Light-emitting Diodes Research Articles

Photodegradation of Dacarbazine Catalyzed by Vitamin B2 and Flavin Adenine Dinucleotide Under Visible-Light Irradiation.

Drug photodegradation is a matter of great concern because it can result in potency loss and adverse side effects. This study examines the light-induced degradation of dacarbazine catalyzed by vitamin B2 and flavin adenine dinucleotide (FAD) under light-emitting diode (LED) or fluorescent light irradiation. Dacarbazine was irradiated with LED (405nm) or fluorescent light in the presence of various equivalents of vitamin B2 or FAD. The photodegradation of the drug in D2O was monitored by 1H nuclear magnetic resonance spectroscopy. Dacarbazine dissolved in D2O decomposed in the presence of vitamin B2 or FAD under irradiation with LED or fluorescent light. The decomposition products were 2-azahypoxanthine 2, which has previously been observed after light irradiation in the absence of vitamin B2, and 1H-imidazole-5-carboxamide 6, a new product formed in the presence of vitamin B2. Irradiation with LED light was more effective than irradiation with fluorescent light in degrading dacarbazine. Vitamin B2 and FAD induced dacarbazine photodegradation. Thus, the interfusion of vitamin B2 or FAD under excessive light exposure should be avoided during the intravenous administration of dacarbazine.

Development of blue-light GaN based micro light-emitting diodes using ion implantation technology

This study fabricated 10 μm chip size μLEDs of blue-light GaN based epilayers structure with different mesa processes using dry etching and ion implantation technology. Two ion sources, As and Ar, were applied to implant into the LED structure to achieve material isolation and avoid defects on the mesa sidewall caused by the plasma process. Excellent turn-on behavior was obtained in both ion-implanted samples, which also exhibited lower leakage current compared to the sample fabricated by the dry etching process. Additionally, lower dynamic resistance (Rd) and series resistance (Rs) were obtained with Ar implantation, leading to a better wall-plug efficiency of 10.66% in this sample. Consequently, outstanding external quantum efficiency (EQE) values were also present in both implant samples, particularly in the sample implanted with Ar ions. This study proves that reducing defects on the mesa sidewall can further enhance device properties by suppressing non-radiative recombination behavior in small chip size devices. Overall, if implantation is used to replace the traditional dry etching process for mesa fabrication, the ideality factor can decrease from 11.89 to 2.2, and EQE can improve from 8.67 to 11.03%.

Highly Efficient and Linearly Polarized Light Emission of Micro-LED Integrated with Double-Functional Meta-Grating.

Linearly polarized micro light-emitting diodes (LP-Micro-LEDs) exhibit exceptional potential across diverse fields. The existing methods to introduce polarization to initially unpolarized Micro-LEDs and to further enhance the degree of polarization are, however, at the expense of low luminous efficiency. We fabricated a GaN-based blue Micro-LED integrated with a Al nanograting and a specially designed Ag/GaN meta-grating, which overcomes the dilemma between the luminous efficiency and polarization degree by simultaneously introducing the effects of mode selection and energy recycling. The fabricated LP-Micro-LED achieves an average polarization extinction ratio (ER) of 21.92 dB within ±60°, showing a 2.04-fold increase in efficiency and a 1.32-fold increase in ER compared to the Ag reflector design. This approach opens the way toward the next generation of high-efficiency and low-cost optoelectronic devices in encryption, displays, optical communication, and medicine.

Photodynamic Inactivation of Human Herpes Virus In Vitro with Ga(III) and Zn(II) Phthalocyanines

Photodynamic inactivation (PDI) has been revealed as a valuable approach against viral infections because of the fast therapeutic effect and low possibility of resistance development. The photodynamic inhibition of the infectivity of human herpes simplex virus type 1 (HSV-1) strain Victoria at different stages of its reproduction was studied. PDI activity was determined on extracellular virions, on the stage of their adsorption to the Madin-Darby bovine kidney (MDBK) cell line and inhibition of the viral replication stage by application of two tetra-methylpyridiloxy substituted gallium and zinc phthalocyanines (ZnPcMe and GaPcMe) upon 660 nm light exposure with a light-emitting diode (LED 660 nm). The PDI effect was evaluated on extracellular virions and virus adsorption by the terminal dilution method and the change in viral infectivity, which was compared to the untreated control group. The decrease in viral titer (Δlgs) was determined. The effect on the replicative cycle of the virus was determined using the cytopathic effect inhibition (CPE) assay. The direct influence on the virions showed a remarkable effect with a decrease in the viral titer more than 4 (Δlg > 4). The influence of the virus to the cell on the stage of adsorption was also significantly affected by the exposure time and the concentration of applied photosensitizers. A distinct inhibition was evaluated for ZnPcMe at the viral replication stage, which demonstrated a high photoinactivation index (PII = 33.0). This study suggested the high efficacy of PDI with phthalocyanines on HSV-1 virus, with full inhibition caused by the mechanism of singlet oxygen generation. These promising data are a good basis for further investigations on the PDI application against pathogenic viruses.

Enhanced Efficiency and Delayed Decay of Organic Light-Emitting Diodes by Incorporating Spacer Layer Based on Low-Triplet Energy Interfacial Exciplex

Enhanced Efficiency and Delayed Decay of Organic Light-Emitting Diodes by Incorporating Spacer Layer Based on Low-Triplet Energy Interfacial Exciplex

Realizing Highly Stable Quasi-2D Blue Perovskite Light-Emitting Diodes Using Energy Cascades Generated by Biomolecule-Derived Plasmonic Nanostructures.

Blue perovskite light-emitting diodes (LEDs) lag behind green and red LEDs, which have made considerable strides in efficiency and stability. The main disadvantage is its unmodulated phase domains and low energy transfer efficiency, which impede the efficiency, optical purity, and operational stability of the devices. Herein, we show that using biomolecule-derived plasmonic nanostructures can significantly promote defect passivation, van der Waals gap reduction, and cascade energy transfer through synergistic small-molecule interactions and localized surface plasmonic contributions, thereby improving the electroluminescence (EL) properties and operational stability. The designed blue quasi-2D perovskite LED benefits from the synergistic effect with a higher external quantum efficiency (EQE = 3.51%), EL spectral stability, and superior long-term operational stability. These results validate the optimization of structural and energy cascades of quasi-2D perovskites through a simple and environmentally friendly biomolecular tailorable plasmonic nanostructure approach, paving the way for the development of sustainable electronics.

Trivalent Rare Earth Ion‐Doped Metal Halide Perovskite Near‐Infrared Semiconductors for High‐Performance Optoelectronic Devices

AbstractGiven the extensive application of near‐infrared (NIR) emission, the quest for efficient and versatile NIR semiconductors have attracted tremendous attention. Leveraging trivalent rare earth (RE3+) ions doping, the integration of metal halide perovskites with RE3+ ions makes it easy to achieve NIR‐II emission (1000–1700 nm). However, although showing promise in bioimaging, optical communication, and night vision, enhancing NIR‐II emission intensity to promote further progress in real‐world applications remains a challenge. This review summarizes the recent advancements in RE3+ ion‐doped perovskite NIR semiconductors, and discusses what kind of properties are needed and how to achieve desired optical properties in various applications. The review starts with the synthesis methods for various material types with rich examples. Following this, the mechanisms of strategies for optimizing NIR luminescence performance are discussed in detail. Furthermore, the review highlights their multifunctional applications both as an electrically driven emitter in NIR light‐emitting diodes (LEDs) and as a down‐conversion emitter in photovoltaic devices (PVs) or phosphor‐converted LEDs (pc‐LEDs). Finally, insights on how to fill the gap between current research and future goals are provided. This review aims to provide a deeper understanding of RE3+ ion‐doped NIR light‐emitting perovskite materials, and to promote the exploration of efficient NIR emitters.

Ultra-thin p-AlGaN insert layer for enhancing the electrical performance of AlGaN-based deep-ultraviolet light-emitting diodes

A composite p-contact structure is proposed to enhance the electrical performance of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs). With the insertion of a 1 nm-thick p-AlGaN layer prior to the contact layer, the operating voltage at 100 mA is significantly reduced by 0.2–0.3 V in 277 nm DUV-LEDs, leading to a maximum wall-plug efficiency of 10.7%. It is experimentally demonstrated that the reduction of operating voltage is mainly attributed to the lower specific contact resistivity of p-contact. The improvement mechanism of contact property is further explored by the theoretical calculations of energy band, where the hole accumulation in the contact layer, owing to the greater valence band offset induced by the p-AlGaN insert one, is speculated to promote the tunneling at the metal/semiconductor interface. The composite p-contact structure in this study is compatible with the present commercial DUV-LED epitaxial structure, enabling it to promote further development of this field.

"Impossible Trinity" between Efficiency, Stability, and Color Purity for Blue OLEDs: Challenges and Opportunities.

Organic light-emitting diodes (OLEDs) have become the cutting-edge technology in the display market. However, compared with green and red stacks, blue stacks still remain an obstacle for OLED technology. There seems to be an "impossible trinity" between efficiency, stability, and color-purity for blue OLEDs. In this trilemma, advances in device stability have lagged far behind. In this Perspective, focusing on the critical role of bond-dissociation energy (BDE), we first summarize recent advances in the chemical degradation mechanism of high-efficiency blue OLED materials and then highlight strategies to improve the intrinsic stability and device lifetime from the material point-of-view. Finally, future challenges and opportunities for developing robust blue OLED materials and devices are envisioned, including the rational design of robust blue materials with high BDEs, two-pronged approaches from both thermodynamic and kinetic aspects, the great need for robust host materials, deep insights into host-guest interactions, collaborative efforts from the aspect of devices, and data-driven screening and iteration development.

Impact of different light curing mode on post-operative hypersensitivity after Class I composite restorations: A randomized clinical trial

The main challenges encountered when using direct composite resins are, polymerization shrinkage and shrinkage stress, the degree of polymerization conversion, and their limited depth of cure. To overcome these challenges soft start light curing mode is preferred nowadays. To evaluate the occurrence of post-operative hypersensitivity in Class I composite restorations comparing the soft-start with the constant light curing modes using 7 generation bonding agent.Twenty patients with each having contra lateral Class I occlusal caries lesions in molars were participated. Forty Class I cavity preparations were restored with 7th generation bonding agent 7generation bonding agent (Scotchbond Universal Adhesive (3M ESPE, St Paul, USA)) and 3M™ Filtek™ Bulk Fill Flowable Restorative (3M ESPE, St Paul, USA). For each patient, one restoration was cured with soft-start mode and the contralateral restoration was cured with constant curing modes using Light Emitting Diode (LED) curing light. POH was evaluated at day 1,2&7 post-treatment using Visual Analog Scale (VAS). Data were collected and analysed by ANOVA test. Statistically significant differences were observed between the two curing modes in occurrence of postoperative hypersensitivity (P<0.05). Statistical analysis revealed that incidence of POH were higher at day 1 and day 2 in constant light curing group as compared with soft start light curing group which were reduced at day 7 in both groups. Incidence of POH is seen less in soft start curing mode as compared with constant light curing mode. To reduce post-operative hypersensitivity soft start light curing mode should be used.

Tunable Optical Properties, Enhanced Photoluminescence, and Thermostability of CaO: Eu2+/3+ Phosphors by Codoping Cl- Ions.

Europium-activated calcium oxide (CaO: Eu) phosphor shows great potential in the fabrication of light-emitting diodes (LEDs). However, its luminescent intensity and thermostability still need to be further enhanced. In this work, the photoluminescence property and thermostability of CaO: Eu2+/3+ were improved significantly by codoping a few of Cl- ions into it. Compared with CaO: Eu2+/3+ samples, CaO: Eu2+/3+, Cl- phosphors not only have tunable luminescence but also show stronger luminescence intensity and thermal stability. The emission color of phosphors can be tuned by changing the excitation wavelength; typically, strong red/blue light can be displayed under 250/362 nm excitation. More importantly, both the red and blue emissions will increase simultaneously with increasing codoped Cl- content. When the Cl- ion content is 0.06, the emission intensity of CaO: 0.01Eu2+/3+, 0.06Cl- reaches its maximum and its red and blue emission intensities increase by approximate 2.5 times and 13.2 times, respectively. The results show that CaO: Eu2+/3+, Cl- phosphors have potential application value in LEDs and anti-counterfeiting.

The Golden Age of Thermally Activated Delayed Fluorescence Materials: Design and Exploitation.

Since the seminal report by Adachi and co-workers in 2012, there has been a veritable explosion of interest in the design of thermally activated delayed fluorescence (TADF) compounds, particularly as emitters for organic light-emitting diodes (OLEDs). With rapid advancements and innovation in materials design, the efficiencies of TADF OLEDs for each of the primary color points as well as for white devices now rival those of state-of-the-art phosphorescent emitters. Beyond electroluminescent devices, TADF compounds have also found increasing utility and applications in numerous related fields, from photocatalysis, to sensing, to imaging and beyond. Following from our previous review in 2017 ( Adv. Mater. 2017, 1605444), we here comprehensively document subsequent advances made in TADF materials design and their uses from 2017-2022. Correlations highlighted between structure and properties as well as detailed comparisons and analyses should assist future TADF materials development. The necessarily broadened breadth and scope of this review attests to the bustling activity in this field. We note that the rapidly expanding and accelerating research activity in TADF material development is indicative of a field that has reached adolescence, with an exciting maturity still yet to come.

Efficient Circularly Polarized Electroluminescence Enabled by Low-Dimensional Bichiral Perovskite Nanocrystals.

Chiral organic-inorganic hybrid perovskite nanocrystals have gained attention as promising materials for circularly polarized luminescence emission, owing to their high photoluminescence efficiency and superior charge-carrier mobility. However, achieving circularly polarized electroluminescence (CPEL) from mixed-phase perovskite nanocrystals remains a significant challenge. We present bichiral formamidinium lead bromide (FAPbBr3) nanocrystals that achieve room-temperature circularly polarized light-emitting diodes (LEDs) via a synergistic effect between a chiral interior spacer (methylbenzylamine cation, MBA+) and a chiral surface ligand (camphorsulfonic acid, CSA). The incorporation of MBA+ induces chiral crystal lattices, while CSA ligands, featuring sulfonate groups, effectively passivate defects, suppress exciton spin-flip, and enhance conductivity. The resulting circularly polarized LEDs exhibit an enhanced electroluminescence asymmetry factor (gEL) of ∼2 × 10-3, along with an external quantum efficiency (EQE) of 3.1%. These bichiral nanocrystals represent a significant advancement in luminescence efficiency and enantioselectivity, indicating their potential for next-generation chiroptoelectronic applications.

A Tailored TADF Emitter Based on Diphenylacetylene Anthracene Derivatives for Highly Efficient Solution-Processed Pure Red Organic Light-Emitting Diodes.

It holds enormous significance for red thermally activated delayed fluorescence (TADF) emitters to develop organic light-emitting diodes (OLEDs) with high efficiency and high color purity, which remains challenging for highly efficient solution-processed red TADF emitters due to the limitation of severe nonradiative decays. Herein, a red TADF emitter containing space interactions, 4,4'-(9,10-bis(phenylethynyl)anthracene-1,8-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (DBP-2MOTPA), is designed and synthesized, composed of ethynyl as the acceptor and methoxytriarylamine (MOTPA) as the donor. The triphenylamine donor unit decorated with peripheral methoxy units not only improves the solubility for the solution-processed technology but also increases the electron-donating ability. The highly twisted donor-π-acceptor (D-π-A) architecture generates a small energy gap (ΔEST) of 0.14 eV, and the appropriate overlap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) leads to a supernal photoluminescence quantum yield (ΦPL) of 68%. Consequently, the nondoped device based on DBP-2MOTPA with Commission Internationale de l'Eclairage (CIE) at (0.67, 0.33) exhibits the pure red emission, which satisfies the Rec.1931 standard red gamut (0.67, 0.33) and approaches the Rec.2020 standard (0.71, 0.29). Moreover, the doped devices employing DBP-2MOTPA as the emitter exhibit a maximum external quantum efficiency (EQE) of 6.09%, which is among the effective values in the solution-processed red TADF-OLEDs.

Single Solid‐State Emissive Carbon Quantum Dots for Multicolor, Bright and Efficient Electroluminescent Light‐Emitting Diodes

Color‐tunable electroluminescent light‐emitting diodes (LEDs) based on quantum dots (QDs) are rapidly emerging as a key technology for next‐generation full‐color displays and solid‐state lighting. However, achieving broad color tunability in LEDs that utilize a single QD emissive material continues to pose significant challenges. Here, we present the first example of bright, multicolor electroluminescent LEDs with tunable emission peaks spanning from 535 to 640 nm, utilizing a new type of single red solid‐state emissive carbon quantum dots (R‐SSCQDs). Unlike conventional CQDs, which often exhibit weak or negligible emission in solid‐state form, R‐SSCQDs demonstrate bright red emission in solid state and green emission in diluted state. Experimental investigations and theoretical calculations reveal that the unique non‐planar spatial structure and significant steric hindrance of R‐SSCQDs effectively suppress π‐π stacking, resulting in efficient solid‐state fluorescence emission. By adjusting the weight ratios of R‐SSCQDs doped in host materials, we showcase bright, efficient and multicolor CQD‐based LEDs that emit green, yellow, orange, and red light, achieving a record‐high luminance of 15,834 cd m‐2 and current efficiency of 10.3 cd A‐1. This work presents a straightforward and universal strategy for creating efficient solid‐state emissive CQDs, showcasing significant potential for color‐tunable LED applications.

Single Solid-State Emissive Carbon Quantum Dots for Multicolor, Bright and Efficient Electroluminescent Light-Emitting Diodes.

Color-tunable electroluminescent light-emitting diodes (LEDs) based on quantum dots (QDs) are rapidly emerging as a key technology for next-generation full-color displays and solid-state lighting. However, achieving broad color tunability in LEDs that utilize a single QD emissive material continues to pose significant challenges. Here, we present the first example of bright, multicolor electroluminescent LEDs with tunable emission peaks spanning from 535 to 640 nm, utilizing a new type of single red solid-state emissive carbon quantum dots (R-SSCQDs). Unlike conventional CQDs, which often exhibit weak or negligible emission in solid-state form, R-SSCQDs demonstrate bright red emission in solid state and green emission in diluted state. Experimental investigations and theoretical calculations reveal that the unique non-planar spatial structure and significant steric hindrance of R-SSCQDs effectively suppress π-π stacking, resulting in efficient solid-state fluorescence emission. By adjusting the weight ratios of R-SSCQDs doped in host materials, we showcase bright, efficient and multicolor CQD-based LEDs that emit green, yellow, orange, and red light, achieving a record-high luminance of 15,834 cd m-2 and current efficiency of 10.3 cd A-1. This work presents a straightforward and universal strategy for creating efficient solid-state emissive CQDs, showcasing significant potential for color-tunable LED applications.

High-Temperature Polymorphism and Band-Gap Evolution in BaZrS3.

Barium zirconium trisulfide (BZS) is a three-dimensional (3D) perovskite with optoelectronic properties suitable for photovoltaic (PV) and light-emitting diode (LED) applications that is conventionally reported in the orthorhombic Pnma (62) symmetry. Synchrotron X-ray diffraction, thermal analysis, and Raman and absorption spectroscopy revealed three high-temperature polymorphs that appear when BZS is heated in air prior to complete oxidation (BaZrS3 + 5O2 → BaSO4 + ZrO2 + 2SO2↑) at 700 °C with the approximate stability ranges: BaZrS3 IVPnma (62)T < 400 °CBaZrS3 IIICmcm (63)400 °C ≤ T ≤ 500 °CBaZrS3 II14/mcm (140)500 °C ≤ T ≤ 700 °CDifferential scanning calorimetry (DSC) revealed exothermic features accompanying the IV → III and III → II phase changes. Furthermore, the direct band gap varied inversely with temperature with distinct energies for each polymorph (1.84 eV ≤ IV ≤ 1.65 eV; 1.65 eV ≤ III ≤ 1.54 eV; 1.54 eV ≤ II ≤ 1.52 eV). Raman spectroscopy found that polymorphic changes up to 600 °C were reversible with bands characteristic of BaZrS3 IV entirely restored upon cooling to room temperature (RT). This more complete understanding of BSZ polymorphism provides a basis for producing crystallochemical variants with enhanced optoelectronic properties under ambient conditions.

High-Performance Green and Blue Light-Emitting Diodes Enabled by CdZnSe/ZnS Core/Shell Colloidal Quantum Wells.

The unique anisotropic properties of colloidal quantum wells (CQWs) make them highly promising as components in nanocrystal-based devices. However, the limited performance of green and blue light-emitting diodes (LEDs) based on CQWs has impeded their practical applications. In this study, alloy CdZnSe core CQWs with precise compositions are tailored via direct cation exchange (CE) from CdSe CQWs with specific size, shape, and crystal structure and utilized hot-injection shell (HIS) growth to synthesize CdZnSe/ZnS core/shell CQWs exhibiting exceptional optoelectronic characteristics. This approach enabled the successful fabrication green and blue LEDs manifesting superior performance compared to previously reported solution-processed CQW-LEDs. The devices demonstrated a remarkable peak external quantum efficiency (20.4% for green and 10.6% for blue), accompanied by a maximum brightness 347,683cd m-2 for green and 38,063cd m-2 for blue. The high-performance represents a significant advancement for nanocrystal-based light-emitting diodes (Nc-LEDs) incorporating anisotropic nanocrystals. This work provides a comprehensive synthesis strategy for enhancing the efficiency of Nc-LEDs utilizing anisotropic nanocrystals.

B(C6F5)3 Catalyzed Regiodivergent Thioetherifications of Alkenes via Thiiranium Intermediates: Experimental and Computational Insights.

Precise control of selective alkene functionalization is a continuing challenge in the chemical community. In this study, we develop a substitution-controlled regiodivergent thioetherification of di- or trisubstituted alkenes using 10 mol% tris(pentafluorophenyl)borane [B(C6F5)3] as a catalyst and N-thiosuccinimide as a sulfenylating reagent. This metal-free borane catalyzed C-S bond forming method is utilized for a Csp2-H sulfenylation reaction to synthesize an array of diphenylvinylsulfide derivatives with good to excellent yields (25 examples, up to 91% yield). Some of the products exhibit aggregation-induced emission luminogen properties used in organic light-emitting diodes (OLEDs), chemical sensors, and biological imaging units. Depending upon the starting alkene, Csp3-S sulfenylation products could also be generated regioselectively. A variety of allylic thioethers from α-alkyl substituted styrenes were isolable in good yields and selectivities (14 examples, up to 67% yield). The DFT-supported mechanistic study confirms that the reaction proceeds via a thiiranium ion intermediate, where the regioselectivity and product formation are determined by the alkene substituents which influences the activation barriers and energy profiles. Diphenylvinylsulfide derivatives can also be efficiently transformed into a range of synthetically valuable compounds, including vinyl sulfoxides, vinyl sulfones, and vinyl sulfoximines.

Improved Efficiency and Stability in Pure-Red CdSe Nanoplatelet LEDs Enabled by Gradient Alloyed CdSeS/CdZnS Crown/Shell.

Anisotropic nanoplatelets (NPLs) possess strong in-plane transition dipole moments and out-of-plane emission, which enable a maximum photon out-coupling efficiency of 40% and a high gain coefficient, making them ideal candidates for light-emitting diodes (LEDs) and lasers. However, the unbalanced surface energy between the side and top facets of NPLs results in poor thermal stability and high susceptibility to ripening at elevated temperatures, which complicates the growth of the shell. To address this issue, a gradient crown (CdSeS) around the CdSe NPLs is designed to stabilize the high energy side facets. Consequently, the gradient alloyed shell (CdZnS) is successfully grown, and the CdSe/CdSeS/CdZnS core/crown/shell NPLs exhibited near-unity photoluminescence quantum yield. The CdSeS/CdZnS crown/shell structure suppressed non-radiative Auger recombinations, achieving a record-low amplification spontaneous emission threshold of 2.11 µJcm-2 under femtosecond laser excitation. In addition, by selecting the carrier transport layers with matched energy levels, the NPL-LEDs demonstrate a record-high external quantum efficiency of 30.1% in the pure-red range, driven by the 94% in-plane transition dipole moment distribution of NPL film. The NPL-LEDs also exhibited a long operational lifetime of T95 > 600 h at a luminance of 1000 cdm-2.