Light-emitting Diodes Research Articles

Exploring Pyrazine-Based Organic Redox Couples for Enhanced Thermoelectric Performance in Wearable Energy Harvesters.

Thermoelectric generators (TEGs) based on thermogalvanic cells can convert low-temperature waste heat into electricity. Organic redox couples are well-suited for wearable devices due to their nontoxicity and the potential to enhance the ionic Seebeck coefficient through functional-group modifications. Pyrazine-based organic redox couples with different functional groups is comparatively analyzed through cyclic voltammetry under varying temperatures.The results reveal substantial differences in entropy changes with temperature and highlight 2,5-pyrazinedicarboxylic acid dihydrate (PDCA) as the optimal candidate.How the functional groups of the pyrazine compounds impact the ionic Seebeck coefficient is examined, by calculating the electrostatic potential based on density functional theory.To evaluate the thermoelectric properties, PDCA is integrated in different concentrations into a double-network hydrogel comprising poly(vinyl alcohol) and polyacrylamide. The resulting champion device exhibits an impressive ionic Seebeck coefficient (Si) of 2.99mV K-1, with ionic and thermal conductivities of ≈67.6 µS cm-1 and ≈0.49W m-1 K-1, respectively.Finally, a TEG is constructed by connecting 36 pieces of 20× 10-3 m PDCA-soaked hydrogel in series. It achieves a maximum power output of ≈0.28 µW under a temperature gradient of 28.3 °C and can power a small light-emitting diode. These findings highlight the significant potential of TEGs for wearable devices.

Ammonothermal Synthesis of Luminescent Imidonitridophosphate Ba4P4N8(NH)2:Eu2.

The structural variability of a compound class is an important criterion for the research into phosphor host lattices for phosphor-converted light-emitting diodes (pc-LEDs). Especially, nitridophosphates and the related class of imidonitridophosphates are promising candidates. Recently, the ammonothermal approach has opened a systematic access to this substance class with larger sample quantities. We present the successful ammonothermal synthesis of the imidonitridophosphate Ba4P4N8(NH)2:Eu2+. Its crystal structure is solved by X-ray diffraction and it crystallizes in space group Cc (no.9) with lattice parameters a=12.5250(3), b=12.5566(4), c=7.3882(2)Å and β=102.9793(10)°. For the first time, adamantane-type (imido)nitridophosphate anions [P4N8(NH)2]8- are observed next to metal ions other than alkali metals in a compound. The presence of imide groups in the structure and the identification of preferred positions for the hydrogen atoms are performed using a combination of quantum chemical calculations, Fourier-transform infrared, and solid-state NMR spectroscopy. Eu2+ doped samples exhibit cyan emission (λmax=498nm, fwhm=50nm/1981cm-1) when excited with ultraviolet light with an impressive internal quantum efficiency (IQE) of 41%, which represents the first benchmark for imidonitridophosphates and is promising for potential industrial application of this compound class.

Light emitting diodes for the improvement of postharvest quality of wild rocket in soilless and soil-bound cultivation systems

Wild rocket (Diplotaxis tenuifolia (L.) DC cv. Dallas) is a leafy green vegetable appreciated for its pungent taste and healthy properties, often consumed as a ready-to-eat product. The cultivation system is crucial in determining the overall quality, while postharvest storage is fundamental for preserving nutritional quality, phytochemicals, and vitamins. This study aimed to investigate the phytochemical content and microbiological quality of soilless (SS) and soil-bound (SB) wild rocket during cold postharvest storage under blue, red, and green Light Emitting Diode (LED). Blue LED increased chlorophylls and carotenoids in SB after two days of storage, and chlorophyll a in SS after seven days. Furthermore, it reduced H2O2 levels after two days (SS and SB) and lipid peroxidation in SB. Red LED increased phenols in both SS and SB but was detrimental to chlorophyll, carotenoids, and oxidative markers. Green LED had less significant effects. Microbiological growth varied with LED treatment: green light increased mesophilic bacteria in SB, and red light did so in SS by day four, while blue light reduced bacterial growth at the end of storage. Overall, Blue LED was the most effective LED in preserving postharvest quality. Soilless cultivation was particularly beneficial in reducing lipid peroxidation and maintaining cell membrane integrity during long-term storage, and it might also be more effective in preserving ascorbic acid. Conversely, soil-bound cultivation methods could enhance initial polyphenol content or better preserve it during early storage. This study highlights the complex interplay of pre-harvest conditions, postharvest quality, and shelf-life performance.

Effects of curing lights on polymerization shrinkage of composite attachments in clear aligner treatment: A microcomputed tomography study

This study aimed to investigate the polymerization shrinkage of composite attachments and changes in attachment templates during bonding in clear aligner treatments. A total of 24 extracted teeth were divided into 4 groups, and plaster models were digitized. Attachment templates were produced with beveled attachments on premolars and rectangular attachments on molars. Polymerizations used a halogen curing light (800 milliwatts per square centimeter [mW/cm2] for 20 seconds) and light-emitting diode (LED) curing light in 3 modes (1000 mW/cm2 for 20 seconds, 1000 mW/cm2 for 10 seconds, and 3200 mW/cm2 for 3 seconds). The curing distance was 5 mm, and temperature changes were recorded with a thermal camera. Microcomputed tomography scanning measured volumetric and linear attachments before and after polymerization. Statistical analyses employed a 1-way analysis of variance with Bonferroni corrected Tukey post-hoc for multiple comparisons and the Kruskal-Wallis test for temperature change. Significant differences (P<0.001) were found in temperature among curing lights. The highest temperature was in the LED unit-extra mode, and the lowest was in the halogen curing unit. The LED unit for 20 seconds caused the highest temperature change. A significant difference (P= 0.048) in occlusal attachment length was found between the LED unit for 20 seconds and the LED unit-extra mode. Polymerization resulted in increased attachment template thickness across all groups, with significant changes noted in the halogen unit, LED unit for 20 seconds, and LED unit-extra mode. Temperature generated during polymerization varied between halogen and LED curing lights. Significant differences were found in attachment length at the occlusal level and template thickness postpolymerization. Preferences in attachment bonding protocols may affect the clinical precision of clear aligner treatments.

Efficiency limits of concentrated solar thermophotonic converters under realistic conditions: The impact of nonradiative recombination and temperature dependence

A concentrated solar thermophotonic converter (CSTC) that efficiently harvests the entire solar spectrum under non-ideal conditions is proposed. This device includes an optical concentrator, a solar absorber, a GaAs light-emitting diode (LED) on the hot side, and an InP photovoltaic (PV) cell on the cold side. The electric power generated by the PV cell is utilized to positively bias the heated LED, resulting in a substantial increase in LED emission power. A comprehensive theoretical model is developed to accurately predict the output electrical performance and overall energy conversion efficiency of the CSTC device, especially considering the impact of the nonradiative recombination and temperature dependence. The calculated results show that when the solar concentrating factor is 30, and the LED and PV cell voltages are 0.989 V and 1.13 V, respectively, the overall peak efficiency can reach 12.8% and the corresponding output power density is 384 mW cm−2, achieving performance metrics nearly 4 orders of magnitude higher than solar thermophotovoltaics (TPV). Additionally, increasing the solar concentration ratio and decreasing the thickness of the semiconductor materials can further improve the overall output performance. This work reveals that CSTC offers several advantages over solar TPV, including more efficient conversion of narrow-spectrum electroluminescence, higher radiated power from the LED emitter, and the ability to operate at lower solar concentrations and lower costs.

Compound parabolic concentrator for LED-based underwater optical communication transmitter

Laser sources have been used at the transmitter unit of underwater wireless optical communication (UWOC) systems since their invention. In recent years, light-emitting diodes (LEDs) have begun to be used as UWOC transmitters due to their low cost, long lifespan, and high energy efficiency. However, data transmission distances in UWOC systems using bare LEDs and LED arrays with collimating lens are limited due to LED’s large divergence angles and insufficient gains provided by the low cost lens designs. In this paper, we propose to use a compound parabolic concentrator (CPC), whose transmission efficiency curve is very close to the ideal concentrator, as a collimator that narrows the divergence angle of LEDs to design low-cost UWOC transmitter with long communication distance. Using the Bouguer–Beer–Lambert channel model, we derived the received optical power expression at the receiver side for the LED-based UWOC system with CPC at the transmitter. Furthermore, unlike existing studies in the literature, the full spectrum of the LED has been taken into account when deriving the power expression. The results show that using the CPC collimator instead of a typical collimation lens in an LED-based UWOC system can narrow the divergence angle by approximately 10 times, resulting in a 70 dB increase in signal-to-noise ratio (SNR) at the receiver and up to a 20 times increase in the communication distance.

Mitigating bulk halide defects in blue-emissive perovskite nanocrystals using benzoyl halides for efficient light-emitting diodes

While recent advances have demonstrated highly efficient and stable perovskite light-emitting diodes (LEDs), blue perovskite LEDs still show low performance compared to green, red, near IR counterparts. Despite perovskites being well-known for their defect tolerance, blue perovskites are highly vulnerable to defects, which introduce deep trap states. In this study, we mitigated bulk halide vacancies in perovskite nanocrystals (PNCs) via the diffusion-assisted halide repairing strategy. We confirmed halide vacancies inside as-synthesized PNCs, both in the core and on the surface, through HADDF-STEM. By treating PNCs with benzoyl halides, these halide vacancies were further mitigated due to halide diffusion via concentration gradients between the surface and the core, resulting in enhanced PLQY of the PNCs. In the fabrication of blue PNC LEDs, this approach yielded a comparable efficiency with an EQE of 5.37 % at 469 nm, demonstrating the robustness of our method for efficient blue perovskite LEDs. Furthermore, the peak wavelengths of benzoyl halide-treated PNC LEDs remained stable during operation, whereas those of pristine PNC LEDs exhibited peak shifts. We believe that our novel approach can be universally applied to various types of perovskites, reducing bulk vacancies. This advancement will be a significant breakthrough for the performance enhancement of blue perovskite LEDs in the future.

Defect passivation with spectral shift for improved efficiency and stability of quasi-2D blue perovskite light emitting diodes

Metal halide perovskites are emerging as promising materials for next-generation light-emitting diodes (LEDs), owing to their cost-effectiveness, facile manufacturing, and excellent optoelectronic properties including a narrow emission-line full width at half maximum, high photoluminescence quantum yield, and spectral stability. However, blue-emission perovskite LEDs (PeLEDs) exhibit perovskite phase segregation and halogen ion migration during operation, attributed to crystal defects, halogen vacancies, and phase instability of mixed-halide perovskites. These defects compromise the spectral stability of blue-emitting PeLEDs, resulting in an undesirable color shift toward longer wavelengths. In this study, we introduce a dynamic treatment with phenylphosphonic dichloride (PPOCl2) to address these challenges and achieve blue-emitting PeLEDs. The chloride in PPOCl2 penetrates the quasi-2D sky-blue perovskite, reducing halide defects. Meanwhile, the phosphonic group forms covalent bonds with undercoordinated Pb on the perovskites, effectively passivating defects. PPOCl2-treated perovskite exhibits a spectral blue shift toward a deep-blue wavelength (≤467 nm), enhancing electroluminescence performance. The quasi-2D PPOCl2-treated PeLEDs achieve a maximum external quantum efficiency of 2.31 % with an emission peak at 488 nm. Dynamic treatment with PPOCl2 shows the potential to improve the performance and stability of blue emission perovskite-based LEDs, providing a spectral shift mechanism to achieve deep-blue emission in PeLEDs.

Thermistors and stacked thermopile on III-nitride LED wafer and their application for on-chip temperature measurement

Temperature measurement of devices in working state is of critical importance. In this work, GaN-based thermistors and a thermopile are monolithically integrated with a III-nitride blue light-emitting diode (LED) for the on-chip temperature measurement of the LED. The thermistor is based on the temperature-dependent resistance, and the stacked thermopile is based on the Seebeck effect. The measured results indicate that both thermistors and the thermopile can monitor the temperature of the LED sensitively. Due to the advantages of higher sensitivity and easier signal processing, the thermopile is more suitable for real-time monitoring.

Evaluation of riboflavin, nanocurcumin, and hydrogen peroxide under light conditions: reduction of mature dental biofilms and enamel mineral loss

BackgroundBiofilms are a potential harbor for many microorganisms. The aim of this study was to test the efficacy of riboflavin (Rib), nano-micelle curcumin (NC), and hydrogen peroxide (HP), alone and in combination with the respective light (light-emitting diode (LED) or 980 nm diode laser) on the reduction of Streptococcus mutans and Lactobacillus acidophilus dual-species biofilms and their effect on the enamel mineral loss. Materials and methodsThe biofilms were formed on saliva-coated enamel slabs. Then, the biofilms were treated with antimicrobial photodynamic therapy (PDT) based on LED, Rib, and NC photosensitizers and with HP also based on a 980 nm diode laser (n = 8 per group). A crystal violet assay was performed to determine the reduction of the dual-species biofilms. The enamel slabs were analyzed for calcium and phosphorus content by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). ResultsWhile HP-PDT showed a reduction of 37% (p < 0.001), PDT with NC resulted in an even greater reduction of dual-species biofilms (40%, p < 0.001) than HP- and Rib-mediated PDT. In the EDX test, no significant difference was found between the control group and the treatment groups. ConclusionsThe use of natural photosensitizers such as NC in PDT has an effect that may be potentially important in reducing caries-causing bacteria.

Imaging pollen using a Raspberry Pi and LED with deep learning

The production of low-cost, small footprint imaging sensor would be invaluable for airborne global monitoring of pollen, which could allow for mitigation of hay fever symptoms. We demonstrate the use of a white light LED (light emitting diode) to illuminate pollen grains and capture their scattering pattern using a Raspberry Pi camera. The scattering patterns are transformed into 20× microscope magnification equivalent images using deep learning. We show the ability to produce images of pollen from plant species previously unseen by the neural network in training. Such a technique could be applied to imaging airborne particulates that contribute to air pollution, and could be used in the field of environmental science, health science and agriculture.

Structure regulation and luminescence improvement of Gd3Ga5O12:Cr3+: An anti-thermal quenching NIR phosphor for multifunctional applications

Near-infrared (NIR) phosphors converted light emitting diodes (LEDs) are booming as next NIR light sources. But the quantum efficiency and thermal stability of the NIR phosphors need to be improved. Here, thermally stable garnet Gd3Ga5O12 is selected as the matrix and Cr3+ as the luminescent center to obtain Gd3Ga5O12:Cr3+ NIR phosphor. Equivalent smaller Lu3+ was adopted to regulate the structure of Gd3Ga5O12 to further improve the luminescence performance. By regulating the structure the emission spectra shift toward blue region and the intensity is improved. Optimized GdLu2Ga5O12:Cr3+ exhibits anti-thermal quenching behavior and the internal quantum efficiency reaches 73.69 %. Relative sensitivity value of the phosphor GdLu2Ga5O12:Cr3+ reaches 3.353 % K−1 at 423 K based on lifetime mode. LED device is fabricated by combining the phosphor GdLu2Ga5O12:Cr3+ and the commercial red phosphor with blue chip. Electroluminescence spectrum can cover the absorption spectra of the plant dyes well. The lettuce grow faster by adopting this LED device as compensating light source. This work provides an anti-thermal quenching NIR phosphor for multiple applications.

Ultrathin SiONC passivation of c-Si by UHV thermal annealing in O₂/N₂: Chemical composition, morphology, and photoluminescence insights

This study investigates the impact of Ultra-High Vacuum (UHV) Thermal annealing in a N₂/O₂ atmosphere on the passivation of Ar ion etched crystalline silicon (c-Si) surfaces. A comprehensive analysis of the resulting ultrathin Silicon OxyNitride Carbide layer (SiONC) was conducted using X-ray Photoelectron Spectroscopy (XPS), Ultra-Violet Spectroscopy (UPS), Photoluminescence Spectroscopy (PL), and Atomic Force Microscopy (AFM). XPS revealed a significant transformation in chemical composition from a carbon-rich contaminated surface SiO1.02C2.98 to an oxygen- and nitrogen-containing passivated layer SiO0.13N0.10C0.28. UPS measurements elucidated changes in the electronic structure and Fermi level position at the c-Si/SiONC interface. AFM imaging demonstrated the formation of non-uniform SiONC islands, influencing surface morphology. Notably, PL spectroscopy indicated enhanced orange and red luminescence with energies of 2.0 and 1.73 eV, respectively, attributed to the SiONC layer. The enhanced luminescence, coupled with improved thermal stability and oxidation resistance, positions the SiONC layer as a promising material for advancing the performance of silicon-based optoelectronic devices, such as solar cells and light-emitting diodes (LEDs). This study provides fundamental insights into the correlation between the chemical, electronic, and morphological properties of the SiONC layer and its potential for improving c-Si device performance.

Flexible electronic-photonic 3D integration from ultrathin polymer chiplets

Integrating flexible electronics and photonics can create revolutionary technologies, but combining these components on a single polymer device has been difficult, particularly for high-volume manufacturing. Here, we present a robust chiplet-level heterogeneous integration of polymer-based circuits (CHIP), where ultrathin polymer electronic and optoelectronic chiplets are vertically bonded at room temperature and shaped into application-specific forms with monolithic Input/Output (I/O). This process was used to develop a flexible 3D integrated optrode with high-density microelectrodes for electrical recording, micro light-emitting diodes (μLEDs) for optogenetic stimulation, temperature sensors for bio-safe operations, and shielding designs to prevent optoelectronic artifacts. CHIP enables simple, high-yield, and scalable 3D integration, double-sided area utilization, and miniaturization of connection I/O. Systematic characterization demonstrated the scheme’s success and also identified frequency-dependent origins of optoelectronic artifacts. We envision CHIP being applied to numerous polymer-based devices for a wide range of applications.

Stiffness and Interface Engineered Soft Electronics with Large-Scale Robust Deformability.

Skin-like stretchable electronics emerge as promising human-machine interfaces but are challenged by the paradox between superior electronic property and reliable mechanical deformability. Here, a general strategy is reported for establishing robust large-scale deformable electronics by effectively isolating strains and strengthening interfaces. A copolymer substrate is designed to consist of mosaic stiff and elastic areas with nearly four orders of magnitudes modulus contrast and cross-linked interfaces. Electronic functional devices and stretchable liquid metal (LM) interconnects are conformally attached at the stiff and elastic areas, respectively, through hydrogen bonds. As a result, functional devices are completely isolated from strains, and resistances of LM conductors change by less than one time when the substrate is deformed by up to 550%. By this strategy, solar cells, wireless charging antenna, supercapacitors, and light-emitting diodes are integrated into a self-powered electronic skin that can laminate on the human body and exhibit stable performances during repeated multimode deformations, demonstrating an efficient path for realizing highly deformable energy autonomous soft electronics.

Inducing Multicolour emission in MEH-PPV/TiO2 nanocomposites

Fluorescence-based polymers have a wide variety of applications such as light-emitting diodes, optoelectronics, and biosensors. The present study endeavors towards the effect of TiO2 nanoparticles (calcined at various temperature) on the emission of Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) and to induce multicolor emission. The TiO2 nanoparticles synthesized by sol-gel method were calcined at 400°C and 600°C. In situ polymerization was adopted to synthesize MEH-PPV / TiO2 nanocomposites and the structural characteristics of the nanocomposites were studied using Fourier transformed Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The photo-physical characteristics of the nanocomposites were investigated using UV-Visible spectroscopy, Photoluminescence spectroscopy, and Fluorescence microscopy. TiO2 nanoparticles calcined at 400°C demonstrates anatase phase, whereas the particles calcined at 700°C exhibits mixed phase of rutile and anatase. The study reveal that calcination temperature has a strong impact on the morphology of the synthesized nanoparticles. The photoluminescence spectra reveal that the incorporation of TiO2 nanoparticles enhances the red orange emission intensity of MEH-PPV, additionally exhibits emission at multiple wavelengths. Fluorescence microscopy evidences multiple colour emission from MEH-PPV/TiO2 nanocomposites. The multiple emission in the polymer nanocomposite is arised from the oxygen vacancies present in anatase and rutile phases of TiO2 nanoparticle.

Only incandescent light significantly decreases feeding of Anopheles funestus s.s. (Diptera: Culicidae) mosquitoes under laboratory conditions

Recent work has demonstrated that exposure to artificial light at night (ALAN) may alter mosquito feeding behavior and so must be considered a moderator of vector-borne disease transfer. Anopheles funestus mosquitoes are a primary malaria vector in sub-Saharan Africa, but no study to date has tested the impact of ALAN on their feeding behavior. Here we test if the exposure to commonly used household lights (compact fluorescent lights, light-emitting diodes, and incandescent lights) alters Anopheles funestus feeding. Mated, unfed female mosquitoes were exposed to a light treatment, at the onset of darkness, followed by a blood-feeding assay. The light treatments consisted of a 30-min light pulse of one of the three household lights, each in individual experimental containers, versus controls. All three household lights resulted in a reduction in the percentage of females taking a blood meal, but only mosquitoes exposed to incandescent light showed a statistically significant reduction in feeding of 19.6% relative to controls which showed a 42.8% feeding rate. Our results suggest that exposure to some household lights during the night may have an immediate inhibitory effect on Anopheles funestus feeding. By helping identify which light types lead to a suppression of feeding, the findings of this study could provide insight necessary to design household lights that can help minimize mosquito feeding on humans.

High-yield Micro-LED laser transfer accomplished using an ablation-type release material

Micro light-emitting diode (Micro-LED) is a highly promising technology in the field of new displays, with the mass transfer process involved in its manufacturing process widely regarded as a major barrier to their further development. This study adopts laser transfer technology as the primary solution, using ablation-type transfer release materials that improve chip utilization rates over blister-type release materials. In addition, measurement of the laser transfer parameters, inspection, and laser repair technology are combined to achieve a transfer yield of about 100% to the carrier substrate and a cumulative transfer displacement of less than 1 µm in the Micro-LED inverted chip array. Furthermore, cleaning agents were used to remove adhesive residue from the receiving substrate after transfer, improving the bonding yield between the chip and the thin film transistor driver circuit board. This study provides a feasible solution for Micro-LED mass transfer, which could boost its further development toward commercial application.

Insights into the pressure-dependent physical properties of cubic Ca3MF3 (M = As and Sb): First-principles calculations

Here, first-principles calculations have been employed to make a comparative study on structural, mechanical, electronic, and optical properties of new Ca3MF3 (M = As and Sb) photovoltaic compounds under pressure. The findings disclose that these two systems possess a direct band gap, showcasing a large tunable range under pressure, effectively encompassing the visible light spectrum. Adjusting various levels of hydrostatic pressure has effectively tuned both the band alignment and the effective masses of electrons and holes. Both compounds were initially identified as brittle materials at 0 GPa pressure; however, as the pressure increases, they transform, becoming highly anisotropic and ductile. Due to the material's mechanical robustness and enhanced ductility, as evidenced by its stress-induced mechanical properties, the Ca3MF3 (M = As and Sb) material shows potential for use in solar energy applications. Furthermore, as the influence of external pressure increases, the absorption edge seems to move slightly towards lower energy region. Optical properties show that the materials studied might be used from several optoelectronic devices in the visible and ultraviolet range area. Our findings show that pressure considerably influences the physicochemical properties of Ca3MF3 (M = As and Sb) compounds, which is a promising feature that can be useful for optoelectronic and photonic applications, for instance, light-emitting diodes, photodetectors, and solar cells.

Dual-Functional Cs3Bi2Br9 for stable all-solid-state photo-rechargeable batteries

In light of the immense potential solid-state photo-rechargeable batteries hold in the efficient utilization of renewable solar energy, there is a rapidly growing demand for materials that possess both energy harvesting and storage capabilities. In this study, a solid-state photo-rechargeable battery has been designed based on the FTO(Fluorine-doped SnO2 transparent conductive glass)/TiO2/Cs3Bi2Br9/Pt/FTO system, which achieves dual functions of photoelectric conversion and energy storage. The inorganic bismuth-based material employed in these batteries exhibits commendable cyclic stability. Under photo-rechargeable conditions, a single cell can maintain an open-circuit voltage as high as 0.45 V in the absence of illumination. By connecting multiple cells in series, we succeed in powering an LED (Light-emitting diode) continuously for 1 min without light exposure. The findings of this research open new avenues for the design and development of novel materials that could enable highly efficient solid-state photo-rechargeable batteries.