White Light-emitting Diodes Research Articles

Fluorescent columnar liquid crystals based on BTD hexacatenars with salicylaldimine and benzaldimine core: Self-assembly and multifunctional properties

Two series of hexacatenars SB/n and BB/n containing a benzothiadiazole (BTD) central core with triple alkyl chains at both ends via salicylaldehyde or benzaldehyde derivated Schiff base links, respectively, were prepared. Different Schiff base links lead to different self-assembly and photophysical behaviors. Both series can self-assemble into columnar liquid crystal (LC) phases but with different lattices (p6mm for SB/n, p4mm for BB/n) in bulk states, and SB/n can additionally form gels in organic solution. Interestingly, SB/n series were characterized with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission enhancement (AIEE) effects, and displayed high fluorescence in their solid, LC and gel states with large Stokes shifts and environmental sensitive unique spectra patterns. The effect of photoisomerization driven by ESIPT process on LC state of SB/n was observed. The applications of SB/n as fingerprint imaging device, Al3+ fluorescence chemosensor, white light emitting diodes (WLED) as well as light-emitting liquid crystal displays (LE-LCD) have been successfully realized.

An investigation for optical, photocatalytic, photoluminescence and dielectric properties of Cd0.40Ni0.60ZnO2 annealed nanocomposites

We report here the optical, photoluminescence (PL), and dielectric properties of Cd0.40Ni0.60ZnO2 nanocomposites annealed between 200 and 600oC. An increase in annealing temperature (Tann) up to 600oC correlates with a gradual increase in the crystallite and particle sizes. The surface area, pore radius, and pore volume are increased as Tann increases from 200oC to 300oC, and then decreased, but still higher than of 200oC. Similar behaviors were obtained for the absorbance carrier density, photocatlytic efficiency, degradation rate, PL intensity, dielectric constant, dielectric loss, ac conductivity, F-factor, series resistance, and electronic polarizability. While the energy gap, binding energy, impedance of grains and their boundaries, and effective capacitance show an opposite behavior. The relaxation times at the peak of dielectric parameters are between 11.54 and 159.24ns and between 35.23 and 24273.73ns, respectively. The Cole-Cole plot shows a single semicircle at Tann < 400oC and two successive semicircles at Tann> 500oC. The energy of PL of visible emissions is independent on the chosen Tann. These findings indicated that the nanocomposite annealed at 300oC can be used for water purification, telecommunications, solar cells, supercapacitor, and white light-emitting diodes (LEDs).

Structural and temperature-dependent photoluminescence properties of NaBaBO3:Ce3+,Tb3+ phosphors synthesized using the combustion method

This study explores the structural and temperature-dependent photoluminescence of Ce3+ and Tb3+ doped NaBaBO3 phosphors, synthesized via combustion. Analysis of their crystal structures confirmed excellent alignment with the standard PDF#98–008-0110. Investigation into both room and low-temperature photoluminescence revealed that the dopants have a significant effect on emission spectra. Ce3+-doped samples exhibited excitation peaks at 275 nm and 358 nm, leading to a primary emission at 419 nm, with enhanced low-temperature emission suggesting reduced non-radiative processes. Tb3+-doped phosphors showed excitation from 250 to 377 nm and emissions from blue to deep red, including strong green emission at 550 nm due to 5D4→7F5 transitions. Optimal doping was found at 1 mol% for Ce3+, while Tb3+ showed increased luminescence up to 3 mol%, with concentration quenching observed beyond these points. The study indicates dipole–dipole interactions dominate Ce3+ concentration quenching, whereas Tb3+ involves both electric dipole and quadrupole interactions. This analysis provides insights into enhancing luminescent efficiency and suggests NaBaBO3:xCe3+,Tb3+ phosphors' potential in advancing white LED technology, highlighting their stable luminescent properties at low temperatures.

High External Quantum Efficiency and Dual-Band Emission of (C7H18N)3Sb2Cl9 for Sensitivity Temperature Sensing.

Organic-inorganic hybrid halides have gained attention for their ease of processing and remarkable optoelectronic properties. However, the relationship between the structure and optical properties requires further exploration. In this study, the butyltrimethylammonium cation (C7H18N+) was chosen, and seven compounds were synthesized: (C7H18N)3Sb2X9 (X = Cl, Br), (C7H18N)3Bi2X9 (X = Cl, Br, I), and (C7H18N)(C2H8N)MBr5 (M = Sb, Bi). Crystals with a single organic cation exhibit a zero-dimensional structure, while the introduction of dimethylamine ions increases the crystal dimensionality from zero-dimensional (C7H18N)3Sb2Br9 to one-dimensional (C7H18N)(C2H8N)SbBr5. Under 372 nm excitation, (C7H18N)3Sb2Cl9 showed broad orange-red single-band emission with a high photoluminescence quantum yield of 88.4% and an external quantum efficiency of up to 56.9%. A white light-emitting diode based on (C7H18N)3Sb2Cl9 achieved a high color rendering index of 96.3. Moreover, dual-band emission was observed in (C7H18N)3Sb2Cl9 under 308 nm excitation, which exhibits an absolute temperature sensitivity of 1.96 × 10-3 K-1 (320 K), and a flexible film was prepared by incorporating polydimethylsiloxane. This shows the promise of hybrid metal halides as photoluminescent materials and their possibilities for temperature sensing.

Influence of light-emitting diodes (LEDs) on the 2,4-diclorophenoxyacetic acid phytoremediation by plectranthus neochilus

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide widely used in crops against broadleaf weeds. However, 2,4-D residues are considered an environmental pollutant in bodies of water. Phytoremediation with Plectranthus neochilus is a substantial strategy to remove 2,4-D from the aquatic environment. The objective of this study was to verify the efficiency of the association of the photostimulus by Light Emitting Diodes (LED) with P. neochilus to improve phytoremediation of 2,4-D in water. Phytoremediation was evaluated with the following samples: natural light, white LED, blue LED, and red LED, with and without the plant as controls. The data corresponding to the validation of the method were in accordance with the required parameters: R2: 0.9926; RSD: 1.74%; LOD: 0.075 mg.L−1; LOQ: 0.227 mg.L−1 and recovery by SPE was 76.57%. The efficiency of the association of LED with P. neochilus in the 28 days was: ambient light + plant (47.0%); white light + plant (37.10%); blue light + plant (26.80%); red light + plant (3.32%). This study demonstrated, for the first time, the efficiency of using LEDs light in association with P. neochilus for the phytoremediation of 2,4-D in water.

Advances in Host-Free White Organic Light-Emitting Diodes Utilizing Thermally Activated Delayed Fluorescence: A Comprehensive Review

Advances in Host-Free White Organic Light-Emitting Diodes Utilizing Thermally Activated Delayed Fluorescence: A Comprehensive Review

Novel single phase warm white-emitting phosphor BaLaGaO4:Dy3+,Sm3+ with high thermal stability and color stability

In this study, new phosphors BaLaGaO4 (BLGO) doped with dysprosium (Dy3+) and samarium (Sm3+) ions were created using a high-temperature solid-state method. Characterizations with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and elemental mapping revealed successful doping and uniform elemental distribution. Then the samples were tested for photoluminescence (PL) spectra, the results indicated that the BaLaGaO4:xDy3+ (BLGO:xDy3+) phosphors emitted strong blue and yellow light upon excitation at 350 nm. The emission peaks were located at 480 and 572 nm, respectively. By introducing different proportions of Sm3+ ions, the BaLaGaO4:0.04Dy3+,ySm3+ (BLGO:0.04Dy3+,ySm3+) samples could be excited at 365 nm, and enhancing the red emission component of the phosphor. Meantime, with increasing Sm3+ content, the correlated color temperature (CCT) decreased from 5507 to 3767 K. And the emission spectrum and decay lifetime of BLGO:0.04Dy3+,ySm3+ confirmed the energy transfer from Dy3+ to Sm3+. Furthermore, at 423 K, the luminous intensity of BLGO:0.04Dy3+,0.04Sm3+ retained 86 % of its strength at 298 K, and the chromaticity shift (ΔS) was only 0.00574, which indicated that the sample had excellent thermal stability and excellent color stability. Finally, using the prepared sample and a 365 nm light-emitting diode (LED) chip, a white light-emitting diode (WLED) was fabricated. The CCT of the manufactured WLED also showed a corresponding reduction (from 3423 to 2814 K). Moreover, under the working conditions of 3.4 V and 0.6A, the thermal imaging obtained after 90 min of WLED operation shows the stability of the packaged WLED at high temperature. These researches show that the phosphor has potential application value in indoor lighting technologies.

Stabilized CsPbBr3 quantum dots in flower-like LYH matrix for high-performance white light-emitting diodes

Stabilized CsPbBr3 quantum dots in flower-like LYH matrix for high-performance white light-emitting diodes

Analysis of Visible Light Communication System with QAM-OFDM Modulated White LEDs using FSO

Analysis of Visible Light Communication System with QAM-OFDM Modulated White LEDs using FSO

Side Connection for High‐Efficiency Organic Photovoltaic Modules for Indoor Applications: Shunt Reduction and Performance Improvement

Indoor photovoltaics has attracted increasing attention because of its potential to power devices of the Internet of Things. The power conversion efficiency (PCE) of organic photovoltaic (OPV) cells has reached values beyond 30% under indoor light, but for OPV modules it is still significantly lower. One reason is that the full width interconnection of sub‐cells in such modules. Here, a new side connection method is presented which significantly reduces shunts and thus improves performance of OPV modules for indoor applications where a large parallel resistance is crucial. To prove its advantage, OPV modules were fabricated on both Indium Tin Oxide (ITO) and ITO‐free substrates. Under 500 lux cool white LED light, the highest PCE of ITO‐free side connection modules (SCMs) is 15.1%, while for conventional full width connection modules (FWCMs) it is 14.4%. For ITO‐based modules under 1000 lux, it is 2.3% for FWCMs compared to 12.1% for SCMs. Thermography images show that the improvement stems indeed from the reduction of shunts. Finally, results from experiments as well as from numerical simulations illustrate clearly that efficiency losses stemming from the increased series resistance for the side connection are rather small and that they are overcompensated by the increased shunt resistance.This article is protected by copyright. All rights reserved.

Dy3+ doped KCa(PO3)3 phosphor for white light generation: structural and luminescent studies

Abstract Using the traditional solid-state reaction approach, Dy3+ ions doped KCa(PO3)3 phosphors have been synthesized to investigate their luminescent properties to produce high-quality white light for solid-state lighting applications, particularly in white LEDs. X-ray diffraction (XRD) patterns were used to examine the structure and phase of the phosphors. Using scanning electron microscopy (SEM), the morphology of the as-synthesized phosphor has been investigated. Fourier transform infrared spectroscopy (FT-IR) has been used to investigate several vibrational bands seen in the phosphor. Using diffuse reflectance spectra (DRS), the as-synthesized phosphors' optical band gap values have been estimated. When Dy3+ ions are excited at 350 nm, the photoluminescence (PL) spectra characteristics observed for the activated KCa(PO3)3 phosphor show strong white area emission at 575 nm, which is related to the 4F99/2 → 6H13/2 transition of Dy3+ ions. Additionally, the concentration quenching of Dy3+ ions doped at 4 mol% is seen in the PL spectra. Based on the observed PL spectra, the computed CIE chromaticity coordinates for the doped KCa(PO3)3 phosphors show that the optimised 4.0mol% Dy3+ doped phosphor is located in the deep white area. The lifespan of the as-titled phosphors decreases as the amount of Dy3+ ions increases in the host lattice. Additionally, the PL decay profiles shows a dual exponential behaviour when excited at 350 nm, with an emission wavelength at 575 nm. On the basis of the results of the aforementioned studies, we wish to project Dy3+ ion doped KCa(PO3)3 phosphors as white light generating materials in w-LEDs and for other photonic applications.

Embedding Te4+ into Sn4+-Based Metal Halide To Passivate Structure Defects for High-Performance Light-Emitting Application.

Low-dimensional lead-halide hybrids are an emerging class of optical functional material but suffer the problems of toxicity and poor air stability. Among lead-free metal halides, tin(IV)-based metal halides are promising optoelectronic materials due to their robust structure and environmental friendliness. However, their photoluminescence (PL) properties are poor, and the underlying mechanisms are still elusive. Herein, a stable Sn4+-based halide hybrid, (C4H7N2)2SnCl6, was developed, which however exhibits poor PL properties at room temperature (RT) due to the lattice defects and the robust crystal structure. To enhance its PL efficiency, the Te4+ ion with a stereoactive 5s2 lone pair has been introduced into the lattice. As a result, Te4+-doped (C4H7N2)2SnCl6 displays broadband orange emission (∼640 nm) with a PL efficiency of ∼46% at RT. Interestingly, Te4+-doped (C4H7N2)2SnCl6 shows triple emission bands at 80 K, which could be due to the synergistic effect of the organic cations and the self-trapped state induced by Te4+. Additionally, high-performance white light-emitting diodes were prepared using Te4+-doped (C4H7N2)2SnCl6, revealing the potential of this material for lighting applications. This study provides new insight into the PL mechanism of Sn4+-based metal-halide hybrids and thus facilitates the design and development of eco-friendly light-emitting metal halides.

Two-dimensional Keitz method for the radiant power measurement of planar ultraviolet excilamps

Planar XeBr∗ and XeCl∗ excilamps emitting noncoherent narrowband UVB light (280–315 nm) are now widely used to cure psoriasis and vitiligo as well as to improve vitamin D synthesis. The two-dimensional integral formula has been deducted in this study, which is a good method and has great practical significance to calculate the total radiant power and assess the energy efficiency of a planar UV lamp. The measured radiant power of planar white LED lamps through a two-dimensional Keitz formula has been compared to that of gonio-photometer, verifying the applicability of the formula. The optimum measurement distance is dependent on the lamp length (1.5L≤D≤3.5L) for which the derivation from the two methods can be controlled within 10%. The planar XeBr∗ excilamps have been measured and compared to coaxial excilamps, which show similar patterns of change for the radiant characteristics. Since the planar radiant power formula only needs to measure normal illuminance at a certain distance from the symmetric center of the lamp, it is more convenient to use and is a low-cost method to promote the development of large-sized planar ultraviolet lamps.

Supramolecular Sequential Light-Harvesting Systems for Constructing White LED Device and Latent Fingerprint Imaging.

The fabrication of supramolecular light-harvesting systems (LHS) with sequential energy transfer is of significance in utilizing light energy. In this study, we report the non-covalent self-assembly of a sequential LHS by pillar[5]arene-based host-guest interaction in water and its applications in white light-emitting diode (LED) device and latent fingerprint imaging. The host-guest complex WP5⸧G self-assembles into nanoparticles in water and shows enhanced aggregation-induced emission (AIE) effect. The nanoparticles can be further used to construct sequential LHS with fluorescent dyes 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (DBT) and sulforhodamine 101 (SR101). Impressively, the system shows white-light emission when the molar ratio of WP5⸧G/DBT/SR101 is 1100/2/16. The material can be coated on a LED bulb to achieve white-light emission. In addition, the sequential LHS exhibit color-tunable fluorescence including red emission, which have been successfully applied to high-resolution imaging of latent fingerprints. Therefore, we demonstrated a general strategy for the construction of sequential LHS in water based on macrocyclic host-guest interaction and explored its multi-functional applications in white-light LED device and imaging of latent fingerprints, which will promote future development and application of supramolecular LHSs.

Flexible, photoluminescent 0D Cs4PbX6 (X = Br, Br/I)–PMMA composite films for white LED via water-induced recrystallization

Abstract3D CsPbX3 inorganic perovskite materials have attracted much attention in optoelectronic devices because of their strong absorbance, high photoluminescent quantum yield, tunable band gap, and narrow emission bandwidth. However, their practical usefulness is limited due to their poor stability in ambient conditions. Here, we created photoluminescent 0D Cs4PbX6 (X = Br, Br/I) suspensions in toluene by adding a small amount of water. The photoluminescent 0D Cs4PbX6 perovskite was mixed with polymethylmethacrylate (PMMA) forming 0D Cs4PbX6/PMMA composite films with higher PL, stability, transparency, and transmittance than that of the 3D CsPbX3/PMMA composite films prepared separately. Moreover, the PL intensity maintains 90% of the initial value after 30 days in water, showing excellent water stability. The flexible white-light LED device prepared by the composite films illustrated good luminescence performance with color rendering index 74.77, chromaticity coordinates (0.32, 0.33), and color temperature 6997 K. Graphical abstract

Optimizing Transport Carrier Free All-Polymer Solar Cells for Indoor Applications: TCAD Simulation under White LED Illumination.

This work inspects the utilization of all-polymer solar cells (APSCs) in indoor applications under LED illumination, with a focus on boosting efficiency through simulation-based design. The study employs a SCAPS TCAD device simulator to investigate the performance of APSCs under white LED illumination at 1000 lux, with a power density of 0.305 mW/cm2. Initially, the simulator is validated against experimental results obtained from a fabricated cell utilizing CD1:PBN-21 as an absorber blend and PEDOT:PSS as a hole transportation layer (HTL), where the initial measured efficiency is 16.75%. The simulation study includes an examination of both inverted and conventional cell structures. In the conventional structure, where no electron transportation layer (ETL) is present, various materials are evaluated for their suitability as the HTL. NiO emerges as the most promising HTL material, demonstrating the potential to achieve an efficiency exceeding 27%. Conversely, in the inverted configuration without an HTL, the study explores different ETL materials to engineer the band alignment at the interface. Among the materials investigated, ZnS emerges as the optimal choice, recording an efficiency of approximately 33%. In order to reveal the efficiency limitations of these devices, the interface and bulk defects are concurrently investigated. The findings of this study underscore the significance of careful material selection and structural design in optimizing the performance of APSCs for indoor applications.

Visible-light-driven BiOI and GO/BiOI photocatalysts for organic pollutants degradation and hydrogen production using low power sources

BiOI and (3 wt%)GO/BiOI visible-light-driven photocatalysts were obtained by a one-pot solvothermal method and successfully applied to the degradation of single and binary dye solutions of rhodamine B (RhB) and methylene blue (MB) and H2 production using very low-power sources. The GO/BiOI with hierarchical flower morphologies exhibited the highest activity, achieving RhB and MB photodegradation percentages (%Xdye) of 100% and 80%, respectively, in 240 min employing a simple 19 W white LED array. Furthermore, GO/BiOI dosage and RhB initial concentration play an essential role in dye degradation, and scavenger assays confirmed that holes and superoxides are the main species causing RhB oxidation. TOC analysis determined an efficiency of 70%, and after three uses, the GO/BiOI attained a %XRhB of 84%. The H2 evolution was performed under 2 W UV light, yielding 323.25 μmol/h∙g of H2 for BiOI, and the addition of GO nanosheets increased the photoactivity of GO/BiOI up to 63% (509.61 μmol/h∙g). The catalytic activity of GO/BiOI is superior to values reported in the literature considering nominal power consumption (kWh) vs. efficiency of RhB degradation or H2 production.

Spectral studies of thermally stable Dy3+/Sm3+ co-doped Li2Ba5W3O15 phosphors for warm white LEDs

In the current study, a series of Li2Ba5W3O15: RE3+ (RE = Dy, Sm) [LBW:Dy3+/Sm3+] phosphors were prepared using a high-temperature solid-state method. X-ray diffraction, Scanning electron microscopy with energy-dispersive x-ray analysis scans showed that the crystal form was consistent with the standard LBW and comprised small irregularly shaped particles. Diffuse reflectance spectral (DRS) data was utilized to calculate the band gaps. Fluorescence study shows that LBW material doped with Dy3+ and Sm3+ yield distinct colors at 496 nm (blue) for Dy3+ and 582 nm (green-yellow), 612 nm (yellow), and 669 nm (red) for Sm3+ when excited by near-ultraviolet (336 nm) light. The observation of energy transfer between Dy3+ and Sm3+ ions play a role in modifying the luminescence of LBW:Dy3+/Sm3+ co-doped phosphors. With a constant excitation wavelength (λ Ex), different levels of activator doping lead to a change in the emission colors from their neutral white light to a deep orange-red region for LBW:Dy3+/Sm3+ phosphors. The decay curves demonstrate a decrease in lifetime with an increase in the concentration of activator ions (Sm3+). For D3S5 phosphor, the temperature-dependent photoluminescence characteristics were analyzed under λ Ex = 336 nm excitation. The results indicate excellent luminescence thermal stability with an activation energy of 0.16 eV at λ Ex = 336 nm. With its low color-correlated temperature and good thermal stability, the prepared phosphor sample shows potential as a solid-state emitting phosphor that can be used with UV chip stimulation for warm white LED applications.

Stable solvatochromic light-emitting diodes and their potential for color temperature adjustment of white LEDs

A viable technology for liquid phosphor-based light-emitting diodes (LEDs) with emission color tuneability is described. These devices are based on Tris(bipyridine)ruthenium(II) chloride but can be constructed from other similar metal coordination charge transfer complexes. The Frank-Condon excited state generated upon the absorption of blue (450 nm) pump photons has a large electric dipole moment due to intramolecular metal-to-ligand charge transfer from the ruthenium atom to one specific bipyridyl ligand. Polar solvents respond to the dipole field creating a solvatochromic shift that is solvent dependent. The devices were fully sealed in either a long path length or a short path length configuration. The latter encapsulating the luminescing medium in hollow silica spheres that can be easily applied like a slurry on top of InGaN/GaN LED dies. The devices were optically, thermally and environmentally stable. Also discussed is the possibility of using solvatochromic emitters for achieving color temperature tuneability in white LEDs.

White Light Emissive Eu(III) Complexes through Ligand Engineering and their Applications in Cool Near Ultraviolet White Light Emitting Diodes and Thermometer.

In pursuit of enhancing white light quality for SSLapplications, an attempt has been made to design novel imidazo-bipyridyl ligands as an ancillary ligand to obtain multiple emissions (mimic sunlight) in the Eu-complex. By strategically modifying the phenanthroline core with imidazo-bipyridyl incorporation with 1 or 2-Napthyl groups at the C1 position, the excitation spectral line is successfully shifted from Ultraviolet (UV) to near UV/visible spectrum (where the LED emission occurs). The ligands showed greenish blue emission in solid and solution. The analysis revealed that the energy transfer is incomplete, primarily attributed to the proximity of triplet state energy levels to the resonance level of Eu(III) ions as reflected in solvatochromism. These complexes exhibit a unique dual emissive behavior (emitting multi-color) including white light across various solvents. The fabricated white LED showed an excellent color rendering index (CRI ~93 %). Beyond lighting, this distinctive property opens avenues for temperature sensing ([Eu(DBM)31-Naph] shows the highest sensitivity of Sr = 10.97 %, and [Eu(DBM)32-Naph] shows the highest sensitivity of Sr = 5.5 % at 333K) and vapoluminescent studies. This research pioneers the development of these complexes as potential single-component materials for white LEDs, underlining their multifaceted utility in cutting-edge lighting and sensing technologies.