White Light-emitting Diodes Research Articles

Synthesis of Good Solid‐State Emissive Carbon Dots through Microwave‐Assisted Microemulsion Process

AbstractEnvironmental‐friendly carbon dots (CDs) have found wide applications in the fields of white light emitting diode (WLED), chemical sensor, wide‐gamut display, etc. However, for the aggregation‐caused quenching (ACQ) effect, high dose of CDs immobilization generally suffers from the great fluorescence quenching, hindering their practical uses in many cases. In the present work, a one‐step microwave‐assisted microemulsion process is developed to prepare matrix‐free green CDs powders with absolute fluorescent quantum yield (QY) up to 48.34%. From dilute solution to matrix‐free powder, the QY of CDs decreases only about 20%, significant smaller than the sample prepared without surfactant (74%). Structural characterization and fluorescent lifetime measurements suggest that the passivation of hydrophobic long‐alkyl chains from surfactant Span‐80 is very key for their good solid‐state photoluminescence (PL). For the good solid‐state PL and various solvent‐compatibility, the CDs reported show promising applications in the fabrication of WLED and the measurement of water content of ethanol/water solution. This work provides a new idea to design and simply synthesize desirable CDs‐based luminescent materials with good solid‐state PL.

Analysis of the effects of various light spectra on microgreen species

ABSTRACT Light conditions, such as spectral composition, intensity and photoperiod, can affect the photosynthetic apparatus and content of beneficial bioactive compounds. The experiments realised under randomised experimental design tested seedlings of 21 genotypes, including 12 genotypes of the Brassicaceae family, lettuce, amaranth, onion, spinach, fenugreek and two beet and two basil genotypes, which were cultivated in three light environments under narrow-band red and blue light-emitting diodes (LEDs) and broad-band white LEDs. Responsiveness to light spectra was assessed based on fresh and dry weight, total chlorophyll and carotenoid contents and non-invasive assessment of specific compounds using fluorescence excitation ratios. In white light, we observed a higher fresh weight compared to that in monochromatic environments, especially compared to blue light. In most of the species, blue and white light had a positive effect on the concentration of chlorophyll and carotene in plants compared to red light. Blue light was associated with the highest values of chlorophyll excitation ratios, indicating a significant increase in flavonoids and anthocyanin contents. Individual microgreens responded differently in all assessed traits, especially in fluorescence ratios. We also observed the clustering of microgreens with similar responses to LED light spectra. In conclusion, in most plant species, multispectral white LEDs positively influenced quantitative and qualitative traits compared to the most frequently used red LEDs. Blue light slightly improved quality, but suppressed growth. Nevertheless, some species responded differently, emphasising the need to optimise the light to improve the microgreens’ production and nutritional value.

Improvement of Bioactive Polyphenol Accumulation in Callus of Salvia atropatana Bunge.

Callus cultures of the Iranian medicinal plant Salvia atropatana were initiated from three-week-old seedlings on Murashige and Skoog (MS) medium supplemented with α-naphthaleneacetic acid (NAA) and various cytokinins. Although all tested hormonal variants of the medium and explant enabled callus induction, the most promising growth was noted for N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU)-induced calli. Three lines obtained on this medium (cotyledon line-CL, hypocotyl line-HL, and root line-RL) were preselected for further studies. Phenolic compounds in the callus tissues were identified using UPLC-MS (ultra-performance liquid chromatography-mass spectrometry) and quantified with HPLC (high-performance liquid chromatography). All lines exhibited intensive growth and contained twelve phenolic acid derivatives, with rosmarinic acid predominating. The cotyledon-derived callus line displayed the highest growth index values and polyphenol content; this was exposed to different light-emitting diodes (LED) for improving biomass accumulation and secondary metabolite yield. Under LED treatments, all callus lines exhibited enhanced RA and total phenolic content compared to fluorescent light, with the highest levels observed for white (48.5-50.2 mg/g dry weight) and blue (51.4-53.9 mg/g dry weight) LEDs. The selected callus demonstrated strong antioxidant potential in vitro based on the 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power (FRAP) tests. Our findings confirm that the S. atropatana callus system is suitable for enhanced rosmarinic acid production; the selected optimized culture provide high-quality plant-derived products.

Cs2MnCl4:Eu2+: A Near-Violet Light-Triggered Single-Component White Light Emitter.

Single-component white-light luminescent materials are considered an economical and facile choice for phosphor-converted white light-emitting diodes (pc-WLEDs). Here, a new single-component white-light-emitting material Cs2MnCl4:Eu2+ based on the combination of a lead-free halide structure and a rare-earth ion is first reported. Benefiting from the smart dilution-sensitization design strategy, white light composed of dual broad emission originating from Eu2+ (blue light, 444 nm, 4f65d1 → 4f7) and Mn2+ (yellow light, 566 nm, 4T1g → 6A1g) was successfully realized under near-ultraviolet light (404 nm) radiation with a high photoluminescence quantum yield of 66%. Based on the single-source Cs2MnCl4:Eu2+ phosphor, a pc-WLEDs device with "eye-friendly" white light production was successfully fabricated. The pc-WLEDs exhibit suitable color coordinates of (0.3294, 0.2746) and a high color rendering index of 82.3, demonstrating the potential in the future health-conscious illumination application by reducing the risk of eye strain and high-energy blue-light damage. This work achieves a new single-component white-light-emitting Mn-based halide phosphor and provides a new path for the design of single-component white light sources in Mn-based halides.

Facile synthesis of rare earth ions doped LiSr4(BN2)3 phosphors for white light-emitting diodes

Rare earth ions doped nitride is a kind of excellent phosphor for phosphor-converted white light-emitting diodes (WLEDs). However, the critical synthesis condition limits the application of nitrides in WLEDs. In this work, we develop a modified carbothermal reduction and nitridation method to synthesize rare earth ions doped LiSr4(BN2)3 phosphors. The crystal structure, morphology and photoluminescence properties of the obtained phosphors were systematically investigated. Intense blue emitting is achieved in Ce3+ doped LSBN with internal quantum efficiency (IQE) of 85.7 % and external quantum efficiency (EQE) of 45.5 %. The emitting color can be tuned from blue to green by co-doping with different amounts of Tb3+ ions. Near unit IQE is achieved in LSBN:Ce 0.5 mol%, Tb 5 mol%. The obtained phosphors exhibit excellent thermal and color stability at temperature range of 300–523 K. A WLED is fabricated by coating LSBN:Ce 0.5 mol%, Tb 5 mol% and commercial CaAlSiN3:Eu2+ on a 370-nm chip. The rare earth ions doped LSBN phosphors with high QE and excellent thermal stability in this work are promising candidates for WLEDs

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).

Single-phase Ca3Sc2Ge3O12: Tb3+, Eu3+ phosphors with tunable photoluminescence and temperature sensing properties

A set of germanate garnet phosphors containing Tb3+ and Eu3+ were adequately synthesized using the high-temperature solid-state technique. The structural properties, photoluminescence characteristics, fluorescence lifetimes, and temperature-sensing capabilities of the phosphors were thoroughly investigated. X-ray diffraction confirms the crystalline structure of the phosphors, while photoluminescence spectra reveal a colour shift attributed to the transfer of energy from Tb3+ to Eu3+ as the concentration of Eu3+ increases. The phosphors excited by UV light display a transition in colour from green to yellow, and subsequently to red, which can be used as a colour tunable phosphor in white light-emitting diode (w-LED) applications. As a novel temperature sensing material, the maximum relative sensitivity of Ca3Sc2Ge3O12: Tb3+, Eu3+ phosphor is 0.1044 K–1 (298 K), highlighting its potential for applications in temperature sensing.

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.

Extended π-conjugated systems by external ligand-assisted C−H olefination of heterocycles: Facile access to single-molecular white-light-emitting and NIR fluorescence materials

The design and synthesis of a novel π-conjugated fluorescent framework by external ligand-assisted C−H olefination of heterocycles with excellent regioselectivity and broad substrate scope are reported herein. These novel fluorescent materials could present full-color-tunable emissions with large Stokes shifts. Furthermore, the protocol provides an opportunity to rapidly screen novel organic single-molecule white-light materials with high fluorescence quantum yields. The robust organic and low-cost white light-emitting diodes could rapidly be fabricated using the white-light-emitting material. Experimental data and theoretical calculations indicate that in the white-light dual emission the relatively short wavelength from high-lying singlet state emission and the relatively long wavelength from low-lying singlet state emission. The anti-Kasha dual-emission systems will provide a foundation for the development and application of organic single-molecule white light materials, effectively promoting the development and innovation of luminescent materials. In addition, this method demonstrated its potential application in the synthesis of new near-infrared (NIR) fluorescence materials with large Stokes shifts based on the olefination of heterocycles.

Low-Dimensional Perovskite in Acrylic Monomers for Underwater White LED

Low-Dimensional Perovskite in Acrylic Monomers for Underwater White LED

65‐4: Patterned Glass Diffusers (PGDs) for Automotive White LED Backlights

Patterned glass diffusers (PGDs) have been demonstrated to reduce backlight thickness and LED count, and increase luminance when used with an optimal film stack in blue mini‐LED backlights. However, they encounter challenges when used in automotive white LED backlights. We report our PGD solution to dimensionally and thermally stable automotive white LED backlight that has an LED pitch of 13 mm.

Novel color-tunable K3Y(BO3)2:RE3+ (RE = Tb3+, Eu3+, Tb3+/Eu3+) phosphors for near-UV white LEDs

Novel color-tunable K3Y(BO3)2:RE3+ (RE = Tb3+, Eu3+, Tb3+/Eu3+) phosphors for near-UV white LEDs

Influence of annealing temperature and laser irradiation on the structural, optical, and photoluminescence characteristics of Ni2O3/SnO2 nanocomposites for perspective applications

In this study, a new approach methodology is employed to modify the structural, optical, and photoluminescence properties of Ni2O3/SnO2(NO/TO) nanocomposites. The effects of temperature and laser irradiation on a specific system were analyzed and described using XRD, XPS, and TEM. The diffraction patterns indicate the presence of two distinct phases within the NO/TO system. The XPS results reveal a robust underlying interaction between Ni2O3 and SnO2, exhibited by the observed shifts in the peak positions of Ni 2p, Sn 3d, and O 1 s. The TEM images demonstrate the formation of hexagonal and half-hexagonal forms with varying orientations, as well as the emergence of elongated tetragonal shapes, upon increasing the temperature to 900 °C. the notable enhancement in light absorption, with the absorption bands spanning a wide range in the UV–vis spectra, specifically from approximately 300 nm to around 800 nm in the near-infrared (NIR) region. The broad range of PL emission bands identified by this mixture of nanoparticles, expanding from the UV to the near and intermediate IR regions, demonstrated that NO/TO nanocpomposites are considerably defective. The NO/TO nanocomposites exhibit efficient multi-color band emissions at ambient conditions, rendering them promising contenders for deployment in optoelectronic nanodevices, including blue, yellow, and white band emission light-emitting diodes and NIR luminescence bioimaging.

Folic Acid Passivated Efficient Cerium Doped Perovskite Nanocrystals for High‐Performance Light‐Emitting Diodes

AbstractThe 5d→4f transition of Ce3+ is allowed by the electric dipole and the parity selection rule and the position/intensity of the 5d excited state is strongly dependent on the materials’ composition and atomic structure. Herein, the composition‐dependent luminescence properties of Ce3+ in CsPbCl3‐xBrx (0 ≤ x ≤ 3) perovskite nanocrystals (PeNCs) are systematically revealed. It's observed that the 5d‐4f broadband emission of Ce3+ is greatly improved by optimizing the Cl:Br ratio due to the efficient energy transfer from excitons to Ce3+. Folic acid, a vitamin which is an extremely important cofactor, is introduced to regulate the film formation by interacting with uncoordinated ions. The modified CsPbCl1.5Br1.5 PeNCs with photoluminescence quantum yield of 91% represent a novel and extremely efficient white nanophosphor. Then, white light‐emitting diodes (WLEDs) are constructed by combining Ce3+‐doped PeNCs with 400‐nm ultraviolet chips with a luminous efficiency of 120.3 lm W−1, which is the most efficient perovskite single‐component WLED. Moreover, the blue‐violet LEDs are fabricated with external quantum efficiency of 0.84%, representing extremely high level of 400–435 nm perovskite LEDs. This work demonstrates the strategy in realizing high‐efficiency wavelength‐tunable PeNCs, motivating the further exploration of Ce3+‐doped perovskites in optoelectronic devices.

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

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 due to both 575 nm, which is related to the 4F9/2 → 6H13/2 and 482 nm that is ascribed to 4F9/2 → 6H15/2 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 optimised KCa(PO3)3 phosphors are 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. The lifetime values were used to calculate the quantum efficiency of the as prepared phosphors. 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.

The effects of LED lights in different colors on fattening performance, litter characteristics, meat properties, and some welfare parameters in broilers

Light is important for broiler rearing which can affect economically significant performance traits. The purpose of this study was to investigate the effects of daylight, warm white and blue LED light on broiler fattening performance, carcass characteristics, meat quality, litter characteristics and welfare. 216 male chicks were used. Chicks were weighed and housed randomly in 3 light-controlled rooms (n=72), each containing 9 separate pens (8 chicks per pen). During the experiment body weight, weight gain, feed consumption, and feed-to-gain ratio were calculated weekly. Carcass yield and percentages of internal organs were determined. Tonic immobility duration, footpad, and breast burns of broilers, pH, and moisture of litter, cooking loss, and water-holding capacity of the breast meat were analyzed. At the end of six weeks of the experiment, the body weight (P

Vacuum-Boosting Precise Synthetic Control of Highly Bright Solid-State Carbon Quantum Dots Enables Efficient Light Emitting Diodes.

Carbon quantum dots (C-dots) have emerged as efficient fluorescent materials for solid-state lighting devices. However, it is still a challenge to obtain highly bright solid-state C-dots because of the aggregation caused quenching. Compared to the encapsulation of as-prepared C-dots in matrices, one-step preparation of C-dots/matrix complex is a good method to obtain highly bright solid-state C-dots, which is still quite limited. Here, an efficient and controllable vacuum-boosting gradient heating approach is demonstrated for in situ synthesis of a stable and efficient C-dots/matrix complex. The addition of boric acid strongly bonded with urea, promoting the selectivity of the reaction between citric acid and urea. Benefiting from the high reaction selectivity and spatial-confinement growth of C-dots in porous matrices, in situ synthesize C-dots bonded can synthesized dominantly with a crosslinked octa-cyclic compound, biuret and cyanuric acid (triuret). The obtained C-dots/matrix complex exhibited bright green emission with a quantum yield as high as 90% and excellent thermal and photo stability. As a proof-of-concept, the as-prepared C-dots are used for the fabrication of white light-emitting diodes (LEDs) with a color rendering index of 84 and luminous efficiency of 88.14lm W-1, showing great potential for applications in LEDs.

In vitro culture of Campomanesia pubescens under different light qualities: a morphoanatomical and physiological characterization

Campomanesia pubescens (gabiroba) is a fruit tree that is native to the Cerrado and that has commercial potential and medicinal properties. It has recalcitrant seeds that do not tolerate desiccation and storage. Here, C. pubescens plants were grown in vitro under different light qualities. Light-emitting diodes (LEDs) were used at wavelengths for white (W) and blue in combination with red in the proportions BR (1:1), BR (1:3) and BR (3:1), at 100 ± 5 μmol m-2 s-1 over a 16-hour photoperiod. The leaf anatomy, chlorophyll a fluorescence, chloroplast pigments and malondialdehyde (MDA) content were evaluated. Studies on Cerrado plants grown in vitro focusing on light quality and its effects on plant development and growth are scarce. Records of anatomical and physiological C. pubescens characteristics when grown in vitro under different lighting qualities using LEDs are nonexistent. In this context, the aim of this study was to analyze the anatomical and physiological responses of C. pubescens seedlings from in vitro cultivation under different light qualities, to support future studies on the propagation and conservation of this species. This work is a pioneer for this species. When the plants were cultivated in combinations of blue/red LEDs 1:1 and 3:1, they yielded higher biomass, presenting higher epidermis and chlorenchyma values with greater stomatal density and functionality, better photosynthetic efficiency, higher Y(II) values, qP and higher total chlorophyll concentrations, and thus these lights did not cause oxidative damage compared to the white (control) LEDs. This study contributed to a better understanding of the anatomical and physiological changes in C. pubescens plants grown in vitro under different light qualities. C. pubescens plants exhibited varied anatomical and physiological characteristics depending on the spectrum of light used here. The combinations of BR (1:1) or BR (3:1) LEDs are promising for the propagation of the species, given their positive influence on most of the studied traits.

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.

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 the full width interconnection of subcells 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 are fabricated on both indium tin oxide (ITO) and ITO‐free substrates. Under 500 lux cool white light emitting diode 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.