Application In Light-emitting Diodes Research Articles

2D/3D perovskite heterojunctions: Composition and application in light-emitting diodes

2D/3D perovskite heterojunctions: Composition and application in light-emitting diodes

The impact of antimony on all-inorganic lead-free perovskites: progress in optical advancement and applications.

The incorporation of Sb3+ ions into all-inorganic halide lead-free perovskites bestows them with remarkable photoluminescence characteristics, including an extensive color tuning range, elevated photoluminescence quantum yield (PLQY), and reversible color transitions, which hold significant promise for applications in light-emitting diodes, anti-counterfeiting encryption technologies, and photodetectors. Sb3+ ions not only create new optical absorption channels but also can be integrated into these materials as activators or sensitizers to modulate the bandgap and band structure. This review focuses on the optical properties of Sb3+ ion-doped lead-free halide perovskites while examining potential energy transfer pathways across various doping systems. It reviews the recent research progress of Sb3+ ion-doped lead-free perovskites within different frameworks, addressing influencing factors, strategies for enhancing PL intensity, and prospective applications. Ultimately, it outlines the challenges that lie ahead and proposes viable solutions for further exploration of Sb-doped lead-free perovskites.

Eu3+-doped ZnO quantum dots: structure, vibration characteristics, optical properties, and energy transfer process.

This article studies the synthesis, as well as the structural, vibrational, and optical properties of Eu3+-doped ZnO quantum dots (QDs) and investigates the energy transfer mechanism from the ZnO host to Eu3+ ions using Reisfeld's approximation. Eu3+-doped ZnO QDs at varying concentrations (0-7%) were successfully prepared using a wet chemical method. The successful doping of Eu3+ ions into the ZnO host lattice, as well as the composition and valence states of the elements present in the sample, were confirmed through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. XRD results demonstrated the crystalline nature of the ZnO QDs, revealing their wurtzite (WZ) structure with no secondary phases. XPS analysis provided further confirmation of the presence of Eu3+ ions within the ZnO host, with clear signals corresponding to the Zn, O, and Eu elements. The valence states of Eu were verified as trivalent (Eu3+), confirming the successful doping of Eu3+ ions, as evidenced by the characteristic Eu 3d peaks in the XPS spectra. Raman spectroscopy (RS) was employed to analyze the vibrational modes, revealing shifts in ZnO lattice vibrations due to Eu3+ incorporation, indicating strong coupling between Eu3+ ions and the ZnO host. Optical properties were studied using UV-Vis absorption, photoluminescence (PL) spectroscopy, and PL decay spectroscopy, showing a significant enhancement of red emission, attributed to the 5D0 → 7F2 transition of Eu3+ ions under UV excitation. Using Judd-Ofelt (JO) analysis, the intensity parameters (Ω 2, Ω 4, Ω 6) were derived, providing insights into the asymmetry of the Eu3+ ion's local environment and the radiative transition probabilities. Energy transfer processes between the ZnO host and Eu3+ dopants were examined, showing efficient sensitization of Eu3+ through excitation of the ZnO host, with an optimal Eu3+ doping level maximizing luminescence. Eu3+-doped ZnO QDs, which emit in the visible light region and are non-toxic, have great potential for applications in photonic devices, light-emitting diodes, and bioimaging.

Pressure-Induced Emission Enhancement of Multi-Resonance o-Carborane Derivatives via Exciton‒Vibration Coupling Suppression.

Polycyclic multiple resonance (MR) molecules reveal narrowband emission, making them very promising emitters for high color purity display. Nevertheless, they still have challenges such as aggregation-induced emission quenching and spectral broadening. Overcoming these obstacles requires an in-depth understanding of the correlations among the alterations in their geometries, packing structures, and molecular vibrations and their corresponding changes in their photoluminescence (PL) properties. Herein, it is demonstrated that high-pressure infrared, UV-visible absorption, and fluorescence spectroscopies can be combined with computational results to elucidate the influence of the subtle structural variations on the exciton‒vibration couplings and their PL properties. An ortho-carborane-decorated MR emitter (BNC) is a piezochromic molecule and exhibits emission enhancement under high pressure. A thorough analysis of the in situ experimental measurements and calculated results reveals that the pressure-induced changes in the exciton binding energy and exciton‒vibration couplings are responsible for the unusual piezochromism. This research provides insights into the structure‒fluorescence relationship and potential for high-pressure techniques to optimize MR materials for advanced organic light-emitting diodes (OLEDs) applications.

Synthesis and crystallographic characterization of Cu[SeCN

Abstract Copper(I)seleonocyante, Cu[SeCN], is known as a hole-transport layer (THL) material and finds application in transistors and organic light-emitting diodes. Previous works also include a prediction of the crystal structure of Cu[SeCN] by density functional theory analysis. Presumably, as-synthesized Cu[SeCN] forms its α-modification and, if deposited as a layer, it forms its β-modification. However, these statements are based only on the qualitative comparison of the collected and predicted diffraction patterns. Here, we present the complete structural refinement of the crystal structure of α-Cu[SeCN] from powder X-ray diffraction data. α-Cu[SeCN] crystallizes in the α-Cu[SCN] type in the orthorhombic space group Pbca (№ 61) with lattice parameters a = 7.6625(1), b = 6.9628(1), c = 11.2821(2) Å, V = 601.93(1) Å3, and 8 formula units in the unit cell. Moreover, we report on the vibrational (IR/Raman) spectroscopy corroborated by structure optimization and simulation of the spectra by DFT methods, as well as thermal analysis on the basis of differential scanning calorimetry and variable-temperature powder X-ray diffraction.

Blue Electroluminescent Carbon Dots Derived from Victorian Lignite.

Carbon dots (CDs) derived from natural products have attracted considerable interest as eco-friendly materials with a wide range of applications, such as bioimaging, sensors, catalysis, and solar energy harvesting. Among these applications, electroluminescence (EL) is particularly desirable for light-emitting devices in display and lighting technologies. Typically, EL devices incorporating CDs feature a layered structure, where CDs function as the central emissive layer, flanked by charge transport layers and electrodes. Under an applied external bias, electrons and holes are introduced into the active CD layer, resulting in EL through radiative recombination. However, achieving EL with natural product-derived CDs has remained elusive due to challenges such as production difficulties and quenching in the solid state. In this study, we present, for the first time, the successful realization of EL from natural product-derived CDs, synthesized using Victorian lignite through a straightforward single-step pyrolysis method. The CDs demonstrated excellent dispersibility in solvents, allowing them to serve as an emissive layer in light-emitting diodes (LEDs). This was achieved by spin-coating a concentrated CD solution between the organic hole and electron transport layers on a glass substrate coated with indium tin oxide. Remarkably, the CDs retained their dispersibility and emissive efficiency both in solution (toluene) and after film formation. Moreover, the resulting LED demonstrated blue EL, characterized by a peak emission at 460 nm and a maximum luminance of 100.4 cd/m2. This luminance is comparable to that achieved with CDs synthesized from conventional chemical carbon sources. These results highlight the promise of natural product-derived CDs as sustainable and eco-friendly materials for use in LED applications.

Tunable luminescence in Eu3+/Sm3+ doped Na2YMg2V3O12 for WLEDs and optical thermometry.

In recent years, it has become a development trend to design multi-application luminescent materials with rare earth ion doping. In this work, a series of Eu3+/Sm3+ doped self-activated Na2YMg2V3O12 (NYMVO) phosphors were synthesized through a simple high-temperature solid-state reaction method. Interestingly, due to the energy transfer (ET) from the matrix to the activators, the luminescence color of the phosphors changed from turquoise to orange-red and yellow-green under near-ultraviolet (n-UV) 365nm excitation. Based on the fluorescence intensity ratio of the matrix to Eu3+/Sm3+, the optical thermometry performances of the NYMVO:0.20Eu3+ and NYMVO:0.06Sm3+ phosphors were described. Notably, the maximum absolute sensitivity (Sa) values for NYMVO:0.20Eu3+ and NYMVO:0.06Sm3+ phosphors were 0.30K-1 and 0.032K-1, respectively. Correspondingly, the maximum relative sensitivity (Sr) values were 2.17%K-1 and 1.22%K-1, respectively. Moreover, the light-emitting devices based on NYMVO:0.20Eu3+ and NYMVO:0.06Sm3+ phosphors had excellent optical properties, with correlated color temperature (CCT) of 4552 K and 4470 K, and color-rendering index (CRI) of 84.6 and 88.5. These results suggested that the two vanadate phosphors prepared had potential applications in both warm white light-emitting diodes (WLEDs) and optical thermometry.

Strong Enhancement of Light Emission in Core-Shell InGaN/GaN Multi-Quantum-Well Nanowire Light-Emitting Diodes by Incorporating Graphene Quantum Dots.

One-dimensional (1D) vertical nitrides are highly attractive for light-emitting diode (LED) applications because they are useful for overcoming the drawbacks of conventional GaN planar structures. However, the internal quantum efficiency (IQE) of GaN multi-quantum-well (MQW) nanowire (NW) LEDs, typical 1D GaN structures, is still too low to replace standard planar LEDs. Here, we report a phenomenon of light amplification from core-shell InGaN/GaN NW LEDs by incorporating graphene quantum dots (GQDs). The photoluminescence (PL) and electroluminescence (EL) intensities are greatly enhanced when GQDs of 5, 10, and 20 nm size are located solely in the MQWs or both in the MQWs and on the p-GaN surface, but much fewer PL and EL increases are observed for 30 and 40 nm GQDs, consistent with the size-dependent optical output power (OOP) and light-extraction efficiency (LEE). The carrier transfer between GQDs and MQWs is strongly affected by the size-dependent band-gap variation and the band profile depending on whether the forward bias is applied on the LED or not. This explains why the PL and EL spectra show different size dependences of the GQDs. The variation of the OOP by the inclusion of GQDs in the LED turns out to be governed by the IQE rather than by the LEE. Our findings highlight remarkable enhancement of light emission from GaN MQW NW LEDs by a simple approach of incorporating GQDs in the MQWs and on the p-GaN surface, also very promising for applications in a wide range of optoelectronic devices.

Theoretical investigation of the electro-optical properties of new II-conjugated molecules based on phenyl and pyrrole for organic light-emitting diodes (OLED) applications: a DFT approach

Theoretical investigation of the electro-optical properties of new II-conjugated molecules based on phenyl and pyrrole for organic light-emitting diodes (OLED) applications: a DFT approach

Mechanochemical Synthesis of Phase-Pure CsCu2I3 and Cs3Cu2I5 Phosphors Regulated by Polar Solvents and Their Application in Tunable Chromaticity LEDs.

Lead halide perovskites have garnered interest in light-emitting diode (LED) applications due to their strong emission and tunable properties. However, conventional synthesis methods involve energy-intensive thermal processes and hazardous organic solvents, raising environmental concerns. In this study, we report a simple and eco-friendly mechanochemical approach that produces phase-pure blue-emitting Cs3Cu2I5 (emission at 440 nm) and yellow-emitting CsCu2I3 (emission at 570 nm) phosphors through polarity modulation and control of grinding duration. Our comprehensive analysis of the phase transitions during mechanochemical synthesis reveals that pure Cs3Cu2I5 was synthesized from a 3:2 precursor molar ratio in ethanol for 30 min, while pure CsCu2I3 was obtained from a 1:2 precursor molar ratio in an aqueous solution for 7.5 min. Moreover, Raman spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy analyses confirmed that phase-pure phosphors were achieved through these methods. Finally, we fabricated a series of color-adjustable LEDs by mixing Cs3Cu2I5 and CsCu2I3 phosphors in different proportions. This demonstrates the potential of our mechanochemical synthesis for the efficient, large-scale production of next-generation lighting materials with tunable emission.

A Multiresonant Thermally Activated Delayed Fluorescent Dendrimer with Intramolecular Energy Transfer: Application for Efficient Host-Free Green Solution-Processed Organic Light-emitting Diodes.

The development of narrowband emissive, bright, and stable solution-processed organic light-emitting diodes (SP-OLEDs) remains a challenge. Here, a strategy is presented that merges within a single emitter a TADF sensitizer responsible for exciton harvesting and an MR-TADF motif that provides bright and narrowband emission. This emitter design also shows strong resistance to aggregate formation and aggregation-cause quenching. It is based on a known MR-TADF emitter DtBuCzB with a donor-acceptor TADF moiety consisting of either tert-butylcarbazole donors (tBuCzCO2HDCzB) or second-generation carbazole-based donor dendrons (2GtBuCzCO2HDCzB) and a benzoate acceptor. The TADF moiety acts as an exciton harvesting antenna and transfers these excitons via Förster resonance energy transfer to the MR-TADF emissive core. The SP-OLEDs with 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB thus show very high maximum external quantum efficiencies (EQEmax of 27.9 and 22.0%) and minimal efficiency roll-off out to 5000cd m-2.

Uncovering the Performance Enhancing Mechanism of Methanesulfonate Ligands in Perovskite Quantum Dots for Light-Emitting Devices.

Perovskite quantum dots (PQDs) have attracted more and more attention in light-emitting diode (LED) devices due to their outstanding photoelectric properties. Surface ligands not only enable size control of quantum dots but also enhance their optoelectronic performance. However, the efficiency of exciton recombination in PQDs is often hindered by the desorption dynamics of surface ligands, leading to suboptimal electrical performance. In this study, sodium methanesulfonate (NaMeS) was successfully introduced during PQD synthesis and ligand exchange, where the S═O groups effectively interacted with the perovskite components. The NaMeS-modified PQD films exhibited significantly improved surface morphology, radiative recombination efficiency, and carrier mobility. Consequently, Pe-LEDs derived from NaMeS-capped PQDs achieved a remarkable enhancement in performance with a maximum external quantum efficiency of 9.41%. This work thus provides a novel and effective strategy for the development of high-performance PQDs and their applications in LEDs.

How Structure and Hydrostatic Pressure Impact Excited-State Properties of Organic Room-Temperature Phosphorescence Molecules: A Theoretical Perspective.

Organic room-temperature phosphorescence (RTP) emitters with long lifetimes, high exciton utilizations, and tunable emission properties show promising applications in organic light-emitting diodes (OLEDs) and biomedical fields. Their excited-state properties are highly related to single molecular structure, aggregation morphology, and external stimulus (such as hydrostatic pressure effect). To gain a deeper understanding and effectively regulate the key factors of luminescent efficiency and lifetime for RTP emitters, we employ the thermal vibration correlation function (TVCF) theory coupled with quantum mechanics/molecular mechanics (QM/MM) calculations to investigate the photophysical properties of three reported RTP crystals (Bp-OEt, Xan-OEt, and Xan-OMe) with elastic/plastic deformation. By analyzing the geometric structures and stacking modes of these crystals, we observe that the geometric structure variations influence the electronic structures, subsequently modifying the transition properties and the energy consumption processes. Specifically, the presence of strong π-π interactions and hydrogen bonds in the Xan-OEt crystal inhibits a nonradiative decay process, thereby realizing long-lived emission. Additionally, the hybridized local and charge-transfer (HLCT) excited-state feature with the largest charge transfer excitation contributions (57.74%) for Xan-OEt stabilizes the triplet excitons and facilitates the radiative decay process, ultimately achieving high efficiency and long lifetime emissions. Furthermore, by applying high hydrostatic pressure for the Bp-OEt crystal, the RTP emission efficiencies and lifetimes are enhanced and blue-shifted. All of these results demonstrate the crucial role of molecular structure and stacking modes as well as the hydrostatic pressure effect in regulating RTP properties. Thus, our findings reveal the structure-packing-property relationship and highlight the control of molecular packing and the related tunable approaches, which could provide prospective strategies for constructing stimuli-responsive RTP emitters in practical applications.

Opportunities and challenges of lead-free metal halide perovskites for luminescence.

Metal halide perovskites (MHPs) have been developed rapidly for application in light-emitting diodes (LEDs), lasers, solar cells, photodetectors and other fields in recent years due to their excellent photoelectronic properties, and they have attracted the attention of many researchers. Perovskite LEDs (PeLEDs) show great promise for next-generation lighting and display technologies, and the external quantum efficiency (EQE) values of polycrystalline thin-film PeLEDs exceed 20%, which is undoubtedly a big breakthrough in lighting and display fields. However, the toxicity and instabilities of lead-based MHPs remain major obstacles limiting their further commercial applications. The exploration and development of lead-free MHPs (LFMHPs) are regarded as the most facile strategies to solve these problems. Compared with lead-based perovskites, LFMHPs exhibit better stabilities and broadband emission. With continuous development of LFMHPs, their photoluminescence quantum yields (PLQYs) have reached 99%, facilitating their use as ideal emitters. In this review, the structures and features of LFMHPs are analyzed, and the preparation methods of LFMHPs with various structures and configurations are discussed. Then, the mechanisms and strategies for improving the emission performance of white LEDs based on LFMHPs are demonstrated. Finally, their challenges in commercial production and perspectives are prospected.

Phosphor-converted light-emitting diodes in the marine environment: current status and future trends.

The exploitation and utilization of resources in marine environments have ignited a demand for advanced illumination and optical communication technologies. Light-emitting diodes (LEDs), heralded as "green lighting sources", offer a compelling solution to the technical challenges of marine exploration due to their inherent advantages. Among the myriad of LED technologies, phosphor-converted light-emitting diodes (pc-LEDs) have emerged as frontrunners in marine applications. At the heart of pc-LEDs lie phosphor materials, colour-converters that orchestrate the emission of light. In the marine environment, blue-green light with a wavelength of 440-570 nm exhibits the deepest penetration depth, while other wavelengths are rapidly attenuated in the shallow layer. Additionally, specific wavelengths of light are crucial for particular applications. However, the moist marine environment as well as the demand for continuous and stable lighting pose a formidable challenge to the environmental stability of the phosphors. Therefore, developing blue-green phosphors with exceptional colour purity and high thermal and moisture stability is paramount for marine applications. Herein, this review delves into the application of LED and pc-LED technology in underwater optical communication and marine fishery, exploring the development strategies of phosphors tailored for the marine environment. The insights presented serve as a valuable reference for further research on phosphors and pc-LED devices.

Novel Photodynamic Inactivation Strategy for Salmonella Enteritidis PT4 on Eggshells: Exploiting the Antimicrobial Potential of Curcumin and Carvacrol.

Photodynamic inactivation (PDI) is a new and promising strategy for eliminating foodborne pathogenic bacteria in food preservation, reducing associated health risks for consumers. This study aimed to develop an innovative PDI-based system to inactivate Salmonella Enteritidis PT4 on eggshells. The system includes 405nm light-emitting diodes (LEDs) and the application of curcumin or carvacrol as photosensitizers. The antibacterial activity of the system was investigated in eggshells inoculated with S. Enteritidis PT4 at different temperatures (4, 25, and 37°C) and exposure times (15, 30, and 45min). Carvacrol + LEDs application was completely inhibited S. Enteritdis PT4 at 4 (after 30 min), 25, and 37°C at the 45th min. Curcumin + LED completely inhibited bacterial growth after 45min at 4 and 25°C. The results showed that simultaneous use of carvacrol or curcumin with LEDs at various temperatures exhibited significant antibacterial activity against the bacteria depending on the exposure time. The application of curcumin or carvacrol sourced via PDI in the originally developed system resulted in any significant changes in egg quality parameters and sensory properties. This study demonstrated that PDI-based system using curcumin or carvacrol as photosensitizers could be a potential tool for decontamination of eggs contaminated with S. Enteritidis PT4.

Crystal Structure and Photoluminescence Properties of Ca3(PO4)2:Eu3+ Phosphors With High Emission Efficiency.

The influence of Eu3+ concentration on the crystal structure and photoluminescence (PL) properties of Ca3-x(PO4)2:xEu3+ (0.06 ≤ x ≤ 0.10) phosphors is systematically investigated using X-ray diffraction (XRD) Rietveld refinement, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, UV-visible spectroscopy, and PL spectroscopy. The prepared phosphors exhibit a single rhombohedral phase with the space group R3c. The constituent ions occupy various crystallographic sites, including Ca(1-5), Eu(1-3), P(1-3), and O(1-10) sites. Under 397-nm excitation, the emission spectra show distinct emission peaks between 525 and 725 nm, corresponding to the 5D1 → 7Fj (j = 1 and 2) and 5D0 → 7Fj (j = 1, 2, 3, and 4) transitions of Eu3+ ions. The concentration quenching observed in the phosphors is attributed to electric multipolar interactions. Among the prepared phosphors, Ca2.92(PO4)2:0.08Eu3+ phosphor shows the highest emission efficiency and excellent color performance. These results demonstrate that Ca3-x(PO4)2:xEu3+ phosphors have significant potential as red-emitting materials for white light-emitting diode (WLED) applications.

Strain-engineered bright excitons and a nearly flat band in monolayer SnNBr for high-speed LED applications.

With the ever-increasing volume of data, the need for systems that can handle massive datasets is becoming gradually critical. High performance visible light communication (VLC) systems offer an expedient solution, yet its widespread adoption is hindered by the limited modulation bandwidth of light emitting diodes (LEDs). Through ab initio many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation (BSE) approach, this work introduces a novel approach to achieving exceptionally high modulation bandwidth by utilizing the nearly flat bands in two-dimensional semiconductors, using SnNBr monolayer as a prototype material for overcoming this bottleneck. Utilizing its unique properties of a direct bandgap and a nearly flat highest valence band, we demonstrate the achievement of exceptionally high modulation bandwidths on the order of terahertz, surpassing the capabilities of established materials such as InGaN and GaN. Interestingly, the excellent absorption and recombination features of the SnNBr monolayer can be modulated further by the application of in-plane tensile strain. The strain-induced proliferation of bright excitons in the visible region, coupled with enhanced absorption and accelerated recombination rates, provides a deeper understanding of the fundamental mechanisms at play in two-dimensional materials, laying the groundwork for future explorations in light-matter interactions at terahertz frequencies.

Highly Humidity-Resistant Oxynitride Phosphor BaSi6N8O:Ce3+ for pc-LEDs.

Many phosphor hosts, for example, nitrides and sulfides, often face challenges such as hydrolysis and oxidation, limiting their application in phosphor-converted white light-emitting diodes (pc-LEDs). In this study, we developed a highly humidity-resistant yellow-green-emitting phosphor BaSi6N8O:Ce3+ (BSNO:Ce3+). The DFT calculations revealed a high Debye temperature (ΘD = 1159 K), indicating a rigid crystal structure that contributes to the photoluminescence thermal quenching resistance of BSNO. Furthermore, we observed a notable positional shift of Ce3+ in the BSNO lattice, contributing to an unusual photoluminescence (PL) red shift compared to BSNO:Eu2+. Importantly, BSNO:Ce3+ exhibited remarkable PL stability under harsh conditions, showing no degradation in water for 10 days and less than 10% intensity loss at elevated temperatures up to 773 K. We constructed a prototype white LED with a high color rendering index (Ra = 92) by combining a 365 nm chip with BSNO:0.03Ce3+ and commercial phosphors, demonstrating its potential for advanced pc-LED applications.

Synthesis and Characterization of Functionalized Poly(9-vinylcarbazole) for light-emitting diode applications

Organic light-emitting diode (OLED) has been successfully applied to replace conventional lighting systems due to its ability to adjust color emission, low energy consumption, and high contrast ratio. One of the polymers of interest in this area is polyvinyl carbazole, PVK, given its characteristics, such as forming stable radicals, high thermal and photochemical stability, and high charge carrier mobility. The modification of PVK has contributed positively to its performance as an electroluminescent layer in the constitution of OLED devices, as seen in works carried out by Mota & Marques (2019); Brito & Marques (2020); Correia & Marques (2022); Geffroy & Grana (2019); Pachariyangkun & Suda (2020). The present study aimed to synthesize and functionalize poly(9-vinylcarbazole) as well as its characterization by thermoanalytical (TG, DTA and DSC) and spectroscopic (FTIR) techniques in order to verify the efficiency of the proposed synthesis. To date, no studies have been found in the literature using the compound 3-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-dibenzofuran in PVK for application in the emitting layer of optoelectronic devices.