Strong Light Emission Research Articles

Fabrication of Eu2O3 doped in high density and transparent silicoborate scintillating glass for synchrotron X-ray radiographic imaging application

In this work, the glass system, xEu2O3 - 10SrO - 20La2O3 - 10Ta2O5 - 10SiO2 - (50-x)B2O3, where x = 0, 1, 3, 5, 7, 9, 11 mol%, was fabricated using the high-temperature melt quenching method. The physical, optical, and luminescence properties of the glass were investigated to determine its suitability as a scintillation material. The transparent glass sample showed a high density and molar volume up to 4.72 g/cm3 and 40.57 cm3/mol, respectively, reflecting that higher NBOs in glass matrix. This result is also supported by X-rays photoelectron spectroscopy (XPS) spectra. Absorption spectra represented peaks in the ultraviolet to near infrared regions, which can be confirmed the presenting of Eu3+ ion in glass matrix. Under UV excitation, the glass doped with 3 mol% of Eu2O3 shows highest intensity while scintillation light (X-rays induced luminescence) was highest performed at 7 mol%. The integral intensity of radioluminescence of glass is 26 % that of commercial BGO scintillator. The photoluminescence quantum yield (PLQY) was measured and the highest PLQY was correspond with emission intensity. The glass scintillator was used for X-ray imaging at beamline 1.2, Synchrotron Light Research Institute (SLRI), Thailand and the spatial resolution was evaluated. Due to the strong light emission at 615 nm from 5D0 → 7F2 transition of Eu3+, this developed scintillating glass has a potential for X-ray imaging material in radiographic application.

Development of highly thermal-stable blue emitting Y4Al2O9:Bi3+ phosphors for w-LEDs, fingerprint and data security applications

A new blue-emitting Y4Al2O9:Bi3+ (YAO:Bi3+) phosphor is synthesized using the solution combustion method with mushroom extract as a binder. Its structural properties, concentration effects, temperature-dependent luminescence, and performance in LED devices are thoroughly investigated. Upon excitation at 367 nm, a strong blue light emission at 423 nm is observed, attributed to the 3P1→1S0 transition of Bi3+. The quantum efficiency reached approximately 63.5 %. The CIE diagram shows that the emission colour falls within the intense blue region, achieving a colour purity (CP) of 94 %. YAO:Bi3+ exhibits strong absorption in the near-ultraviolet range (330–400 nm), making it suitable for LEDs powered by near-ultraviolet chips. A thermal quenching experiment revealed an activation energy (Ea) of 0.323 eV, indicating that this YAO:Bi3+ phosphor possesses good thermal stability. This study showcases the use of YAO:Bi3+ phosphor in encapsulated LED devices. The device’s Commission Internationale de l’Éclairage (CIE) coordinates are (0.325, 0.310), with a high colour rendering index (CRI) of 94.70 and a low correlated colour temperature (CCT) of 5915 K at a current of 120 mA. These properties indicate that this phosphor is suitable for developing white LED devices powered by near-ultraviolet chips. The optimized YAO:Bi3+ phosphor is employed to enhance the detection of Level I-III fingerprint (FP) details with high resolution and contrast, showing effective visualization of latent fingerprints (LFPs) on various substrates. Furthermore, it is used as a model for developing fluorescent ink, which is applied to different media. The results suggest that YAO:Bi3+ phosphor has significant potential for applications in w-LEDs, advanced forensics, and anti-counterfeiting ink technologies.

Preparation and scintillation properties of Eu3+-doped high crystallinity tellurite glass ceramics

In this study, a high-crystallinity glass-ceramic scintillator doped with Eu³⁺ containing Bi₂Te₄O₁₁ nanocrystals was prepared using a traditional melt crystallization method. The optimal heat treatment conditions, phase structure, and luminescent properties of the glass-ceramics were systematically investigated using various characterization techniques, including DSC, XRD, SEM, and spectrophotometry. To achieve glass-ceramic samples with high transmittance and excellent luminescent performance, the optimal heat treatment process was determined to be 500 °C for 10 min. The final sample was found to have a density of 5.9 g/cm³ and a crystallinity of 70 %. Strong orange-red light emission was exhibited by the glass-ceramic under both 465 nm light and X-ray excitation. The maximum integral X-ray excited luminescence (XEL) intensity was found to reach 20.2 % of that of the commercial Bi4Ge3O12 (BGO) scintillation crystal. It is indicated by the research that Eu³⁺-doped high-crystallinity tellurate glass-ceramics are promising candidate materials for scintillators in the field of X-ray detection.

Biological Cavity Quantum Electrodynamics via Self-Aligned Nanoring Doublets: QED-SANDs.

Quantum mechanics is applied to create numerous electronic devices, including lasers, electron microscopes, magnetic resonance imaging, and quantum information technology. However, the practical realization of cavity quantum electrodynamics (QED) in various applications is limited due to the demanding conditions required for achieving strong coupling between an optical cavity and excitonic matter. Here, we present biological cavity QED with self-aligned nanoring doublets: QED-SANDs, which exhibit robust room-temperature strong coupling with a biomolecular emitter, chlorophyll-a. We observe the emergence of plasmon-exciton polaritons, which manifest as a bifurcation of the plasmonic scattering peak of biological QED-SANDs into two distinct polariton states with Rabi splitting up to ∼200 meV. We elucidate the mechanistic origin of strong coupling using finite-element modeling and quantify the coupling strength by employing temporal coupled-mode theory to obtain the coupling strength up to approximately 3.6 times the magnitude of the intrinsic decay rate of QED-SANDs. Furthermore, the robust presence of the polaritons is verified through photoluminescence measurements at room temperature, from which strong light emission from the lower polariton state is observed, while emission from the upper polariton state is quenched. QED-SANDs present significant potential for groundbreaking insights into biomolecular behavior in nanocavities, especially in the context of quantum biology.

Optical Applications of CuInSe2 Colloidal Quantum Dots.

The distinctive chemical, physical, electrical, and optical properties of semiconductor quantum dots (QDs) make them a highly fascinating nanomaterial that has been extensively studied. The CuInSe2 (CIS) QDs demonstrates great potential as a nontoxic alternative to CdSe and PbSe QDs for realizing high-performance solution-processed semiconductor devices. The CIS QDs show strong light absorption and bright emission across the visible and infrared spectrum and have been designed to exhibit optical gain. The special characteristics of these properties are of great significance in the fields of solar energy conversion, display, and electronic devices. Here, we present a comprehensive overview of the potential applications of colloidal CIS QDs in various fields, with a particular focus on solar energy conversion (such as QD solar cells, QD-sensitized solar cells, and QD luminescence solar concentrators), solar-to-hydrogen production (such as photocatalytic and photoelectrochemical H2 production), and QD electronics (such as QD transistors, QD light-emitting diodes, and QD photodetectors). Furthermore, we offer our insights into the current challenges and future opportunities associated with CIS QDs for further research.

Synthesis, enantiomeric separation and (chir)optical properties of [7]helicene derivatives for OLED applications. A comprehensive experimental and computational investigation

A two–step photochemical process was employed to synthesize new racemic [7]helicenes with appropriate functional groups, resulting in an overall yield of 61 % to 74 %. These helical species showed good solubility in common solvents and confirmed structurally through various spectroscopic methods. In solution, they exhibited strong absorption (λabs = 250–500 nm) and blue light emission with a fluorescence quantum yield (Φ) ranging from 7 % to 26 %. Experimental analysis of their HOMO and LUMO energy levels highlighted an irreversible electrochemical behavior and a band gap (Eg–el) of 2.60 eV to 2.64 eV. The helicenes were successfully separated by chiral HPLC, yielding P and M–enantiomers in high optical purity (>98.5 % up to >99.5 % ee) that demonstrated substantial optical rotations (e.g., +3700–5000 for the P–enantiomer at λ = 589 nm) and notable electronic circular dichroism (ECD) signals. Density functional theory (DFT) was undertaken to establish connections between diverse structure-properties relationships and precisely replicate the experimental findings. Ultimately, these helical species, with notable performance in emission, electrochemical behavior, and thermal stability, can effectively serve as blue-emitting chiral dopants in OLED devices and as hole-transport units.

Enhancing photoluminescence of WSe2 in vapor grown WSe2/VOCl bilayer heterojunctions via surface passivation.

Monolayer tungsten selenide (WSe2) has attracted attention due to its direct bandgap-generated strong light emission and light-matter interaction. Herein, vertical WSe2/VOCl bilayer heterojunctions with enhanced PL of WSe2 were synthesized by the vapor growth method. The morphology, crystal structure, and chemical composition of the WSe2/VOCl heterojunctions were systematically investigated, which confirmed the successful formation of the heterojunctions. The PL emission intensity of WSe2 obtained from the WSe2/VOCl heterojunction was about 2.4 times higher than that of the WSe2 monolayer, demonstrating the high optical quality of the WSe2/VOCl heterojunction, which was further confirmed by time-resolved PL measurements. The insulator top VOCl, which was deposited on the surface of the semiconductor bottom WSe2 as a surface passivation material, reducing the impurities and resulting in an atomically clean surface, successfully enhanced the PL emission of the bottom WSe2. This vertical WSe2/VOCl bilayer heterojunction with PL enhancement could provide a promising platform for optical devices.

Ultrafast Visual Detection of a Trace Amount of Water by Highly Efficient Hybrid Manganese Halides.

A quantitative water detection method is urgently needed in storage facilities, space exploration, and the chemical industry. Although numerous physical techniques have been widely utilized to determine the water content, they still suffer from many disadvantages such as highly expensive special instruments, complicated analysis processes, etc. Hence, a convenient, rapid, and sensitive water analysis method is highly desirable. Herein, we developed a visual fluorescence sensing technology for water detection based on reversible PL off-on switching of organic-inorganic hybrid zero-dimensional (0D) manganese halides. In this work, a family of hybrid manganese halides were synthesized through a facile solution method, namely, [NH4(18-Crown-6)]2MnBr4, [Ca(18-Crown-6)·3H2O](18-Crown-6)MnBr4, [NH4(dibenzo-18-Crown-6)]2MnBr4, and [Ca(dibenzo-18-Crown-6)·2H2O]MnBr4. Excited by UV light, these highly crystalline manganese halides exhibit strong green light emissions from the d-d electron transition of Mn2+ with near-unity photoluminescence quantum yield and submillisecond lifetime. Benefiting from the dynamic and weak ionic bonding interactions, these 0D manganese halides display reversible water-response on/off luminescence switching but fail in any other aprotic solvents. Therefore, these 0D hybrid manganese halides can be explored as ultrafast visual fluorescence probes to detect the trace amount of water in organic solvents with multiple superiorities of rapid response time (< 2 s), ultralow detection limit (9.71 ppm), excellent repeatability, etc. The reversible water-response luminescent on/off switching also provides a binary optical gate with advanced applications in anticounterfeiting and information security, etc.

Rare-Earth-Metal-Free Solid-State Fluorescent Carbonized-Polymer Microspheres for Unclonable Anti-Counterfeit Whispering-Gallery Emissions from Red to Near-Infrared Wavelengths.

Colloidal carbon dots (CDs) have garnered much attention as metal-free photoluminescent nanomaterials, yet creation of solid-state fluorescent (SSF) materials emitting in the deep red (DR) to near-infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro-resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram-scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross-linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation-induced quenching (AIQ), enabling strong solid-state light emission. Both experimental and theoretical analysis support a role for extended π-conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within these microstructures, which exhibit a progressive red shift in light absorption/emission toward the NIR range. Moreover, the highly spherical shape of CPMs endows them with innate photonic functionalities in combination with their intrinsic CD-based attributes. Harnessing their excitation wavelength-dependent photoluminescent (PL) property, a single CPM exhibits whispering-gallery modes (WGMs) that are emission-tunable from the DR to the NIR. This type of newly developed microresonator can serve as, for example, unclonable anti-counterfeiting labels. This innovative cross-cutting approach, combining photonics and chemistry, offers robust, bottom-up, built-in photonic functionality with diverse NIR applications.

High-efficiency luminescent Eu3+ heavily doped glass prepared from black talc: A promising material for significant applications in W-LED illumination

As a distinguished luminescent matrix, rare earth (RE)-doped glass has garnered considerable attention across lighting, display, laser, and related domains. Nonetheless, the limited luminescent efficiency of such glass imposes constraints on its extensive utilization. In addressing this challenge, we have developed a novel formulation involving heavily Eu3+-doped black talc glass, boasting exceptional optical characteristics. Structural examination has validated the successful synthesis of the parent glass matrix comprising [SiO4] and [AlO4] units. With the escalating of Eu3+ doping concentrations, the glass manifested an upward trend in both density and refractive index. Under the excitation of 393 nm light, the glass exhibited strong red light emission, demonstrating a high internal quantum efficiency (IQE) of up to 84.67 %, surpassing markedly other Eu3+-doped glass variants. Furthermore, even under elevated temperatures reaching 150 °C, the glass retained 86.2 % of its luminescent intensity at room temperature, indicative of superior thermal resilience vis-à-vis alternative glass systems. As a proof-of-concept, we encapsulated a white light-emitting diode (W-LED) assembly employing a 395 nm LED chip, Eu3+-doped glass, BaMgAl10O17:Eu2+ blue phosphor, and Ba2SiO4:Eu2+ green phosphor. The resultant device exhibited favorable chromaticity coordinates (0.3566, 0.3994), boasting a correlated color temperature (CCT) of 4791K and a high color rendering index (CRI) of 91. In summary, this investigation employs black talc ore to synthesize luminescent glass, thereby not only diversifying the application scope of black talc but also augmenting its additional value, while notably enhancing the luminescent efficiency of the glass through heavy Eu3+ doping. Through empirical validation, the significant potential benefits of Eu3+-doped black talc glass in the realm of W-LED lighting were convincingly demonstrated.

Adjusting photoluminescence of high thermostability Dy3+/Eu3+ co-doped borosilicate glass for white LED device

Due to the adoption of fluorescent powder encapsulated by organic resin, commercial light emitting diodes (LEDs) suffer from low thermal stability and poor light quality under high temperature, and luminescent glass is one of the effective ways to solve this problem. A series of borosilicate (B2O3–SiO2–Al2O3–PbO-Dy2O3–Eu2O3, marked as BSAP: DyEu) was prepared by the gas suspension technique. The basic characterization test indicate that the prepared glass has excellent thermal stability and stable structure. The optical properties of the luminescent glass were investigated in detail. By changing the Eu3+ doping amount, the Dy3+/Eu3+ co-doped glass can realize warm white light emission. The temperature-variable fluorescence spectra of BASP: Dy1.25Eu1.0 were analyzed, and the glass can produce strong warm white light emission in a wide temperature range. At 700 K, the luminous intensity of the glass remains above 38.49 % of the room temperature, and the chroma shift ΔC = 8.57 × 10−3. In addition, the w-LED device based on commercial GaN chip and BSAP: DyEu glass realizes warm white light output with excellent correlated color temperature (3063 K) and high color rendering index (90.3). The analysis shows that Dy3+/Eu3+ co-doped borosilicate glass can be used as a candidate material for w-LED applications.

Luminescence of Tm3+, Yb3+ Co-doped CaLaAlO4/LaAlO3 Mixed Phase Phosphor for Solid-state Lighting Application

CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ upconversion phosphors were prepared via the combustion method. The Tm3+ dopant concentration was constant (Tm=0.5mol%), while the concentration of Yb3+ co-dopant was varied (Yb = 1 – 10 mol%). The X-ray diffraction studies indicated a mixture of phases (tetragonal and hexagonal of CaLaAlO4 and LaAlO3 respectively). The optical absorption spectra of the upconversion phosphors have two absorption bands centered at 253 nm, and another band at 440 nm. The band at 253 nm is ascribed to the charge transfer band (CTB) between the ligand (O2-) and Yb3+ ions, while the broad band located at 440 nm was related to defect states in the lattice. The energy bandgap and refractive index of the optimized phosphor were 4.73 eV and 1.76 respectively. The upconversion emission peaks centered at 478 nm (1G4 → 3H6), 654 nm (1G4 → 3F4), and 801 nm (3H4 → 3H6) are associated to the electronic transitions of Tm3+ ions. As the Yb concentration increases, the colour emission is tuned from bluish white to blue light. The CCT and CIE coordinate of (0.2419, 0.2463) showed that the phosphor doped with 10 mol% of Yb3+ produces a bluish-white and its colour purity was 80%. Thus, the strong bluish-white light emission produced by the CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ phosphors could be used for solid-state lighting (SSL) or in multicolour displays.

Effects of Heavy p‐Block Elements on Photophysical Properties of π‐Conjugated Complexes and Organoelement Compounds

π‐Conjugated compounds exhibit remarkable photophysical properties, such as strong light absorption and emission, and are applicable to organic devices, bioimaging, and sensing systems. The introduction of p‐block elements into π‐conjugated systems is presumable as a critical strategy for modulating their properties. Nevertheless, the type of utilized elements has been limited to the second and third‐period ones because it is difficult to construct critical electronic interactions between heavier atoms and carbon‐based π‐conjugated scaffolds. On the other hand, it has been recently suggested that the heavier p‐block elements are able to induce significant changes in the optoelectronic properties of π‐conjugated systems thanks to their large size, high polarizability, and heavy atom effect. Although there are much room to explore effects of heavy‐atom substitution on physical and electronic properties of conjugated systems, various characters have been discovered. Hence, this review mainly focuses on the relationships between the types of p‐block elements and the optical properties of their representative complexes and organoelement compounds, particularly light absorption and emission.

Effect of Tb3+ and Ce3+ Co-doping on the Structure and Photoluminescence Properties of Hexagonal Boron Nitride Phosphors.

In the paper, we have successfully prepared hexagonal boron nitride (h-BN:Tb3+, Ce3+) phosphors with melamine as the nitrogen source. The X-ray powder diffraction patterns confirm that the sample possesses a hexagonal crystal structure within the P m2 space group. It is interesting that the co-doping combination of Tb3+ and Ce3+ can markedly enhance the threshold concentration of doped activators within the limited solid solution of h-BN phosphors. Under 302nm excitation, the h-BN:Ce3+ phosphors exhibit broadband blue light emission at 406nm. In h-BN:Tb3+, Ce3+ phosphors, the co-doping of Ce3+ not only ensures high phase purity but also results in strong green light emission. The energy transfer efficiency from Ce3+ to Tb3+ is about 55%. The fluorescence lifetime increases with the increase of Ce3+ and Tb3+ concentration, and the fluorescence lifetime of h-BN:0.025Tb3+, 0.05Ce3+ phosphor reached 2.087ms. Additionally, the h-BN:0.025Tb3+, 0.05Ce3+ phosphor exhibits excellent thermal performance with an activation energy value of 0.2825eV. Moreover, the photoluminescence quantum yield of the sample exceeds 52%. Therefore, the h-BN:Tb3+, Ce3+ samples can be used as green phosphors for solid state lighting and fluorescent labeling.

Enhancing the Water‐Stability of 1D Hybrid Manganese Halides by a Cationic Engineering Strategy

AbstractAlthough the luminescent performance of organic–inorganic metal halides (OIMHs) have obtained significant advances, achieving intrinsic water‐stable OIMHs remain a substantial challenge due to the fragile ionic nature of hybrid the halide structure. To overcome these challenges, a structural design strategy is proposed that involves the use of highly hydrophobic cations as a protective layer to improve the water stability of OIMH. Herein, an aprotic trimethylsulfoxonium [TMSO]+ is selected as a hydrophobic cation and successfully assemble two new manganese based OIMHs of (TMSO)MnCl3 and (TMSO)MnBr3 through facile solid and liquid phase reaction methods. Remarkably, these halides exhibit strong red light emissions with high quantum yields recorded at 86.1% and 53.4%, respectively, originating from the octahedral [MnX6]4− based one‐dimensional (1D) [MnX3]− chain. Most significantly, these halides present extraordinary structural and luminescent stabilities toward continuous corrosion by humid air, water, and acid‐aqueous solution for more than one month, suggesting promising application prospects in extreme chemical environments. In‐depth Hirshfeld surface calculations demonstrate that the ultrahigh water‐stability benefits from the abundant hydrogen bonds and strong electrostatic interactions between [TMSO]+ and [MnX3]− ions, which provides an underlying insight into the stability mechanism. This water‐stability enhancement strategy represents a breakthrough structural engineering to rationally design more water‐stable OIMH.

Energy balance and global characteristics of metal dust flames

Recently demonstrated high values of radiative loss during metal combustion require a new approach to describing dust flames. In particular, given strong light emission, the adiabatic flame temperature (AFT) concept is not applicable due to high radiative losses. Accordingly, global flame characteristics such as an expansion factor become unrelated to the AFT. That expansion factor can be directly inferred from the flame geometry, and therefore, its analysis offers a simple path to justify the need for a detailed energy balance in metal dust combustion. The analysis can also provide insight into peculiarities of the temperature distribution within the flame. In the current paper, previously published data on flow velocities in a metal dust flame are used for the expansion factor analysis. A relatively low value of the obtained expansion factor is reconciled with the advanced comprehension of metal particle combustion.

Cd-MOF and Its Ln3+-Post Modification Products: Regulation of Luminescence Properties and Improved Detection of Uric Acid, Quinine, and Quinidine.

One 3D Cd-MOF, namely, {[(HDMA)2][Cd3(L)2]·5H2O·2DMF}n (LCU-124, LCU indicates Liaocheng University), was synthesized from an ether-containing ligand 1,3-bis(3,5-dicarboxylphenoxy)benzene (H4L). Its Ln3+-postmodified samples, Eu3+@LCU-124 and Tb3+@LCU-124, were obtained through cation exchange of dimethylamine cation (HDMA) with Eu3+ and Tb3+. The successful entry of rare earth into LCU-124 by cation exchange modification was verified by IR, XRD, XPS, EDS mapping, and luminescence spectra. The proportion of Eu3+/Tb3+ was adjusted during the modification process, leading to fluorescent materials with different emissions. Luminescence measurements indicated that these complexes exhibited interesting multiresponsive sensing activities toward biomarkers urine acid (UA), quinine (QN), and quinidine (QND). First, LCU-124 has a pronounced quenching effect toward UA with the detection limit of 31.01 μM. After modification, the visualization of the detection was improved significantly and the detection limit of Eu3+@LCU-124 was reduced to 0.868 μM. Second, when QN and QND were present in the suspensions of Eu3+@LCU-124 and Tb3+@LCU-124, strong blue light emission peaks occurred, while the characteristic emission of Eu3+/Tb3+ decreased, forming ratiometric fluorescent sensors with the detection limit in the range of 0.199-9.49 μM. The fluorescent probes have high selectivity, excellent sensitivity recycling, and fast response time (less than 1 min). Besides, a simple logic gate circuit and a range of luminescent mixed matrix membranes were designed to provide simple and fast detection of above biomarkers. Our work indicated that modification of Eu3+/Tb3+ could improve the detection ability significantly.

Red light intensity modulation, temperature sensing and bioimaging of NaLuF4:Er3+/Tm3+/Yb3+ microcrystals under 1532 nm laser excitation

This paper reports on microcrystals with deep tissue penetration depth, strong red light emission, and thermometric function. The red light emission of NaLuF4:20 % Er3+/1 % Tm3+/10 % Yb3+ microcrystals is exceptionally strong, thanks to the introduction of Tm3+ and Yb3+ ions energy capture centers. In bioimaging, the 1532 nm laser exhibits deeper imaging depth due to weak photon scattering and autofluorescence. Furthermore, red light emission has the greatest tissue penetration depth in the visible region. The luminescence intensity and tissue penetration depth of both the excitation and emission light make them suitable for deep tissue imaging. We investigated temperature sensing performance of NaLuF4:20 % Er3+/1 % Tm3+/10 % Yb3+ microcrystals, and found that the maximum relative sensitivity of LIR (I521/I540) reaches 0.92 %K−1. The microcrystals NaLuF4:20 % Er3+/1 % Tm3+/10 % Yb3+ are anticipated to have application in deep tissue imaging and temperature sensing.

Single-crystalline GaN microdisk arrays grown on graphene for flexible micro-LED application

We report the growth of single-crystalline GaN microdisk arrays on graphene and their application in flexible light-emitting diodes (LEDs). Graphene layers were directly grown on c-sapphire substrates using chemical vapor deposition and employed as substrates for GaN growth. Position-controlled GaN microdisks were laterally overgrown on the graphene layers with a micro-patterned SiO2 mask using metal–organic vapor-phase epitaxy. The as-grown GaN microdisks exhibited excellent single crystallinity with a uniform in-plane orientation. Furthermore, we fabricated flexible micro-LEDs by achieving heteroepitaxial growth of n-GaN, In x Ga1−x N/GaN multiple quantum wells, and p-GaN layers on graphene-coated sapphire substrates. The GaN micro-LED arrays were successfully transferred onto bendable substrates and displayed strong blue light emission under room illumination, demonstrating their potential for integration into flexible optoelectronic devices.

The preparation of CuO film under different annealing atmospheres and investigation of the excellent electrical and undoped tunable electroluminescence characteristics of Au/i-CuO/n-GaN LED

Copper oxide (CuO) film is widely used in optoelectronic devices. The CuO films were fabricated by radio frequency (RF) magnetron sputtering and then annealed at 700 °C under different atmospheres (unannealed, O2, N2, vacuum). The physical characteristics of the films were analyzed systematically. In addition, we prepared Au/i-CuO/n-GaN metal-insulator-semiconductor (MIS) structure devices using optimized conditions. The devices had excellent rectifying characteristics at different ambient temperatures and the turn-on voltage was about 1.7 V. The working mechanism of the diode was analyzed through electroluminescence (EL) spectra and band structure. The EL spectra observed at positive and negative bias were compounded by holes and electrons on the gold electrode passing through the insulating layer into the n-GaN side. The EL spectra exhibited that a dominant ultraviolet (UV) emission peak at ∼376 nm was observed under forward bias (FB), and a strong near-white light emission peak at ∼530 nm was observed under reverse bias (RB). The device exhibited unique electroluminescent spectra tunability varying with bias conditions. The chrominance coordinate of the device under RB was (0.3067,0.3604), and the color temperature was 6585 K. This study proved the application potential of i-CuO as an insulating layer in the preparation of new reference for MIS structured GaN-based tunable light-emitting diodes.