reduction reaction of up to 17.05 mmol·g-1·h-1 in 1:10 isopropanol in water for TPM-BINOL-6, which was quantified by titration with ceric sulfate. It also exhibited exemplary photocatalytic efficiency with an H2O2 production rate of 6.65 mmol·g-1·h-1 in seawater. Interestingly, the H2O2 production rate reached a maximum of 18.03 mmol·g-1·h-1 with an SCC efficiency of 4.5% under an AM 1.5G solar simulator and apparent quantum yield (AQY) of 15.8% (at λ = 456 nm) for TPM-BINOL-6 in ethanol:water = 1:10. Moreover, the exceptionally high H2O2 production rate of 31.60 mmol·g-1·h-1 was achieved in 1:1 ethanol in water under 50 W blue LED light. Furthermore, these PAFs generated adequate ROS, which were utilized in the photocatalytic degradation of tetracycline via the superoxide intermediate. Additionally, the as-formed H2O2 was further channelized in the pollution abatement catalytic system for the fast degradation of ciprofloxacin (within 4 h) and the reduction of toxic oxometallate Cr(VI) within 10 min, which is one of the earliest reports of utilizing photosynthesized H2O2 for environmental detoxification.

Photochemically Driven Palladium- Phosphinoacridine Catalysis: A Carboxylative Approach for Arylcarbamate Synthesis.

In this study, we demonstrate that phosphinoacridines are efficient bidentate ligands for palladium-catalyzed carboxylative C-N coupling reactions under blue LED irradiation. This method facilitates the direct synthesis of arylcarbamates using a range of non-activated aryl halides, such as iodides and bromides, with various amines under atmospheric pressure of CO2. The optimized conditions exhibit high tolerance to sensitive functional groups, resulting in very good to excellent yields of the desired products. This approach expands the scope of palladium-catalyzed carboxylation reactions and offers an environmentally friendly route to arylcarbamates.