Application In Light-emitting Diodes Research Articles

The effect of Al3+ ions on the self-reduction process of Yb3+ to Yb2+ ions and optical properties of Nd3+/Ybn+ (n = 3, 2) co-doped transparent silicate glass-ceramics containing Ba2LaF7 nanocrystals and Ag nanoparticles

The effect of Al3+ ions in the AlF3 compound on the reduction process of Yb3+ to Yb2+ ions in SiO2–AlF3–BaF2–TiO2–LaF3 (SABTL) transparent silicate glass-ceramics was investigated. The valence states of the elements in the raw materials mixture existing in the transparent silicate glass-ceramics were determined using X-ray photoelectron spectroscopy (XPS) spectrum analysis. The transparent silicate glass-ceramics SABTL containing Ba2LaF7 nanocrystals and Silver (Ag) nanoparticles (AgNPs) were identified through X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) image. With the increase of Al3+ ions molar concentration, the self-reduction process of Yb3+ to Yb2+ ions was enhanced and thus significantly affected the optical bandgaps and upconversion (UC)-, near-infrared (NIR)- emissions of Nd3+/Yb3+ co-doped in SABTL containing Ba2LaF7 nanocrystals and AgNPs under excitation of 980 nm laser diode (LD). The optimal molar concentration ratio between SiO2 and AlF3 compound was determined such that the NIR bandwidth flatness of Nd3+/Yb3+ co-doped in SABTL containing Ba2LaF7 nanocrystals in the wavelength range of 1000–1200 nm was the flattest. In addition, the CIE 1931 (x, y) color coordinates for UC- and visible (VIS)- emissions of Nd3+/Yb3+ co-doped SABTL-0.5Nd2Yb-xAg (x = 0, 2, 3, 4, and 5) glass-ceramics samples are also calculated and determined the color region for light-emitting diode (LED) application.

SM3+-Activated LiZnPO4 Phosphors: Synthesis, Characterization, and Their Luminescent Properties for White Light-Emitting Diode Applications

SM3+-Activated LiZnPO4 Phosphors: Synthesis, Characterization, and Their Luminescent Properties for White Light-Emitting Diode Applications

Non-monotonic thermal conductivity modulation in colloidal quantum dot superlattices via ligand engineering

Colloidal quantum dots (QDs), which consist of inorganic cores surrounded by soft organic ligands, can self-assemble into superlattices exhibiting long-range order. Their tunability, in terms of size, shape, and ligand properties, makes them promising for applications in solar cells, photodetectors, and light-emitting diodes. However, the complex interplay between ligand stiffness, QDs cores-ligands coupling strength, and its impact on QDs' morphology and thermal properties is not well understood. This work employs molecular dynamics simulations to investigate the possibility of modulating the thermal conductivity of QDs superlattices via ligand engineering. It is found that the structural stability of QDs superlattices depends significantly on the interaction strength between the QDs cores and ligands. At lower interaction strengths, the instability manifests itself in a random fusion of the QDs cores, while at intermediate strengths a stable simple cubic lattice structure is maintained. Higher interaction strengths lead to amorphization in the surface regions of QDs core. We observed a nonlinear trend in the thermal conductivity with varying QD-ligand interaction strengths due to competing factors: fusion of QDs cores at lower interaction strengths and increased crosslinking interaction among ligands at higher interaction strengths. The influence of ligand stiffness on thermal conductivity was found to be minimal. This study provides a deep insight into the role of ligand stiffness and interaction strength on structural dynamics and thermal transport in QDs superlattice and demonstrates the feasibility of engineering thermal transport in QDs superlattice via ligand engineering.

Charge compensation improves energy transfer to realize anti-thermal-quenching and enhances the CaMoO4: Sm3+ phosphors optical temperature measurement sensitivity base on the FIR model

Luminescent materials are the main focus of non-contact thermometers due to their high detection sensitivity, non-invasiveness, quick reaction, exceptional stability. It is still difficult to design high sensitivity optical temperature sensors using fluorescence intensity ratio technology. This article increases fluorescence intensity ratio value and obtains high sensitivity temperature sensitive phosphors by utilizing the anti-thermal-quenching effect of rare earth luminous centers. Sm3+ and alkali metal co-doped CaMoO4 phosphors have been prepared by high-temperature solid-state method. Rietveld refinement results showed that the co-doping of Sm3+ and K+ can significantly improve the energy transfer from the host to Sm3+ and significantly increase the luminous intensity of Sm3+. We found that co-doping of Sm3+ and K+ not only effectively enhanced the luminescence intensity, but also regulated the lifetime of this phosphors. When K+ is introduced into the CaMoO4: 0.02Sm3+, the τ value decreased from 4.12 to 3.54 ms, which proves to be effective in light-emitting diode. The optical temperature measurement of CaMoO4: 0.001Sm3+, 0.001 K+ was studied using fluorescence intensity ratio technology. The maximum SaMAX and SrMAX values are 0.27 K−1 at 483 K and 2.25 % K−1 at 363 K, respectively. Moreover, the CaMoO4: 0.02Sm3+, 0.02 K+ also has a certain absorption capacity in visible optical drive, which proved by ultraviolet visible diffused reflectance spectra. The electronic density of states of phosphors are drawn via first-principles to understand the effect of Sm3+ and alkali metals co-doped on luminescence. The above results demonstrate that the Sm3+ and K+ co-doping CaMoO4 might be an attractive material for the application of temperature measurement and light-emitting diode.

Formation of homogeneous pyridinic emission states in carbon dots via solid-state carbonization of aminoquinoline: Optical design principles and light-emitting diode applications

Developing carbon dots (CDs) for practical applications faces significant hurdles due to non-homogeneity in their chemical structure, leading to broad spectral distribution and the excitation-energy-dependent behavior of their fluorescence (FL) emission properties. To address this challenge, we implemented solid-state carbonization of 6-aminoquinoline (6-AQ) devoid of any additives that could induce chemical non-homogeneity. This process yielded pyridinic-nitrogen-doped CDs (PN-CDs) characterized by homogenous, uniform emission states arising from pyridine-incorporated heteroatomic structures. Notably, these PN-CDs exhibited excitation-energy-independent FL at 520 nm with a full-width-half-maximum of 70 nm. To elucidate the structure-property relationship in PN-CDs, a comprehensive analysis encompassing time-resolved spectroscopy and ab initio calculations was conducted. Furthermore, we performed a comparative study by manipulating synthesis parameters and utilizing six AQ isomers, offering valuable insights to optimize the optical properties of PN-CDs. Finally, we successfully demonstrated high-color-purity and efficient green light-emitting diodes utilizing PN-CDs, highlighting their potential for future display applications. This paves the way for advancement in optical materials with enhanced performance and reduced environmental impact.

Spectrum regulation of LuAG:Ce phosphor ceramic with Gd doping for high-brightness and high-power yellow-emitting LEDs applications

To realize the high-brightness of yellow light-emitting diodes (LEDs), the yellow-emitting phosphor ceramics with high luminous efficiency (LE) are urgently explored. Based on the idea of spectrum regulation, the Lu3-x-yGdyAl5O12:xCe3+ (LuGdAG:Ce) phosphor ceramics were prepared via vacuum solid-state sintering. The effect of Gd3+ and Ce3+ content on the structure, luminescence and thermal properties of LuAG:Ce ceramics were investigated. The distortion ratio (D) of CeO8 and bandgap were effectively modified via Gd3+ doping, resulting in massive red-shifting of Ce3+ emission (513→561 nm). The LEDs lighting encapsulated by LuGdAG:Ce ceramics changes from green to yellow. Importantly, the yellow LEDs with a LE up to 139.0 lm/W@180 W and a warm correlated color temperature (CCT) of 3620 K were achieved based ceramic Ce07Gd9. The LuGdAG:Ce phosphor ceramic has the best of luminescence performance in phosphor-converted yellow LEDs lighting so far, which is considered to be the highly promising color converter.

From monomer to polymer: Controlled synthesis and comprehensive analysis of poly(p-phenylene vinylene) via ROMP

This study focuses on synthesis and evaluation of [2.2] paracyclophane-1,9-diene to produce a soluble poly(p-phenylenevinylene) (PPV) derivative homopolymer using ring-opening metathesis polymerization (ROMP). The resulting homopolymer displayed a narrow polydispersity index (PDI) of 1.22, indicating precise control over polymerization. The PPV derivative exhibited excellent solubility in various organic solvents. Photophysical properties, including optical absorption and fluorescence emission spectra, were investigated to evaluate utilization in optoelectronic devices. Optical band gaps ranged from 2.21 to 2.25 eV for thin films and 2.07 to 2.19 eV for solutions, while the electrochemical band gap, determined by cyclic voltammetry, was 2.37 eV. These materials demonstrated promising fluorescence activity in various solvents and thin films, suggesting potential applications in organic light-emitting diodes (OLEDs) and related optoelectronic devices.

Efficient non-doped cluster light-emitting diodes based on semiconducting copper iodide hybrids

Copper iodide hybrid clusters have attracted lots of interest in solution-processed light-emitting diodes (LEDs) for solid-state lighting and display in recent years, benefiting from their simple synthesis, structural diversity, high photoluminescence quantum yield (PLQY), and non-toxicity. However, most efficient copper iodide cluster LEDs are made by host-guest doped emitters and thus suffer from cumbersome synthesis and increased costs from the expensive hosts. Here, we report a non-doped cluster LED based on a novel copper iodine hybrid [35DPPy]4Cu2I2 (35DPPy: 3,5-diphenylpyridine) with high PLQY and decent charge transport characteristic. The non-doped [35DPPy]4Cu2I2 film synthesized by a one-step spin-coating approach possess the flat and compact morphology, high PLQY of 59.6%, and excellent heat/ultraviolet (UV) light/moisture/oxygen stability. The efficient green PL of [35DPPy]4Cu2I2 is proved to originate from the synergistic contribution from thermally activated delayed fluorescence and phosphorescence. A non-doped green LED based on [35DPPy]4Cu2I2 emitters is fabricated, achieving a peak external quantum efficiency of 4.8% and a maximum luminance of 3895 cd/m2. More importantly, large-area LEDs with an emitting area of 4.00 cm2 are realized with homogeneous and bright electroluminescence, showing their attractive potentials as novel electroluminescent emitters in the application of non-doped cluster LEDs.

Tetravalent manganese-doped lithium meta-silicate red-emitting phosphors for LED applications: structural and luminescence properties

In this paper, different concentrations of tetravalent manganese-activated lithium meta-silicate red-emitting phosphors, namely Li2SiO3:xMn4+ (x = 0.01, 0.02, 0.03, 0.04 and 0.05 mol), have been prepared by the solid-state reaction method at 950 °C. The structural, thermal, morphological, and optical properties of the sintered phosphors were characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), raman, UV-Visible and photoluminescence (PL) spectra. Excitation and emission spectra are used to study optical characteristics, which match well with the commercially visible region. The red emission bands for Li2SiO3:0.02Mn4+ peak at approximately 642 nm (λex = 425 nm) and 717 nm (λex = 475 nm), respectively due to the spin-forbidden 2E → 4A2 transition. The doping concentrations of xMn4+ in the Li2SiO3 host were investigated, and the correlations between Mn4+ doping concentration and luminescence intensity were examined. The Commission Internationale de l'Eclairage (CIE) chromatic coordinate graph confirmed the emission color observation in the red region, showed an excellent color purity (CP). In addition, the quantum efficiency (QE) of Li2SiO3:Mn4+ phosphors reached up to 70.51%. The investigation shows that synthesized Li2SiO3:Mn4+ phosphors are beneficial for red Light-Emitting Diodes (LEDs) used in solid-state lighting.

Highly luminescent and stable CsPbBr3 perovskite nanocrystals coated with polyethersulfone for white light-emitting diode applications.

Simultaneously improving the stability and photoluminescence quantum yield (PLQY) of all inorganic perovskite nanocrystals (NCs) is crucial for their practical utilization in various optoelectronic devices. Here, CsPbBr3 NCs coated with polyethersulfone (PES) were prepared via an in-situ co-precipitation method. The sulfone groups in PES bind to undercoordinated lead ion (Pb2+) on the CsPbBr3 NCs, resulting in significant reduction of surface defects, thus enhancing the PLQY from 74.2% to 88.3%. Meanwhile, the PES-coated NCs exhibit high water resistance and excellent heat and light stability, maintaining over 85% of the initial PL intensity under thermal aging (70°C, 4h) and continuous 365 nm ultraviolet (UV) light irradiation (24 W, 8h) conditions. By contrast, the PL intensity of the control NCs dramatically dropped to less than 40%. Finally, a diode emitting bright white light was fabricated utilizing the PES-coated CsPbBr3 NCs, which exhibits a color gamut of ~110% NTSC standard.

Optical property dataset of inorganic phosphor

Developing inorganic phosphor with desired properties for light-emitting diode application has traditionally relied on time-consuming and labor-intensive material development processes. Moreover, the results of material development research depend significantly on individual researchers’ intuition and experience. Thus, to improve the efficiency and reliability of materials discovery, machine learning has been widely applied to various materials science applications in recent years. However, the prediction capabilities of machine learning methods fundamentally depend on the quality of the training datasets. In this work, we constructed a high-quality and reliable dataset that contains experimentally validated inorganic phosphors and their optical properties, sourced from the literature on inorganic phosphors. Our dataset includes 3952 combinations of 21 dopant elements in 2238 host materials from 553 articles. The dataset provides material information, optical properties, measurement conditions for inorganic phosphors, and meta-information. Among the preliminary machine learning results, the essential properties of inorganic phosphors, such as maximum Photoluminescence (PL) emission wavelength and PL decay time, show overall satisfactory prediction performance with coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^2$$\\end{document}) scores of 0.7 or more. We also confirmed that the measurement conditions significantly improved prediction performance.

Tunable electronic and optical properties of BAs/WTe2 heterostructure for theoretical photoelectric device design

The geometric structure of the BAs/WTe2 heterojunction was scrutinized by employing ab initio calculations grounded on density functional theory. Multiple configurations are constructed to determine the equilibrium state of the heterojunction with optimal stability. The results show that the H1-type heterojunction with interlayer distance of 3.92 Å exhibits exceptional stability and showcases a conventional Type-II band alignment, accompanied by a direct band gap measuring 0.33 eV. By applying external electric field and introducing strain, one can efficaciously modulate both the band gap and the quantity of charge transfer in the heterojunction, accompanied by the transition of band alignment from Type-II to Type-I, which makes it expected to achieve broader applications in light-emitting diodes, laser detectors and other fields. Ultimately, the heterojunction undergoes a transformation from a semiconducting to a metallic state. Furthermore, the outstanding optical characteristics inherent to each of the two monolayers are preserved, the BAs/WTe2 heterojunction also serves to enhance the absorption coefficient and spectral range of the material, particularly within the ultraviolet spectrum. It merits emphasis that the optical properties of the BAs/WTe2 heterojunction are capable of modification through the imposition of external electric fields and mechanical strains, which will expand its applicability and potential for future progression within the domains of nanodevices and optoelectronic apparatus.

Suppressing nonradiative recombination enables highly efficient red perovskite light-emitting diodes

Quasi-two-dimensional perovskites are promising emitters for red light-emitting diodes. However, the practical application of red perovskite light-emitting diodes (PeLEDs) is still limited by the defect-induced nonradiative recombination. In this study, we demonstrate efficient red PeLEDs by introducing the diethylene glycol bis(3-aminopropyl) ether (DGBE) additive. The coupling effect between oxygen (O) atoms in DGBE and unsaturated Pb2+ not only regulates crystallization, but also passivates defects. Benefiting from the reduced defect densities and enhanced radiative recombination efficiencies, the photoluminescence quantum yield (PLQY) increases from 39 % to 80 %. Consequently, we achieve high-performance red PeLEDs with a maximum external quantum efficiency of 24.2 %, which provides a reliable approach to promote the development of highly efficient red PeLEDs.

Ultrafast spin-flip exciton conversion and narrowband sky-blue luminescence in a fused polycyclic selenaborin emitter.

Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho[3,2,1-de]anthracene (SeBSe) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet-triplet energy gap (ΔE ST) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in SeBSe by virtue of the heavy-atom effect of selenium atoms. Consequently, SeBSe allows ultrafast spin-flip RISC with the rate constant surpassing 108 s-1, which far exceeds the corresponding fluorescence radiative decay rate (∼106 s-1), enabling an ideal singlet-triplet superimposed excited state.

First-principles study on structural, electronic, and optical properties of mixed alloys of Cs2Ag(SbxBi1−x)Br6 double perovskites for optoelectronic applications

Halide perovskites have attracted promising capabilities of solar cells and light-emitting diode applications due to their high stability and optoelectronics performance. In this work, the effect of chemical substitution on the structural, electronics, and optical properties of mixed alloy Cs2Ag(SbxBi1-x)Br6 perovskites (when x is a mixing ratio varying from 0.0 to 1.0) was explored by using the virtual crystal approximation within the first-principle framework based on DFT-GGA, GGA-TB09, RPA, and BSE. Calculation results reveal that the lattice constant increases linearly as a function of the mixing ratio of a(x) = 11.246–0.0012x Å. These results satisfied the Vegard’s law as well as the reliability of virtual crystal approximation. The band structure calculated with and without the spin–orbit coupling was compared. Band gap of the mixed alloys are lower than that of pure Sb or pure Bi compounds. The band gap increases as a quadratic function of Eg = 2.07 – 0.279x – 0.121x2 eV. The smaller band gap of the mixed alloy results from the energy mismatch between Sb and Bb s and p orbitals. Calculations from DFT-TB09 are in good agreement with experimental results. Blue-shifted absorption spectra to the ultraviolet region were found when the Sb content increased. A linear increase of the static dielectric constant was found when the Sb content increased as a function of εs(x) = 2.849 + 0.266x. BSE@PBEsol calculations are consistent with experimental profiles. Calculation results indicate that the mixed alloy Cs2Ag(SbxBi1-x)Br6 can be tuned regarding its electronic and optical properties.

Extended Conjugation Strategy Enabling Red-Shifted and Efficient Emission of Orange-Red Thermally Activated Delayed Fluorescence Materials.

In account of the energy gap law, the development of efficient narrow-band gap thermally activated delayed fluorescence (TADF) materials remains a major challenge for the application of organic light-emitting diodes (OLEDs). The orange-red TADF materials are commonly designed with either large π-conjugated systems or strong intramolecular donor-acceptor (D-A) interactions for red-shift emission and small singlet-triplet energy gap (ΔEST). There are rare reports on the simultaneous incorporation of these two strategies on the same material systems. Herein, two orange-red emitters named 1P2D-BP and 2P2D-DQ have been designed by extending the conjugation degree of the center acceptor DQ and increasing the number distribution of the peripheral donor PXZ units, respectively. The emission peak of 1P2D-BP is red-shifted to 615 nm compared to 580 nm for 2P2D-DQ, revealing the pronounced effect of the conjugation extension on the emission band gap. In addition, the distorted molecular structure yields a small ΔEST of 0.02 eV, favoring the acquisition of a high exciton utilization through an efficient reverse intersystem crossing process. As a result, orange-red OLEDs with both 1P2D-BP and 2P2D-DQ have achieved an external quantum efficiency (EQE) of more than 17%. In addition, the efficient white OLED based on 1P2D-BP is realized through precise exciton assignment and energy transport modulation, showing an EQE of 23.6% and a color rendering index of 82. The present work provides an important reference for the design of high-efficiency narrow-band gap materials in the field of solid-state lighting.

Enhancing light output of WSLED with microlens array fabricated on Tb³⁺/Sm³⁺ co-doped fluorophosphate glass via hot embossing

In this study, Tb3+/Sm3+ co-doped NaPO3–BaF2–AlF3–CaF2 glasses were synthesized using the melt quenching method. These glasses exhibit a glass transition temperature below 380 °C and maintain optical transparency close to 90% within the visible spectrum. Furthermore, under UV excitation, the emission shows a wide spectrum and varies with the rare-earth doping ratio or excitation wavelength. Hence, this glass was introduced into the wide-spectrum light-emitting diode (WSLED) application. Moreover, a microlens array was fabricated on the glass surface using the hot embossing technique. In fact, the microlens array enhanced the light output power of the WSLED by 5% at a driving current of 150 mA.

One-Step Extrusion Preparation for Low-Cost Multicolored Carbon Dot Fluorescent Films.

Carbon dots (CDs), an emerging class of environmentally friendly luminescent materials, have been extensively applied in full-color display of light-emitting diodes (LEDs). However, the synthesis of CDs usually requires high pressure, and the conventional preparation of CD-based LED films involves intricate manufacturing techniques. The resulting security risk and high cost restrict the further application of CD-based LEDs. Here, we present a cost-effective method to obtain CD-based LED films via in situ extrusion in a twin-screw extruder. By fine-tuning the extrusion temperature, we created blue-emitting LEDs. The resulting fluorescent films exhibited remarkable stability, retaining 94% fluorescence intensity after 180 days of storage. We also prepared yellow, pure white, and cool white LEDs with malleable shapes, validating the versatility of the in situ extrusion method. More importantly, the manufacturing cost for CD-based films amounts to only about 0.8 RMB/g, which is substantially lower than that of the reported preparation methods. This work offers a cost-effective, safe, and massive approach to preparing photoluminescent LEDs, paving the way for the development of more sustainable and efficient CD-based LEDs.

Effect of annealing temperature and doping concentrations on structure and optical properties of Eu3+-doped TiO2 nanomaterials

In this study, we successfully synthesized europium-doped TiO2 (TiO2:Eu3+) nanomaterials (NMs) with crystalline sizes ranging from 6.5 to 71.7 nm through a sol-gel method. Analysis of X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra indicates that the substitution of smaller-sized Ti4+ ions (0.745 Å) by larger-sized Eu3+ ions (0.947 Å) was more efficient at higher doping concentrations and annealing temperatures. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the synthesized TiO2:7%Eu3+NMs exhibit a strong red emission band peaking at 613 nm and remarkable absorption in the blue light region centered at 463 nm, making them suitable for use in white light-emitting diode (WLED) applications. Our findings reveal that both annealing temperature and doping concentration significantly influence the structure and properties of these materials. Besides, the research team has seen, under the experimental conditions, the TiO2:7%Eu3+ sample annealed at 800°C exhibits the highest PL intensity. These results underscore the potential of the synthesized TiO2:Eu3+ NMs as red-emitting materials for WLED applications.

Low-temperature photoluminescence characteristic of Tm-doped Ga2O3 films for light emitting diodes application

Tm-doped Ga2O3 films hold significant promise for application in light-emitting diodes (LEDs). A comprehensive understanding of their photoluminescence properties is pivotal for unlocking their full potential. In this work, we present findings on the photoluminescence (PL) spectra of Tm-doped Ga2O3 films, elucidating variations at different measurement temperatures and excitation energies utilizing synchrotron radiation light. The intensity of ultraviolet light (UVL1 and UVL2) exhibits a temperature dependence and its activation energy illustrates an ionization energy of shallow donor and migration through tunneling of self-trapped holes to triply ionized Ga vacancy (VGa) centers forming doubly ionized VGa acceptors. Additionally, the excitation energy-dependent PL spectra provide insights into the excitation mechanism of Tm ions, indicating a most likely through defects in the Ga2O3 host.