Application In Light-emitting Diodes Research Articles

Synergistic enhancement of photoluminescence and advanced deep learning model through YOLOv8x in combined effects of carbon dots and Sr₉Al₆O₁₈:Sm³⁺ phosphors

A series of orange-red-emitting Sr₉Al₆O₁₈:Sm³⁺ (1–11 mol %) phosphors are synthesized using the combustion method, while carbon dots (CDs) are produced from urea and citric acid. The incorporation of CDs into the Sr₉Al₆O₁₈:Sm³⁺ (SAO:Sm3+) matrix reduced both negative and positive defects, enhancing the crystallinity of the phosphor. A significant spectral overlap is observed between the emission of CDs and the absorption of SAO:Sm³⁺. An 11.9-folds enhancement in luminescence intensity is detected from the 5 wt% CDs@SAO:Sm³⁺ composite, along with an extended fluorescence lifetime. The energy transfer between CDs and Sm³⁺ is demonstrated, with the increased PL intensity attributed to the Förster Resonance Energy Transfer (FRET) mechanism. The CDs@SAO:Sm³⁺ composites demonstrated excellent selectivity and high contrast when developing latent fingerprints (LFPs). Level I–III structural characteristics of LFPs are easily recognized under ulta violet (UV) light. Furthermore, YOLOv8x, an effective deep learning model, has been modified for the important forensic science task of LFPs recognition. YOLOv8x is able to precisely locate LFPs in complex backgrounds by employing the real-time object detection capabilities of the architecture. With this adjusting, detection speed and accuracy are much increased, making it an effective tool for forensic analysis and law enforcement applications. The optimized orange-red-emitting CDs@SAO:Sm³⁺ composites is synthesized with soluble polyvinyl alcohol (PVA) to produce a transparent anti-counterfeiting ink. The resulting film exhibited excellent flexibility, foldability, and superior thermal and optical properties. In summary, the highly efficient CDs@SAO:Sm³⁺ composite is a versatile luminescent material with multifunctional capabilities, making it ideal for flexible films, LFPs detection, and white light-emitting diodes (w-LEDs) applications.

Synthesis and characterization of machine learning designed TADF molecules

In this study, we present a novel approach to the development of thermally activated delayed fluorescence (TADF) molecules with potentials for organic light-emitting diode (OLED) applications, leveraging machine learning (ML) algorithms to guide the materials design process. Recognizing the imperative for high-efficiency, low-cost emissive materials, we integrated ML driven models with experimental characterization to expedite the discovery of TADF compounds. Initially, a database of ML-designed TADF molecules was employed, with samples being approved to possess optimized photophysical properties. The proposed molecules were synthesized using palladium-catalyzed coupling reactions. Subsequent characterization of these molecules utilized a suite of analytical methods, including nuclear magnetic resonance (NMR) spectroscopy, photoluminescence (PL) spectroscopy, and transient PL decay etc., to confirm their structural integrity and evaluate their performance metrics. The photophysical analysis revealed notable emission efficiencies and significant delayed fluorescence characteristics in solution phases, underscoring the potential of ML-designed TADF molecules. Theoretical validations, through quantum chemical calculations, corroborated the experimental findings, demonstrating the predictive power of our ML models. This interdisciplinary approach not only accelerates the pace of TADF molecule development but also provides a scalable framework for future material innovation especially in the OLED research field.

Synthesis, Characterization and Photoluminescence Studies of near-UV excitable green-emitting NaBaScSi2O7: Eu2+ phosphor with high Internal Quantum Efficiency and Remarkable Thermal Stability

Green-emitting phosphor NaBaScSi2O7:Eu2+ was synthesized by “Amorphous Metal Complex” method using water soluble silicon compound. Eu2+ doped NaBaScSi2O7 exhibited a broad green emission band centered between 500 and 510 nm. The high luminescence intensity of the as-synthesized phosphors may owe to the synthesis procedure based on Amorphous Metal Complex (AMC) method which helps in the homogeneous distribution of Eu2+ ions in the matrix as well as the double annealing in graphite and H2/N2 reducing atmosphere. Upon excitation at 365 nm, the composition-optimized NaBaScSi2O7:Eu2+ exhibited strong green light peaking at 501 nm with the CIE chromaticity (0.146, 0.375) and a high internal quantum efficiency of about 77%. The thermally stable luminescence properties were also studied. The results indicate NaBaScSi2O7:Eu2+ as an attractive candidate for use as a conversion phosphor for Phosphor Converted White light-emitting diode (pc-WLEDs) applications.

Luminescence Behavior and Structural Characteristics of Novel BaYAl3O7: Tb3+ Nanophosphors.

An innovative green emitting novel BaY1 - xTbxAl3O7 (x = 0.02, 0.03, 0.04, 0.05, and 0.06) was synthesized using urea combustion, which was a low-energy process. Using techniques such as photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX) spectroscopy, the structure and luminous properties of the phosphor were investigated. Scherrer's equation was utilized in the XRD technique to determine the crystallite size of the suggested materials. When stimulated with the near-ultraviolet photon, PL spectra revealed intense green emission at 541nm (5D4 → 7F5). The composition with the maximum emission intensity is BaY0.96Tb0.04Al3O7. The dipole-dipole mechanism for concentration quenching events was identified with the help of the critical energy transfer distance. The non-radiative relaxation rate (276s- 1), radiative lifetime (0.75754 ms), and quantum efficiency (79%), of the ideal phosphor composition are calculated using Auzel's model. The color coordinates (0.260, 0.496) align with the emission of green light. The remarkable outcomes validated the significance of the targeted nanocrystals as a superior material with prospective applications in solid-state down-converted white light-emitting diodes (WLEDs).

Ferromagnetic and photoluminescence properties of transparent conductive Cd1-xSnxO thin films for light emitting diode applications

Ferromagnetic and photoluminescence properties of transparent conductive Cd1-xSnxO thin films for light emitting diode applications

Tunable green-blue luminescence of Dy2O3 doped borosilicate glasses for optoelectronic devices

The optical-structural correlated properties of the 40B2O3−40SiO2−10V2O5−(10−x)Fe2O3−xDy2O3 system, where 2, 4, and 6 mol%, were studied. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) confirmed the glassy and amorphous nature of the samples. Adding Dy2O3 promoted the formation of bridging oxygens (upto 4 mol%) by converting BO3 into BO4 units, however, above 4 mol% Dy2O3 act as a modifier. The optical band gap increased from 3.70 to 4.01 eV, while the refractive index decreased from 2.23 to 2.16. The CIE coordinates indicated that the emission spectra fall within the green-blue region. The as-prepared sample exhibited the highest correlated colour temperature value above 5000 K, suggesting its suitability for cool light-emitting diodes sensitive to human vision. These glasses have potential applications in light-emitting diodes and optoelectronic devices.

Impact of Temperature and Substrate Type on the Optical and Structural Properties of AlN Epilayers: A Cross-Sectional Analysis Using Advanced Characterization Techniques.

AlN, with its ultra-wide bandgap, is highly attractive for modern applications in deep ultraviolet light-emitting diodes and electronic devices. In this study, the surface and cross-sectional properties of AlN films grown on flat and nano-patterned sapphire substrates are characterized by a variety of techniques, including photoluminescence spectroscopy, high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and Raman spectroscopy. The results indicate that different sapphire substrates have minimal impact on the photoluminescence spectrum of the epitaxial films. As the temperature increased, the radius of curvature of the AlN films increased, while the warpage decreased. The AlN films grown on nano-patterned substrates exhibited superior quality with less surface oxidation. During the growth of AlN thin films on different types of substrates, slight shifts in the energy bands occurred due to differences in the introduction of carbon-related impurities and intrinsic defects. The Raman shift and full width at half maximum (FWHM) of the E2(low), A1(TO), E2(high), E1(TO), and E1(LO) phonon modes for the cross-sectional AlN films varied with the depth and temperature. The stress state within the film was precisely determined with specific depths and temperatures. The FWHM of the E2(high) phonon mode suggests that the films grown on nano-patterned substrates exhibited better crystalline quality.

Emergent updates and future directions on white light emitting diodes based on luminous lead-free halide perovskites

Lead halide perovskites possess exceptional optical and electrical properties, yet their inherent toxicity and instability present significant challenges for practical application in white light-emitting diodes (WLEDs) for displays and lighting. Alhough, techniques such as reduced dimensionality, transition metal doping, and protective encapsulation have shown some success in enhancing stability. These advancements remain limited and do not fully meet the requirements for real-world WLED devices. This featured letter delves into the emerging advancements in lead-free halide perovskite WLEDs includes color-conversion WLEDs, and single-emissive-layer WLEDs. Despite significant advancements, issues with stability, efficiency, and scalable fabrication still exist. Future approaches centre on methods to enhance these features, opening the door for lead-free perovskite WLEDs to become commercially viable and bringing in a new age of environmentally friendly lighting options. Additionally, this featured letter provides a comprehensive review of the current advancements and future possibilities in WLEDs based on lead-free halide perovskites materials. This letter serves as an invaluable resource for researchers, scientists, and engineers dedicated to advancing this field.

Progress, application and prospect of rare earth-based perovskite light-emitting diodes

Perovskites recently become star materials in light-emitting diodes (LEDs) field due to their high color purity, tunable emission spectra, and cost-effectiveness. However, the commercial applications of perovskite LEDs are hampered by inferior lattice stability of perovskite materials. Successful modification of functional materials is a promising strategy towards efficient and stable perovskite LEDs. Rare earth (RE) metals are incorporated into the perovskite lattice, including double perovskites, by occupying the B-site or A-site in perovskite such as ABX3 or A2BB'X6, forming the RE-based perovskite. Doping with RE ions enables precise control emission color of materials across a broad spectrum ranging from ultraviolet to near infrared. Moreover, this strategy reduces the energy loss in electron relaxation process and enhances electroluminescence intensity of LED device, thereby improving the potential of commercial applications of perovskite LEDs. This review provides a comprehensive and systematic summarization of recent progress and challenges in RE-based perovskite materials (structure types, luminescence mechanism and synthesis methods) and LEDs (device structures and main applications) to provide some enlightening insights for realization of efficient and stable RE-based perovskite LEDs.

Rectified electrical transport and self-powered photoresponse in ZnTe/WS2 heterostructures

Semiconductor heterostructures have attracted widespread attention due to their applications in light-emitting diodes, solar cells, and photodetectors. In this work, a novel heterostructure consisting of ZnTe nanobelt and WS2 monolayer nanosheet was constructed by combining physical transfer with vapor deposition routes. The I-V curve of ZnTe/WS2 heterostructure device displays a rectification ratio of approximately 50, which can be attributed to the formation of PN junction. The derived photovoltaic effect enables self-powered photodetection. Additionally, light imaging measurements show that the achieved ZnTe/WS2 Photodetectors have good imaging capabilities under 405 nm light irradiation. These results reveal that such ZnTe/WS2 heterostructures are excellent candidates for optoelectronic applications.

Green synthesis of 2-trifluoromethylquinoline skeletons via organocatalytic N-[(α-trifluoromethyl)vinyl]isatins C-N bond activation

The Pfitzinger reaction has long served as a notable synthesis pathway for quinoline-4-carboxylic acids. Although recognized for its synthetic potential since its discovery more than 138 years ago, a truly catalytic variant has remained elusive until now. Herein, we present a novel 2-tert-butyl-1,1,3,3-tetramethylguanidine (BTMG)-catalyzed Pfitzinger reaction that employs N-[(α-trifluoromethyl)vinyl]isatins with amines and alcohols, providing direct routes to 2-CF3-quinoline-4-carboxamides and carboxylic esters. This method is not only green and environmentally benign but also accommodates the introduction of other functional groups like CF2H and CO2Me at the C2 position of quinoline skeleton. The utility of this methodology was demonstrated by the broad substrate scope, the late-stage modification of commercial drugs, and the diverse derivatization of quinoline framework. More importantly, this work not only opens up a new avenue for the activation of amide C-N bonds in catalytic reaction development, but also unlocks the huge potential of some 2-trifluoromethyl quinolines with strong inhibitory activity against PTP1B or optoelectronic application in organic light-emitting diodes.

Investigation on dysprosium (Dy3+) doped lithium boro-phosphate glass for light-emitting diode (LED) and supercapacitor applications

Investigation on dysprosium (Dy3+) doped lithium boro-phosphate glass for light-emitting diode (LED) and supercapacitor applications

Enhanced luminescence of CaO:Eu2+ red phosphor in glass for high-power warm LED

Highly emissive and stable red phosphors are vital for the warm Light Emitting Diode (LED). Herein, blue-light-excited CaO:Eu2+ red phosphors were prepared using the carbonation method, coupled with the double crucible carbon reduction technology. The addition of GeO2 and SnO2 significantly enhanced the photoluminescence (PL) intensity and quantum efficiency. Furthermore, a phosphor-in-glass (PiG) made from an improved luminescent CaO:Eu2+ was developed and utilized for LED applications. Such PiG samples considerably improved the stability of CaO:Eu2+ phosphors. The excellent stability, high color rendering index (Ra) value of 87.7 and low correlated color temperature (CCT) of 4469 K confirmed the resulting CaO:Eu2+-based PiG as a promising material for white light-emitting diodes (WLEDs).

Light-emitting diode-based absorbance detectors for flow-through analysis in analytical chemistry: A tutorial

The development of light-emitting diodes (LEDs) has played a significant role supporting many recent advances made in chemical analysis. Their small size, low power consumption, and semi-monochromaticity make them ideal light sources for portable photometric devices used in field and on-site analysis, environmental monitoring, and industrial applications, such as process analytical technology (PAT) and continuous real-time analysis. This tutorial provides an overview and critical comparison of the key components in LED-based absorbance detectors, including light sources, optical fibres, flow cells, and photodetectors. Fundamental aspects of LEDs relating to their use in such simple detectors are discussed in detail, along with the development of multi-wavelength detectors that incorporate multiple LEDs. The tutorial also details the different methodologies for assessing and characterising the LED-based absorbance detectors. Finally, this tutorial presents some selected applications of LED based photometric detectors in gas sensing, flow injection analysis (FIA), and coupled with separation techniques such as ion chromatography, liquid chromatography, and capillary zone electrophoresis (CZE).

Lanthanide Functionalized Carbon Quantum Dots for White Light Emission, pH Sensing, and Co (II) Detection.

Carbon quantum dots (CQDs) with fluorescence emission have been widely studied for versatile applications, but facile tunability of the spectral properties of CQDs by doping remains to be further explored. Herein, employing lanthanide ion Eu3+ as a dopant and activator, a simple and efficient synthesis route for pure CQDs and Eu-CQDs was demonstrated using N, N-dimethylformamide, oleic acid, and oleylamine as precursors for carbon sources. In comparison, with the popular citric acid precursor, the as-prepared CQDs and Eu-CQDs exhibited an obviously smaller particle size (1.72 ± 0.29 nm) and a more uniform distribution. Through systematic optimization of Eu3+ doping for the Eu-CQD system, colorful light emissions in the visible range were first realized under excitation of ultraviolet (UV) ∼360 nm for promising application of UV-triggered light-emitting diodes. Most interestingly, this Eu-CQD solution with UV-excited colorful light emissions was utilized as a visual pH sensor, experimentally featuring good repeatabilities and stabilities (pH values switching between 7 and 14). Besides, the Eu-CQD solution exhibited highly sensitive detection characteristics for Co (II) ions. Due to the spectral overlapping, the quenching efficiency is as high as 96.3%, and the detection limit is obtained as 0.139 μM, which is much lower than the maximum concentration of Co (II) in the drinking water permitted by WHO. All of these relevant results significantly demonstrate the great potential of lanthanide doping in the multifunctionalization of CQDs for certain emerging applications like lighting, sensing, and detection.

Quantifying Efficiency Roll-Off Factors in Quantum-Dot Light-Emitting Diodes.

The application of quantum-dot light-emitting diodes (QLEDs) is hindered by efficiency roll-off at high current densities. Factors contributing to this roll-off include Auger recombination, electric field-induced quenching, Joule heating, and electron leakage into the hole transport layer. However, a method to quantitatively attribute the contribution of each factor to roll-off has not yet been available, leaving the primary cause of roll-off unidentified. This work addresses this gap using electrically pumped transient absorption spectroscopy, which measures the accumulated electrons and electric field in quantum dots (QDs). This study also introduces a method to quantify electron leakage in QLEDs using this spectroscopic technique. Based on the spectroscopic experimental results, the contribution of each factor to roll-off is quantified. A green QLED with a peak external quantum efficiency (EQE) of 26.8% is studied as an example. The EQE declines to 20.5% at a current density of 354mA cm-2, where field-induced quenching accounts for 5% of the efficiency roll-off, and electron leakage contributes 95%. Contributions from Auger recombination and heat-induced quenching are negligible. This work demonstrates strong correlations between roll-off and electron leakage amplitude using statistical data obtained in multiple QLEDs, confirming that electron leakage is the primary factor in EQE roll-off.

Lateral Diffusion of Holes in Anodic Buffer Layers and Its Application in Organic Light-Emitting Diodes

Lateral Diffusion of Holes in Anodic Buffer Layers and Its Application in Organic Light-Emitting Diodes

Optimizing ZnSe nanorods with La doping for structural, electrical, and dielectric properties in device applications

Nano-materials, pure Zinc Selenide (ZnSe), and rare earth (Lanthanum) doped ZnSe (Zn1-xLaxSe, x = 0.00, 0.02, 0.04, 0.06) were synthesized via a facile and low-cost hydrothermal method. X-ray diffraction (XRD) demonstrated that the nanoparticles grow in cubic crystal phase with high degree crystallinity, and the measured crystallite size of La-doped ZnSe ranges from 31.95 to 31.11 nm. Mitigation in crystallite size was observed with the inclusion of La and enhancement in the lattice constant ‘a’ from 5.6565 Å to 5.6818 Å. Morphological study (FESEM) depicts synthesized materials' morphologies as nanorods. The FESEM images indicate the random distribution of the nanorods across the crystal lattice, regardless of the accumulation of the nanorods, showing lumps in the synthesized material sample. The estimated grain size of pure ZnSe nanorods ranges from 137.6 to 496.9 nm. Electrical features revealed that direct current (DC) electrical conductivity ‘σdc’ enhances with temperature, affirming the semiconducting behavior of the materials. Increased lanthanum content enhances the ‘σdc’ from 3.08 × 10–5 (Ω cm)-1 to 5.94 × 10–5 (Ω cm)-1 at 303 K while lessening the activation energy value from 0.134 to 0.104 eV. Dielectric features, including relative permittivity (ε'), loss factor or dielectric loss (ε''), tangent loss (tanδ), as well as AC conductivity (σac), indicate a direct proportionality with temperature, and elevated values of all the dielectric parameters are noted with La-doping. An increase in dielectric constant with doping concentration displayed that the prepared nanocrystals have valuable dielectric and capacitive behavior. The outcomes of electrical and dielectric features display that the prepared nanorods have vital characteristics for developing optoelectronic devices, solar cells, photocatalysts, and light-emitting diode applications.

Blue Light-Emitting Diodes Based on Pure Bromide Perovskites.

Blue perovskite light-emitting diodes (LEDs) are essential for the creation of full-color displays and white-light illumination, and some significant progress is made in recent years. However, most high-performance blue perovskite LEDs are currently based on mixed-halide perovskites and suffer from unstable spectra due to inevitable halide phase segregation, which is unfavorable for the application of blue perovskite LEDs. In contrast, blue emissions from pure bromide perovskites generally exhibit stable spectra (consistent emission peak positions and spectral shapes) and are worthy of attention. In this review, the recent advances in blue LEDs based on pure bromide perovskites according to different strategies are classified and summarized. Moreover, the challenges related to poor charge injection, high defect-state density, lack of high-performance in the deeper blue region, and inferior operational stability are addressed. Finally, an outlook is provided on feasible future research directions for highly bright, efficient, and stable blue perovskite LEDs.

Improving Inoculum Production of Arbuscular Mycorrhizal Fungi in Zea mays L. Using Light-Emitting Diode (LED) Technology

A substrate-based production system is a simple and low-cost method for arbuscular mycorrhizal (AM) fungal inoculum production. However, it is time-consuming and typically yields low numbers of AM fungal spores due to several factors affecting plant growth efficiency. Our study investigated the use of light-emitting diode (LED) technology to expedite AM fungal spore production in planta. We performed experiments with Rhizophagus irregularis inoculated in maize (Zea mays L.), contrasting LED light with greenhouse (GH) conditions. Our results exhibited a significant improvement in AM fungal colonization and spore production, as well as a reduction in the production period from 120 to 90 days under the LED light condition. This was achieved using a red-and-blue light ratio of 60:40 with a total light intensity of 300 µmol m−2 s−1. The LED light treatments improved maize growth by increasing nitrogen (N) and phosphorus (P) concentrations in shoots and roots, respectively. Our gene expression analyses revealed that in AMF-inoculated plants, genes related to photosynthesis were significantly upregulated under LED light compared to the GH condition. Moreover, LED increased the expression of marker genes linked to the AM fungi-related cell cycle, indicating enhanced AM fungal growth during symbiosis. These findings advance our comprehension of LED applications in agriculture, offering promising prospects for acceleration of AM fungal spore production.