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Quasi-two-dimensional (quasi-2D) perovskite has the advantage of enlarging exciton binding energy and is more suitable for efficient perovskite light-emitting diodes (PeLEDs). However, the quasi-2D perovskite films deposited with solution methods are usually mixtures of multiple phases with different inorganic layer numbers (n), unfavorable to obtaining high emission efficiency. In this study, we selected formamidinium lead bromide (FAPbBr3) as the light emitter and (2-phenylethyl)ammonium cation (PEA+) as the long-chain organic spacer cation to prepare high-n (n = 9) quasi-2D perovskite films with improved phase purity. Based on the multiple cations mixed engineering, the quality of these films improved obviously by partly replacing FA+ with minute quantities of cesium cation (Cs+). The improvement focused on remarkably enhanced photoluminescence, few low-n phases, and decreased grain sizes. The green PeLED based on the performance-optimized and phase purity-improved high-n quasi-2D perovskite reached a high brightness of 28 960 cd/m2 together with a maximum current efficiency of 44.8 cd/A and a maximum external quantum efficiency of 9.99%. [ABSTRACT FROM AUTHOR]

In this study, we establish comprehensive design guidelines to maximize single-mode transmission by efficient coupling between a III-nitride quantum-dot-in-nanowire light emitter and a photonic waveguide in the ultraviolet-visible (UV-Vis) spectral range. Considering feasible epitaxial growth, deposition, and fabrication techniques, this study performs detailed electromagnetic simulations to identify the design limits of viable material systems suitable for monolithic integration of vertical III-nitride nanowires on standard ridge waveguides. We show that unlike systems operating in the near-infrared wavelengths, light coupling and transmission in the UV-Vis range are significantly constrained by substrate leakage and backreflection. Such constraints arise from refractive index contrast of the associated waveguide and substrate materials suitable for epitaxial growth and device fabrication. For optimized dimensions of the nanowire and waveguide structures, the maximum unimodal transmission for practical monolithic systems is ∼ 14 % within the wavelength range of 300–500 nm. The theoretical transmission limit of the monolithic system is shown to be 35 % with a substrate of unity refractive index. It has been shown that the best strategy of maximizing coupling between the emission mode of the vertical nanowire and the propagation mode of the planar ridge waveguide is to increase the refractive index contrast between the waveguide and substrate material. Based on these key findings, we propose heterogeneously integrated hybrid structures, which significantly exceeds the unimodal transmission limits of standard monolithic systems attainable with III-nitride material systems in the UV-Vis wavelengths. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite CsPbBr3 nanocrystals (NCs) display high photoluminescence quantum yield and narrow emission, which show great potential application in optoelectronic devices. However, the poor environment stability of NCs will hinder their practical application. Herein, a series of ionic liquids with different anions (BF4−, Br−, and NO3−) were used as a sole capping ligand to synthesize NCs. Among the three samples, 1-hexadecyl-3-methylimidazolium tetrafluoroborate ([C16MIM]BF4) capped NCs have the highest stability in light, thermal, and water, possibly attributing to the in situ passivation of bromine vacancy via pseudohalogen BF4− and tight binding of ionic liquid ligands and lead atoms. In addition, green-emission [C16MIM]BF4 NCs were used to assemble a white light-emitting diode device, and it possessed a wide National Television System Committee color gamut of 124.5% and a stable emission peak at high driving currents of 380 mA. This work paves the way for resurfacing perovskite NCs with ultrahigh stability, thereby driving the perovskite NC display industry closer to real-world application. [ABSTRACT FROM AUTHOR]

Organic electronics (OE) such as organic light-emitting diodes or organic solar cells represent an important and innovative research area to achieve global goals like environmentally friendly energy production. To accelerate OE material discovery, various computational methods are employed. For the initial generation of structures, a molecular cluster approach is employed. Here, we present a semi-automated workflow for the generation of monolayers and aggregates using the GFNn-xTB methods and composite density functional theory (DFT-3c). Furthermore, we present the novel D11A8MERO dye interaction energy benchmark with high-level coupled cluster reference interaction energies for the assessment of efficient quantum chemical and force-field methods. GFN2-xTB performs similar to low-cost DFT, reaching DFT/mGGA accuracy at two orders of magnitude lower computational cost. As an example application, we investigate the influence of the dye aggregate size on the optical and electrical properties and show that at least four molecules in a cluster model are needed for a qualitatively reasonable description. [ABSTRACT FROM AUTHOR]

Integration of photonic crystal (PhC) configurations onto the surfaces of light-emitting diodes (LEDs) can play an important role in enhancing light extraction efficiency. While the literature is rich with various PhC fabrication approaches, there is a need for high throughput methods that are appropriate for low-cost devices. In this paper, we report the use of single pulse laser interference lithography (LIL) for the fabrication of photonic crystal structures on LEDs. The use of brief nanosecond pulse exposures offers significant benefits for high-throughput production. In our study, we have applied single pulse LIL on GaAs/AlGaAs LED structures to achieve high-quality photoresist arrays and then have used inductively coupled plasma etching to create nanoholes into the epitaxial structure. The resulting array forms an effective PhC, controlling surface transmission. Electroluminescence (EL) analyses confirm that these structures enhance the average EL intensity of the LED by up to 3.5 times at room temperature. This empirical evidence underscores the efficacy and potential of this fabrication approach in advancing the functional capabilities of semiconductor-based light-emitting devices. [ABSTRACT FROM AUTHOR]

The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermionic emission out of the QWs. In InGaN/GaN QWs, the thermionic hole transport is hindered by the high quantum confinement and polarization barriers. To overcome this drawback, hole injection through semipolar QWs located at sidewalls of V-defects had been proposed. However, in the case of the V-defect injection, strong lateral emission variations take place. In this work, we explore the nature of these variations and the impact of the V-defects on the emission spectra and carrier dynamics. The study was performed by mapping electroluminescence (EL) and photoluminescence (PL) with a scanning near-field optical microscope in LEDs that contain a deeper well that can only be populated by holes through the V-defects. Applying different excitation schemes (electrical injection and optical excitation in the far- and near-field), we have shown that the EL intensity variations are caused by the lateral nonuniformity of the hole injection. We have also found that, in biased structures, the PL intensity and decay time in the V-defect regions are only moderately lower that in the V-defect-free regions thus showing no evidence of an efficient Shockley-–Read–Hall recombination. In the V-defect regions, the emission spectra experience a red shift and increased broadening, which suggests an increase of the In content and well width in the polar QWs close to the V-defects. [ABSTRACT FROM AUTHOR]

Temperature-dependent piezoelectric-field characteristics of GaInN/GaN blue quantum wells are experimentally investigated between 100 and 300 K. The results show that the magnitude of the piezoelectric field increases with decreasing temperature with a slope of 1.08 kV cm−1 K−1 due to the increase in a mismatch between thermal expansion coefficients. To understand the impact of temperature-dependent piezoelectric field on the device performance, the external quantum efficiencies (EQEs) of a blue light-emitting diode are measured in the same temperature range. More severe EQE droops are observed at lower temperatures, which can be attributed to the increase in carrier overflow/spill-over to the p-clad layer enhanced by the stronger piezoelectric fields. The larger blueshifts in mean photon energy are simultaneously observed at lower temperatures, which also confirms the stronger piezoelectric fields at lower temperatures. [ABSTRACT FROM AUTHOR]

When combined with nanostructured substrates, two-dimensional semiconductors can be engineered with strain to tailor light–matter interactions on the nanoscale. Recently, room-temperature nanoscale exciton localization with controllable wrinkling in 1L-WSe2 was achieved using arrays of gold nanocones. Here, the characterization of quantum dot-like states and single-photon emitters in the 1L-WSe2/nanocone system is reported. The nanocones induce a wide range of strains, and as a result, a diverse ensemble of narrowband, potential single-photon emitters is observed. The distribution of emitter energies reveals that most reside in two spectrally isolated bands, leaving a less populated intermediate band that is spectrally isolated from the ensembles. The spectral isolation is advantageous for high-purity quantum light emitters, and anti-bunched emission from one of these states is confirmed up to 25 K. Although the spatial distribution of strain is expected to influence the orientation of the transition dipoles of the emitters, multimodal emission polarization anisotropy and atomic force microscopy reveal that the macroscopic orientation of the wrinkles is not a good predictor of dipole orientation. Finally, the emission is found to change with thermal cycling from 4 to 290 K and back to 4 K, highlighting the need to control factors such as temperature-induced strain to enhance the robustness of this quantum emitter platform. The initial characterization here shows that controlled nanowrinkles of 1L-WSe2 generate quantum light in addition to uncovering potential challenges that need to be addressed for their adoption into quantum photonic technologies. [ABSTRACT FROM AUTHOR]

When combined with nanostructured substrates, two-dimensional semiconductors can be engineered with strain to tailor light–matter interactions on the nanoscale. Recently, room-temperature nanoscale exciton localization with controllable wrinkling in 1L-WSe2 was achieved using arrays of gold nanocones. Here, the characterization of quantum dot-like states and single-photon emitters in the 1L-WSe2/nanocone system is reported. The nanocones induce a wide range of strains, and as a result, a diverse ensemble of narrowband, potential single-photon emitters is observed. The distribution of emitter energies reveals that most reside in two spectrally isolated bands, leaving a less populated intermediate band that is spectrally isolated from the ensembles. The spectral isolation is advantageous for high-purity quantum light emitters, and anti-bunched emission from one of these states is confirmed up to 25 K. Although the spatial distribution of strain is expected to influence the orientation of the transition dipoles of the emitters, multimodal emission polarization anisotropy and atomic force microscopy reveal that the macroscopic orientation of the wrinkles is not a good predictor of dipole orientation. Finally, the emission is found to change with thermal cycling from 4 to 290 K and back to 4 K, highlighting the need to control factors such as temperature-induced strain to enhance the robustness of this quantum emitter platform. The initial characterization here shows that controlled nanowrinkles of 1L-WSe2 generate quantum light in addition to uncovering potential challenges that need to be addressed for their adoption into quantum photonic technologies. [ABSTRACT FROM AUTHOR]

This study explores the effect of molecular permanent dipole moment (PDM) on aggregation of guest molecules in phosphorescent host–guest organic light-emitting diodes (OLEDs). Through a combination of photoluminescence measurements, high-angle annular dark-field scanning transmission electron microscopy analysis, and an Ising model based physical vapor-deposition simulation, we show that higher PDM of tris[2-phenylpyridinato-C2,N]iridium(III) guest can actually lead to a reduced aggregation relative to tris[bis[2-(2-pyridinyl-N)phenyl-C] (acetylacetonato)iridium(III) when doped into a non-polar host 1,3,5-tris(carbazol-9-yl)benzene. This study further explores the effect of host polarity by using a polar host 3′,5′-di(carbazol-9-yl)-[1,1′-biphenyl]-3,5-dicarbonitrile, and it is shown that the polar host leads to reduced guest aggregation. This study provides a comprehensive understanding of the impact of molecular PDM on OLED material efficiency and stability, providing insights for optimizing phosphorescent OLED materials. [ABSTRACT FROM AUTHOR]

In this study, we investigate the tradespace between the improvement of mid-infrared light-emitting diode efficiency through microcavity enhancement vs reduction of Auger recombination for different W-superlattice thicknesses. Several sample designs are modeled and then grown and fabricated to test the tradespace at different W-superlattice thicknesses down to the quantum well limit. In a half-cavity, with a single reflector from the top metal contact, intermediate thickness W-superlattices gave the highest efficiencies, outperforming those in the W-quantum well limit across the entire measured current range. Experimentally, we report wallplug efficiencies of 0.4% for a room temperature 3.2 μm device. W-superlattices of intermediate thickness were also found to be optimal for a full-cavity device with a bottom distributed Bragg reflector added. The resonant full cavity did strongly improve the peak spectral radiance, with a measured increase of four to five times for a 3.6 μm device, and a value that is >250 times larger than previously reported. [ABSTRACT FROM AUTHOR]

Recent years have seen an explosion of interest in organic radicals due to their promise for highly efficient organic light-emitting diodes and molecular qubits. However, accurately and inexpensively computing their electronic structure has been challenging, especially for excited states, due to the spin-contamination problem. Furthermore, while alternacy or "pseudoparity" rules have guided the interpretation and prediction of the excited states of closed-shell hydrocarbons since the 1950s, similar general rules for hydrocarbon radicals have not to our knowledge been found yet. In this article, we present solutions to both of these challenges. First, we combine the extended configuration interaction singles method with Pariser–Parr–Pople (PPP) theory to obtain a method that we call ExROPPP (Extended Restricted Open-shell PPP) theory. We find that ExROPPP computes spin-pure excited states of hydrocarbon radicals with comparable accuracy to experiment as high-level general multi-configurational quasi-degenerate perturbation theory calculations but at a computational cost that is at least two orders of magnitude lower. We then use ExROPPP to derive widely applicable rules for the spectra of alternant hydrocarbon radicals, which are completely consistent with our computed results. These findings pave the way for highly accurate and efficient computation and prediction of the excited states of organic radicals. [ABSTRACT FROM AUTHOR]

Nonvolatile memory using intersubband transitions and quantum-well electron accumulation in GaN/AlN resonant tunneling diodes (RTDs) is a promising candidate for high-speed nonvolatile memory operating on a picosecond timescale. This memory has been fabricated on sapphire(0001) substrates to date because of the high affinity between the nitride materials and the substrate. However, the fabrication of this memory on Si(111) substrates is attractive to realize hybrid integration with Si devices and nonvolatile memory and three-dimensional integration such as chip-on-wafer and wafer-on-wafer. In this study, GaN/AlN RTDs are fabricated on a Si(111) substrate using metal-organic vapor phase epitaxy. The large strain caused by the differences in the thermal expansion coefficients and lattice constants between the Si(111) substrate and nitride materials are suppressed by a growth technique based on the insertion of low-temperature-grown AlGaN and thin AlN layers. The GaN/AlN RTDs fabricated on Si(111) substrates show clear GaN/AlN heterointerfaces and a high ON/OFF ratio of >220, which are equivalent to those for devices fabricated on sapphire(0001) substrates. However, the nonvolatile memory characteristics fluctuate by repeated write/erase memory operations. Evaluation of the ON/OFF switching time and endurance characteristics indicates that the instability of the nonvolatile memory characteristics is caused by electron leakage through deep levels in the quantum-well structure. Possible methods for suppressing this are discussed with an aim of realizing high-speed and high-endurance nonvolatile memory. [ABSTRACT FROM AUTHOR]

Charge carrier mobility and recombination determine the performance of many opto-electronic devices such as solar cells, sensors, and light-emitting diodes. Understanding how these parameters change as a function of material choice, charge carrier density, and device geometry is essential for developing the next generation of devices. The time-delayed collection field (TDCF) technique is becoming a widely used method to measure both recombination and carrier transport with values derived from this method being widely reported for many material systems. However, most novel materials are highly disordered with a high density of trap states and standard TDCF theory neglects the influence of these states. In this work, we examine how reliable TDCF can be as a measurement technique when the device contains significant energetic disorder. We identify regimes where the results can be relied upon and where the results should be taken with more caution. Finally, we provide simple and easy to use experimental tests to help the experimentalist decide whether the physical processes are dominated by trap states. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbene (NHC) iridium(III) complexes are considered as promising candidates for blue emitters in organic light-emitting diodes. They can play the roles of the emitter as well as of electron and hole transporters in the same emission layer. We investigate optical transitions in such complexes with account of geometry and electronic structure changes upon excitation or charging and exciton transfer between the complexes from first principles. It is shown that excitation of NHC iridium complexes is accompanied by a large reorganization energy ∼0.7 eV and a significant loss in the oscillator strength, which should lead to low exciton diffusion. Calculations with account of spin–orbit coupling reveal a small singlet–triplet splitting ∼0.1 eV, whereas the oscillator strength for triplet excitations is found to be an order of magnitude smaller than for the singlet ones. The contributions of the Förster and Dexter mechanisms are analyzed via the explicit integration of transition densities. It is shown that for typical distances between emitter complexes in the emission layer, the contribution of the Dexter mechanism should be negligible compared to the Förster mechanism. At the same time, the ideal dipole approximation, although giving the correct order of the exciton coupling, fails to reproduce the result taking into account spatial distribution of the transition density. For charged NHC complexes, we find a number of optical transitions close to the emission peak of the blue emitter with high exciton transfer rates that can be responsible for exciton–polaron quenching. The nature of these transitions is analyzed. [ABSTRACT FROM AUTHOR]

Laser lift-off (LLO) is an important step in the processing chain of nitride-based light-emitting diodes (LEDs), as it enables the transfer of LEDs from the growth substrate to a more suitable carrier. A distinctive feature of LLO with ultrashort pulses is the ability to use either above- or below-bandgap radiation, since nonlinear absorption becomes relevant for ultrashort pulses. This study addresses the differences in the absorption scheme for below- and above-bandgap radiation and investigates the electrical and optical properties of InGaN/GaN LEDs before and after LLO with 347 and 520 nm laser light via current–voltage and power- as well as temperature-dependent photoluminescence measurements. LLO could be successfully realized with both wavelengths. The threshold fluence required for LLO is about a factor of two larger for 520 nm compared to that for 347 nm. Furthermore, an increase in leakage current by several orders of magnitude and a significant decrease in efficiency with laser fluence are observed for below-bandgap radiation. In contrast, leakage current hardly increases and efficiency is less dependent on the laser fluence for samples lifted with 347 nm. This degradation is ascribed to the absorption of laser light in the active region, which facilitates a modification of the local defect landscape. The effect is more severe for below-bandgap radiation, as more laser light penetrates deep into the structure and reaches the active region. Ultimately, we show that LEDs lifted with ultrashort laser pulses can exhibit good quality, making ultrashort pulse LLO a viable alternative to conventional LLO with nanosecond pulses. [ABSTRACT FROM AUTHOR]

Limited stability of blue quantum dot light-emitting diodes (QLEDs) under current stress impedes commercialization. Multi-layer structures of the state-of-the-art blue QLEDs pose significant difficulty in the fundamental understanding of degradation mechanisms. Here, by applying transient electroluminescence measurements, we disentangle charge transport in both pristine and degraded blue QLEDs. By varying thicknesses of the charge transport layers and the emissive layer, respectively, we show that the charge transport in pristine QLEDs is primarily dominated by holes. Furthermore, the degradation of QLEDs under electrical stress is governed by the decrease of hole transport in the emissive quantum dot layer due to the formation of hole traps. [ABSTRACT FROM AUTHOR]

We introduce a multiple-carrier-lifetime model (MCLM) for light-emitting diodes (LEDs) with non-uniform carrier distribution, such as in multiple-quantum-well (MQW) structures. By employing the MCLM, we successfully explain the modulation response of V-pit engineered MQW LEDs, which exhibit an S21 roll-off slower than −20 dB/decade. Using the proposed model and employing a gradient descent method, we extract effective recombination and escape lifetimes by averaging the carrier behavior across the quantum wells. Our results reveal slower effective carrier recombination and escape in MQW LEDs compared with LEDs emitting from a single QW, indicating the advantages of lower carrier density achieved through V-pit engineering. Notably, the effective carrier recombination time is more than one order of magnitude lower than the effective escape lifetime, suggesting that most carriers in the quantum wells recombine, while the escape process remains weak. To ensure the reliability and robustness of the MCLM, we subject it to a comprehensive threefold validation process. This work confirms the positive impact of spreading carriers into several quantum wells through V-pit engineering. In addition, the MCLM is applicable to other LEDs with a non-uniform carrier distribution, such as micro-LEDs with significant surface recombination and non-uniform lateral carrier profiles. [ABSTRACT FROM AUTHOR]

The effect of inserting a nm-scale layer of Zn(Si,Ge)N2 into an AlGaN quantum well structure designed for light emission in the wavelength range from 255 to 305 nm is investigated here. The enhanced confinement of the hole within the quantum well results in an enhancement of the overlap of the hole and electron wave functions, resulting in an enhancement of the radiative recombination rate. In this theoretical calculation, for emission at a 270 nm wavelength, the enhancement in the wavefunction overlap can reach a factor of 7 when compared to an AlGaN quantum well device specifically engineered for optimal emission at the identical wavelength. Increases of almost an order of magnitude in both the peak spontaneous emission intensity and the radiative recombination rate are predicted. The peak emission wavelength can be tuned from 255 to 305 nm by adjusting the width and/or the composition of the inserted layer. The proposed structures provide a route to higher efficiency ultraviolet practical light emitting diodes and lasers. [ABSTRACT FROM AUTHOR]

The polarization-induced quantum confined Stark effect has been recognized as a significant factor contributing to the Internal Quantum Efficiency (IQE) droop in light-emitting diodes (LEDs). This study focuses on the design of LEDs by investigating the InAlN/AlGaN interface. By incorporating InAlN quantum wells, a polarization-matched (PM) multi-quantum well (MQW) LED architecture was developed. While the flat conduction and valence bands on PM MQWs indicate an improved recombination rate, it is crucial to examine the impact on IQE, considering carrier confinement and injection efficiency influenced by the band offsets. This paper presents a numerical analysis comparing two LEDs emitting at 245 and 275 nm, respectively. The results demonstrate that the PM LED operating at 275 nm exhibits enhanced performance, benefiting from high probability density overlap. Conversely, the PM LED emitting at 245 nm demonstrates poor confinement, resulting in an overall low performance, regardless of polarization matching. [ABSTRACT FROM AUTHOR]

We found that varying the degree of conjugation in achiral LC polymers can lead to tunable CPL/CP-EL behaviors of the resulting co-assemblies during the chiral co-assembly process. Notably, chiral co-assemblies (R / S -FO) 0.1 -(PFNa) 0.9 emitted the strongest CPL signals after thermal annealing treatment due to the formation of the stable helical nanofibers. The CP-OLEDs based on EMLs of (R / S -FO) 0.1 -(PFNa) 0.9 demonstrated the best CP-EL performance (| g EL | = 0.014, L max = 3039 cd m−2, CE max = 1.16cd/A). [Display omitted] • The chiral co-assemblies were constructed and exhibited tunable CPL/CP-EL behaviors. • The effect of conjugated groups on co-assembly was investigated at the molecular level. • The same naphthyl moieties can lead to optimal compatibility and the strongest CPL signals. • The largest g EL value of CP-OLEDs based on chiral co-assemblies can up to 0.014. Chiral co-assembly strategy has proven effective in increasing the dissymmetry factor (g EL) of the emitting layers (EMLs) in circularly polarized organic light-emitting diodes (CP-OLEDs). Therefore, it is crucial to investigate the molecular structures that facilitate chiral co-assembly for further amplification of circularly polarized electroluminescence (CP-EL) signals. In this study, three types of achiral conjugated liquid crystal (LC) polymers (PFPh , PFNa and PFPy) and chiral binaphthyl-based polymer inducers ( R / S -FO) were synthesized to construct corresponding chiral co-assemblies (R / S -FO) 0.1 -(PFPh/Na/Py) 0.9 as EMLs for CP-OLEDs through strong intermolecular π – π stacking interactions. Interestingly, these resulting chiral co-assembled EMLs exhibited tunable CP-EL behaviors caused by the different conjugation linkers of LC polymers. Among them, the deep blue devices based on (R / S -FO) 0.1 -(PFNa) 0.9 emitted the strongest CP-EL signals (| g EL | = 0.014, L max = 3039 cd m−2, CE max = 1.16 cd A−1). It is attributed to the formation of ordered helical nanofibers facilitated by the excellent intermolecular compatibility due to the same naphthyl moieties in PFNa and R / S -FO. This study provides novel perspectives for developing high-performance CP-EL materials in chiral co-assembly systems. [ABSTRACT FROM AUTHOR]

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 GeO 2 and SnO 2 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). [ABSTRACT FROM AUTHOR]

This study investigated the disinfection efficiency of a photoreactor equipped with a helical water flow channel and ultraviolet-C (UV-C) light emitting diodes (LEDs). Theoretical simulations and biodosimetry tests were conducted to investigate the effects of coil diameter and flow rate on the reactor's performance in inactivating Escherichia coli. The interplay between hydrodynamics and UV radiation was analyzed to determine the UV fluence absorbed by the microbes. The simulations revealed that, primarily due to the specific radiation pattern of the UV LEDs, the coil diameter strongly influenced the distribution of irradiance in the water and the UV fluence received by microbes. The experimental results indicated that the photoreactor achieved the highest inactivation value of 2.8 log when the coil diameter was 48 mm for a flow rate of 40 mL/min; this log value was superior to those for coil diameters of 16, 32, 64, and 80 mm by approximately 1.9, 0.4, 0.5, and 0.7 log units, respectively. This optimal coil diameter leading to the maximal UV irradiance and the highest degree of irradiance uniformity along the flow channel. This study offers design guidelines for constructing a high-efficiency water disinfection reactor with a helical flow channel configuration. [ABSTRACT FROM AUTHOR]

A novel functionalization approach of quinoxaline has been unveiled to develop orange/red thermally activated delayed fluorescence (TADF) emitters by modifying the core with three carbazole donors and one or three cyano acceptors. The resulting functionalized TADF emitters demonstrated orange and red emission with promising TADF properties. An organic light-emitting diode fabricated using the orange emitter demonstrated high external quantum efficiency of 18.4%. [ABSTRACT FROM AUTHOR]

Stable silicone encapsulants are essential for protecting high‐power light‐emitting diodes (LED) from dust and moisture and extending their service life. Herein, by incorporating thiol‐functionalized polyhedral oligomeric silsesquioxane (SH‐POSS) as a crosslinker into ultraviolet‐curable silicone elastomer (UVSE), a series of new UV‐cured silicone encapsulants (SH‐POSS/UVSE) have been developed through thiol‐ene click chemistry. It was found that SH‐POSS effectively enhanced the mechanical properties of SH‐POSS/UVSE. When 30 mol% SH‐POSS was added, the tensile strength and elongation at break reached 1.01 MPa and 422%, respectively, 2.1 and 1.6 times higher than pure UVSE. This could be ascribed to the more concentrated crosslinking network and the improved interfacial interactions between SH‐POSS and UVSE than physical blending. Moreover, the steric effect of branched and rigid SH‐POSS restricted the movement of UVSE molecular chains. Incorporating SH‐POSS also suppressed UVSE degradation and improved its thermal stability. Additionally, when the LED sample encapsulated by SH‐POSS/UVSE‐30 was immersed in boiling red ink for 2 h, no crack or stain was observed, indicating that SH‐POSS/UVSE‐30 possessed good adhesion to the LED lead frame. This work provides a new approach to fabricating high‐strength and stable silicone composites, which are promising candidates as LED encapsulants. [ABSTRACT FROM AUTHOR]

The development of novel, efficient and cost-effective emitters for solid-state lighting devices (SSLDs) is ubiquitous to meet the increasingly demanding needs of advanced lighting technologies. In this context, the emergence of thermally activated delayed fluorescence (TADF) materials has stunned the photonics community. In particular, inorganic TADF material-based compounds can be ad hoc engineered by chemical modification of the coordinated ligands and the type of metal centre, allowing control of their ultimate photo-/electroluminescence properties, while providing a viable emitter platform for enhancing the efficiency of state-of-the-art organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs). By presenting an overview of the state of the art of all metal complex-based TADF compounds, this review aims to provide a comprehensive, authoritative and critical reference for their design, characterization and device application, highlighting the advantages and drawbacks for the chemical, photonic and optoelectronic communities involved in this interdisciplinary research field. [ABSTRACT FROM AUTHOR]

Zero-dimensional (0D) chiral hybrid metal halides (HMHs) with narrow-band circularly polarized luminescence (CPL) show considerable promise in three-dimensional displays. In this work, 0D (S/R-3MOR)3TbCl6 and (S/R-3MOR)3EuCl6 (abbreviated as S/R-TbCl, S/R-EuCl) enantiomers with characteristic rare-earth ion emissions are synthesized. S/R-TbCl and S/R-EuCl exhibit narrow-band green and red emissions with high photoluminescence quantum yields of (85–91)% and (48–52)%, respectively. These materials present distinct CPL signals with dissymmetry factors up to ±0.006 and ±0.009 for S/R-TbCl and S/R-EuCl, respectively. These chiroptical properties confer the potential for their applications in circularly polarized light-emitting diodes for future displays. [ABSTRACT FROM AUTHOR]

Constructing folded molecular structures is emerging as a promising strategy to develop efficient thermally activated delayed fluorescence (TADF) materials. Most folded TADF materials have V‐shaped configurations formed by donors and acceptors linked on carbazole or fluorene bridges. In this work, a facile molecular design strategy is proposed for exploring sandwich‐structured molecules, and a series of novel and robust TADF materials with regular U‐shaped sandwich conformations are constructed by using 11,12‐dihydroindolo[2,3‐a]carbazole as bridge, xanthone as acceptor, and dibenzothiophene, dibenzofuran, 9‐phenylcarbazole and indolo[3,2,1‐JK]carbazole as donors. They hold outstanding thermal stability with ultrahigh decomposition temperatures (556–563 °C), and exhibit fast delayed fluorescence and excellent photoluminescence quantum efficiencies (86 %–97 %). The regular and close stacking of acceptor and donors results in rigidified molecular structures with efficient through‐space interaction, which are conducive to suppressing intramolecular motion and reducing reorganized excited‐state energy. The organic light‐emitting diodes (OLEDs) using them as emitters exhibit excellent electroluminescence performances, with maximum external quantum efficiencies of up to 30.6 %, which is a leading value for the OLEDs based on folded TADF emitters. These results demonstrate the proposed strategy of employing 11,12‐dihydroindolo[2,3‐a]carbazole as bridge for planar donors and acceptors to construct efficient folded TADF materials is applicable. [ABSTRACT FROM AUTHOR]

Quasi‐two‐dimensional (Q‐2D) Ruddlesden‐Popper (RP) perovskites are rapidly developed for photoelectric device applications due to their unique multiple quantum‐well structures and adjustable photoelectric properties. Here, a three‐in‐one multifunctional photoelectric device that integrates photovoltaic (PV), electroluminescence (EL), and photodetection performance based on Q‐2D perovskite, which has not yet been reported, is explored and realized. As a solar cell (SC) mode under standard air mass 1.5G illumination, the optimal device has a power conversion efficiency (PCE) of 10.36%; as a light emitting diode (LED) mode under forward bias, the optimal device emits red light at 753 nm and achieves an EL external quantum efficiency (EQEEL) of 0.42%; as a photodetector (PD) mode under a pulsed laser (660 nm), the optimal device exhibits superior weak‐light detection, with a linear dynamic range (LDR) improvement as wide as 161.8 dB, a high detectivity (D*) of 7.88 × 1012 Jones, a fast rise/fall time of 19.1/35.2 µs and excellent stability. This work is of great significance to enrich the physical connotation and comprehensively improve the use efficiency of the multifunctional device. [ABSTRACT FROM AUTHOR]

Wide color gamut and high resolution are becoming key features of the new generation of displays, and hence quantum dots pixels with high luminescence purity have been placed great expectations. However, how to facilely and rapidly fabricate electroluminescent pixels with both high pixels per inch (PPI) and high quantum efficiency has been a great challenge. Here, a one‐step, mask‐free, rapid laser writing strategy to fabricate ultra‐high resolution perovskite quantum dots (PQDs) pixels is presented. It is found that the laser‐induced reaction can convert PQDs into oxide, forming perovskite@oxide pixel arrays, replacing the complex etching and deposition processes previously used. Benefiting from the formation of the oxide layer, electrons transport can be effectively blocked in the non‐emitting region, thus reducing the charge leakage in micro quantum dots light emitting diodes (Micro‐QLED) arrays. Finally, red, green, blue Micro‐QLEDs are achieved with PPIs ranging from 2000 to 5000 and the highest external quantum efficiency of 17.24%, 21%, and 6.6% respectively. These results are record‐breaking in perovskite Micro‐QLEDs, providing the strategy for active‐matrix electroluminescent high‐resolution pixel arrays for next‐generation monochromatic displays. [ABSTRACT FROM AUTHOR]

High-performance phosphors are essential for phosphor-converted white light-emitting diodes (pc-LEDs) utilized in general lighting applications. This paper introduces Eu2+-activated nepheline solid-solution yellow phosphors Na 2.95+ x K 1- x (AlSiO 4) 4 :0.05Eu2+ exhibiting excellent luminescent properties. All samples demonstrate an emission band at approximately 530 nm. However, the emission intensity gradually increases with higher Na+ content, progressing from Na 2.95 K(AlSiO 4) 4 :0.05Eu2+ to Na 3.95 (AlSiO 4) 4 :0.05Eu2+. Correspondingly, the external quantum efficiency (EQE) significantly rises from 41 % to 60 %. This enhancement in EQE is attribute to the improved absorption efficiency resulting from increased crystallinity. Notably, the emission intensity of representative phosphors at 150 °C remains above 90 % of room temperature values, indicating excellent thermal stability. A white pc-LED with a color-rendering index exceeding 85 is successfully developed using the phosphor with the highest EQE. These findings indicate that Na 2.95+ x K 1- x (AlSiO 4) 4 :0.05Eu2+ phosphors show promise as potential candidates for pc-LEDs in general lighting applications. [ABSTRACT FROM AUTHOR]

Fully π-conjugated polymers consisting of plane and rigid aromatic units present a fantastic optoelectronic property, a promising candidate for printed and flexible optoelectronic devices. However, obtaining high-performance conjugated polymers with an excellent intrinsically flexible and printable capacity is a great challenge due to their inherent coffee-ring effect and brittle properties. Here, we report an asymmetric substitution strategy to improve the printable and stretchable properties of deep-blue light-emitting conjugated polymers with a strong inter-aggregate capillary interaction for flexible printed polymer light-emitting diodes. The loose rod-shaped stacking of asymmetric conjugated polymers chain in the precursor printed ink makes it easier to improve the intrinsic stretchability of inkjet-printed films. More interestingly, the anisotropic shape rod-like aggregate of conjugated polymers chains also induced a strong capillary interaction and further suppressed the coffee-ring effect, which is more likely to allow for uniform deposition during printed processing and form uniform printed films. Achieving high-performance conjugated polymers with intrinsic flexibility and printable capacity is a great challenge. Here, the authors report asymmetric substituted polymers with strong inter aggregate capillary interaction for deep-blue flexible printed polymer light-emitting diodes. [ABSTRACT FROM AUTHOR]

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The bioluminescent European brittle star Amphiura filiformis produces blue light at the arm-spine level thanks to a biochemical reaction involving coelenterazine as substrate and a Renilla-like luciferase as an enzyme. This echinoderm light production depends on a trophic acquisition of the coelenterazine substrate. Without an exogenous supply of coelenterazine, this species loses its luminous capabilities. Moreover, this species was recently shown not to produce coelenterazine storage forms. As an infaunal suspensive feeder, A. filiformis is assumed to find enough substrate to maintain its bioluminescence capabilities efficiently. To date, no studies have investigated the putative source of coelenterazine in the brittle star diet. A combined analysis using listing based on visual observations and metabarcoding on the planktonic communities highlights planktonic species known as light emitters using coelenterazine. Besides, the A. filiformis stomach content was analyzed seasonally via metabarcoding technique, and coelenterazine-related preys were underlined. Results provide evidence of the presence of preys containing coelenterazine in the fjord environment and within the stomach content of the ophiuroid throughout the year. The results are consistent with the demonstration of the trophic acquisition of luminous capabilities in A. filiformis and give a new step by underlying the constant presence of coelenterazine suppliers throughout the year for the luminescence reaction occurring within this species. [ABSTRACT FROM AUTHOR]

In the past decades, benefitting from the development of synthesis methodology, Cd‐based semiconductor nanocrystals (NCs) have been extensively studied and their structure‐dependent properties further inspired diverse applications. However, the high toxicity of Cd in Cd‐based semiconductor NCs significantly limits their widespread applications. Colloidal Zn‐based semiconductor NCs are one of the most promising candidates for Cd‐based semiconductor NCs attributed to their low toxicity, creating high‐band gap systems with excellent optoelectronic properties. Herein, an overview of the synthesis, structure engineering, and optoelectronic applications of colloidal Zn‐based semiconductor NCs are provided. In the first section, the typical growth mechanisms are introduced, including oriented attachment, templated‐assisted growth, and ripening. Then, structure engineering, such as core–shell structure, heterostructure, alloying, and doping, of Zn‐based NCs are summarized. Simultaneously, an insight into various applications related to these structures of Zn‐based NCs are given, including quantum dots light emitting diodes (QLEDs), catalysts, biological‐application, sensors, and solar cells. Finally, although huge progress in both synthesis methodology and applications of colloidal Zn‐based semiconductor NCs have been achieved, some issues still hinder the further development of Zn‐based semiconductor NCs. Then in the last section, it is elaborated on the challenges and provides the possible solutions to tackle these challenges. [ABSTRACT FROM AUTHOR]

Light-emitting diode (LED) lamps are efficient elicitors of secondary metabolites. To investigate the influence of LED light on steviol glycosides (SGs) and phenolic compounds biosynthesis, stevia shoots were cultured under the following LED lights: white–WL, blue–B, red–R, 70% red and 30% blue–RB, 50% UV, 35% red and 15% blue–RBUV, 50% green, 35% red and 15% blue–RBG, 50% yellow, 35% red and 15% blue–RBY, 50% far-red, 35% red and 15% blue–RBFR and white fluorescent light (WFl, control). RBG light stimulated shoots' biomass production. RBFR had a beneficial impact on stevioside biosynthesis (1.62 mg/g dry weight, DW), while RBUV favoured the production of rebaudioside A (3.15 mg/g DW). Neochlorogenic, chlorogenic, caffeic, 4-feruloylquinic, isochlorogenic A, rosmarinic acids and the flavonoid quercitrin were identified in the obtained material. A stimulatory effect of RBFR and RBUV on the biosynthesis of phenolic compounds was noted. LED light also influenced stomata appearance, stomata density, photosynthetic pigments, soluble sugar content and antioxidant enzyme activities in stevia shoots. This is the first report to provide evidence of the stimulating effect of LED light on biomass yield, SGs production and phenolic compounds in stevia shoot cultures. [ABSTRACT FROM AUTHOR]

Metal halide perovskites show promise for next-generation light-emitting diodes, particularly in the near-infrared range, where they outperform organic and quantum-dot counterparts. However, they still fall short of costly III-V semiconductor devices, which achieve external quantum efficiencies above 30% with high brightness. Among several factors, controlling grain growth and nanoscale morphology is crucial for further enhancing device performance. This study presents a grain engineering methodology that combines solvent engineering and heterostructure construction to improve light outcoupling efficiency and defect passivation. Solvent engineering enables precise control over grain size and distribution, increasing light outcoupling to ~40%. Constructing 2D/3D heterostructures with a conjugated cation reduces defect densities and accelerates radiative recombination. The resulting near-infrared perovskite light-emitting diodes achieve a peak external quantum efficiency of 31.4% and demonstrate a maximum brightness of 929 W sr−1 m−2. These findings indicate that perovskite light-emitting diodes have potential as cost-effective, high-performance near-infrared light sources for practical applications. Baek et al. report the formation of a discrete island–convex dome morphology in perovskite by solvent engineering to improve the outcoupling efficiency in NIR LEDs. 2D/3D heterostructures are constructed to further increase the efficiency to 31.4% with a peak radiance of 929 W sr−1 m−2 at 798 nm. [ABSTRACT FROM AUTHOR]

Excited‐state intramolecular proton transfer (ESIPT) molecules are promising fluorophores for various applications including bioimaging, sensing, and optoelectronic devices. Particularly, their self‐absorption‐free fluorescence properties would make them a perfect choice as emissive materials for organic light‐emitting diodes (OLEDs). Nevertheless, to become effective emitters some of their properties need to be altered by structural modifications. Herein, we design and synthesize a series of new ESIPT molecules (2PImBzP, 2ImBzP, and 2FImBzP) by functionalization of imidazole‐phenol‐based ESIPT cores with electron‐deficient benzo[d]thiazole and various ambipolar imidazole moieties (1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (PIm), 1,4,5‐triphenyl‐1H‐imidazole (Im), and (4,5‐bis(4‐fluorophenyl)‐1‐phenyl‐1H‐imidazole (FIm)), respectively. Each molecule displays a complete ESIPT process with intense green emissions from a pure keto form and high solid‐state photoluminescence quantum yields (ΦPL) of 65–80 %. These fluorophores with superior thermal stability and balanced charge carrier mobility are effectively employed as non‐doped emitters in OLEDs. The non‐doped devices emit greenish lights with high brightness, high current efficiency (CE) (10.95–17.66 cd A−1), and low turn‐on voltages (2.8–2.9 V). The electroluminescence purely originates from the emission of the keto tautomer of the emissive layers. Specifically, the 2PImBzP‐based non‐doped OLED stands out by achieving a remarkable brightness of 56,220 cd m−2, a CE of up to 17.66 cd A−1, and an impressive external quantum efficiency (EQE) of 5.65 % with a slight efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Modern application trends for the development of RGB displays with a high color rendering index (CRI) require light-emitting diode (LED) display technology with greater miniaturization and efficient LEDs operating at deep red wavelengths greater than 650 nm. Although InGaN-based LEDs have achieved high miniaturization performance, efforts to obtain deep-red emission by increasing the indium content introduce a number of factors limiting optical performance, such as high in-plane stress, high dislocation densities, and phase separation. The present work addresses this issue by fabricating deep-red emitting InGaN-based LEDs on an underlying GaN template layer grown from hexagonal GaN column structures formed on a porous SiNx masking layer and coalesced in situ as an underlying layer with significantly reduced internal stresses and dislocation densities. As a result, the fabricated miniature LEDs obtain an external quantum efficiency of 9.1% and a peak wavelength of 672 nm at a current density of 0.4 A/cm2. Accordingly, this work confirms the potential for fabricating InGaN-based LEDs to achieve high-CRI mini/micro RGB displays. [ABSTRACT FROM AUTHOR]

The island‐bridge structural design is a common strategy for imparting stretchability to flexible electronic devices. In this structure, the low modulus regions bear most of the deformation, while the rigid islands, which house the electronic components, undergo minimal deformation. However, due to the modulus differences that can be several times or even several orders of magnitude larger, severe strain concentration occur at the edges of the rigid islands in high modulus regions. This strain concentration caused by rigid constraints not only reduces the stretchability of the soft substrate but also degrades the mechanical performance of the interconnected structures, thereby significantly affecting the overall stability of the device. Starting from finite element simulations, this paper introduces modulus gradient regions and optimizes geometric parameters, significantly alleviating the strain concentration at the edges of the rigid islands. Serpentine‐shaped circuits are then transferred to a substrate with strain isolation, which demonstrates better stretchability stability under 20% elongation compared to traditional strain isolation strategies. In addition, the stretchable light emitting diode (LED) system with gradient modulus has better stretchability compared to the system with conventional strategy. This suggests that this strategy has great potential in maintaining the stability of stretchable systems. [ABSTRACT FROM AUTHOR]

The nonconventional polymer luminophores (NPLs) with white emission are scarce due to the challenges in regulating their clustering structures. In this work, polystyrene is employed to develop a new kind of broad‐emitting clusteroluminescence (CL) through suitable cross‐linking and sulfonation. The sulfonated porous poly(styrene‐co‐divinylbenzene) microspheres (SPDMs) exhibit broad emission spectra (400–700 nm) in the visible light region. Further characterization and theoretical calculations show that through‐space conjugation (TSC) enhanced with high cross‐linking and sulfonation degrees (SD) is the main factor affecting the luminescence of microspheres. Monodisperse SPDMs with a low fluorescence distribution (CV < 5%) across 13 flow channels. Additionally, SPDMs microspheres is employed to construct binary, Cu2+, and pH‐responsive microarrays to encrypt and decode important information. Finally, SPDMs are developed for utilization as single‐component white and warm white light‐converting light emitting diodes (LEDs). These LEDs demonstrate Commission International de L'Eclairage (CIE) coordinates and correlate color temperatures (CCT) of (0.31, 0.321) and (0.383, 0.41), 6611 and 4100 K, respectively. Notably, the color rendering index (CRI) value for SPDMs‐50‐2 in white LED applications reaches an impressive 92. This study provides an economical, simple, and effective design strategy for developing NPLs with both monodispersity and broad emission. [ABSTRACT FROM AUTHOR]

Helicenes and helicenoid structures are promising candidates for future applications exploiting circularly polarized light. Ideal candidates should possess near‐quantitative photoluminescence quantum yield, a high luminescence dissymmetry factor and an adjustable HOMO‐LUMO gap. However, carbo[n]helicenes are poorly luminescent compounds and they absorb light mainly in the ultraviolet region. Here we show that the incorporation of a carbonyl group into helical scaffold significantly improves the fluorescence quantum yield and shifts the absorption to visible region. Although the carbonyl group is commonly considered as detrimental to efficient emission, fluorescence quantum yields up to Φ=0.43 were recorded. A straightforward synthetic approach to a highly luminescent tetraceno[6]helicenone and an aza analogue has been developed. The key step is a radical cyclization which is achieving dehydrative π‐extension. The aza‐analogue was incorporated as an emitter in organic light emitting diodes (OLEDs) and showed good performance. [ABSTRACT FROM AUTHOR]

Charge imbalance in inverted InP‐based quantum dot light emitting diodes (QLEDs) due to higher electron injection is a well‐known hindrance to the device's stability. To overcome this, the exciton harvesting layer (EHL) is inserted between QD and the hole transport layer to recycle overflowing electrons, form excitons, and transfer exciton energies to QD layer. This study utilized exciplex as EHL in InP‐based QLEDs. The exciplex EHL is composed of 2‐(5‐(dibenzo[b,d]furan‐4‐yl)‐[1,1′‐biphenyl]‐3‐yl)‐4‐phenyl‐6‐(8‐phenyldibenzo[b,d]furan‐1‐yl)‐1,3,5‐triazine (diDBFTrz) as n‐type and ([1,1′‐biphenyl]‐4‐yl).‐9′‐phenyl‐9H,9′H‐3,3′‐bicarbazole (BPP‐BCZ) as p‐type material. The exciplex is chosen based on its compatibility with QD, which mitigates issues in QLEDs. Through the optimization of the exciplex layer, the maximum external quantum efficiency (EQE) is enhanced from 10.9% to 19.2%. The BPP‐BCZ: diDBFTrz exciplex ratio of 6:4 (max EQE: 17.3%) achieves the calculated half‐operation lifetime of 1881 h at 1000 cd m−2. The findings pave the way for using exciplex as EHL in QLEDs to increase the device's operational lifetime and efficiency. [ABSTRACT FROM AUTHOR]

The effect of bulk AlN single‐crystal substrate thickness on the light extraction efficiency and external quantum efficiency of far ultraviolet‐C light emitting diodes (far‐UVC LEDs) has been investigated. AlGaN multi‐quantum well LEDs designed for emission around 235 nm are grown by metal organic vapor phase epitaxy on low defect density bulk AlN substrates as well as on AlN/sapphire templates. As the AlN substrate is thinned step‐by‐step from 550 to 70 μm by chemo‐mechanical polishing, the output power of LEDs increased from 3 μW for a thickness of 550 to 110 μW for a thickness of 70 μm (on‐wafer at a dc current of 100 mA). From the Lambert–Beer law an effective absorption coefficient of (84 ± 4) cm−1 is derived for the AlN substrate. Monte Carlo ray‐tracing simulations for an AlN substrate thickness of 70 μm yield an on‐wafer LEE of (0.9 ± 0.1)% and the internal quantum efficiency was estimated to be (5.6 ± 1.5)%. [ABSTRACT FROM AUTHOR]