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Luminescence Line Broadening of CdSe Nanoplatelets and Quantum Dots for Application in w-LEDs
摘要： Nanoplatelets (NPLs) of CdSe are an emerging class of luminescent materials, combining tunable and narrow emission bands with high quantum yields. This is promising for application in white light LEDs (w-LEDs) and displays. The origin of the narrow spectral width of exciton emission in core NPL compared to core-shell NPL and quantum dot (QD) emission is not fully understood. Here we investigate and compare temperature dependent emission spectra of core and core-shell CdSe NPLs and QDs. A wide temperature range, 4 to 423 K, is chosen to gain insight in contributions from homogeneous and inhomogeneous broadening and also to extend measurements into a temperature regime that is relevant for operating conditions in w-LEDs (T~423 K). The results show that temperature induced homogeneous broadening does not strongly vary between the various CdSe nanostructures (ΔEhom≈60-80 meV at 423 K) indicating that electron-phonon coupling strengths are similar. Only for the smallest QDs stronger coupling is observed. The origin of the narrow bandwidth reported at 300 K for core CdSe NPLs is attributed to a very narrow inhomogeneous linewidth. At 423 K the spectral width of NPL exciton emission is still superior to that of QDs. A comparison with traditional w-LED phosphors is made to outline advantages (tunability, narrow bandwidth, high efficiency) and disadvantages (color shift, stability issues) of NPLs for application in w-LEDs.
关键词： w-LEDs,Quantum Dots,Temperature dependent emission spectra,CdSe Nanoplatelets,Luminescence
更新于2025-09-23 15:21:01
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Degradation of InGaN-based LEDs: Demonstration of a recombination-dependent defect-generation process
摘要： This paper provides insights into the degradation of InGaN-based LEDs by presenting a comprehensive analysis carried out on devices having two quantum wells (QWs) with different emission wavelengths (495 nm and 405 nm). Two different configurations are considered: one with the 495 nm QW closer to the p-side and one with the 495 nm QW closer to the n-side. The original results collected within this work indicate that (i) during stress, the devices show an increase in defect-related leakage both in reverse and low-forward voltage ranges: current increases with the square-root of stress time, indicating the presence of a diffusion process; (ii) stress induces a decrease in the luminescence signal emitted by both quantum wells: the drop in luminescence is stronger when measurements are carried out at low current levels, indicating that degradation is due to the generation of Shockley–Read–Hall recombination centers; (iii) remarkably, the degradation rate is linearly dependent on the luminescence signal emitted before stress by the well, indicating that carrier density impacts on degradation; and (iv) the optical degradation rate has a linear dependence on the stress current density. The results strongly suggest the existence of a recombination-driven degradation process: the possible role of Shockley–Read–Hall and Auger recombination is discussed. The properties of the defects involved in the degradation process are described through steady-state photocapacitance measurements.
关键词： quantum wells,Shockley–Read–Hall recombination,Auger recombination,degradation,steady-state photocapacitance,InGaN-based LEDs
更新于2025-09-23 15:21:01
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GreenLight a?? An open source model for greenhouses with supplemental lighting: Evaluation of heat requirements under LED and HPS lamps
摘要： Greenhouse models are important tools for the analysis and design of greenhouse systems and for offering decision support to growers. While many models are available, relatively few include the influence of supplementary lighting on the greenhouse climate and crop. This study presents GreenLight, a model for greenhouses with supplemental lighting. GreenLight extends state of the art models by describing the qualitative difference between the common lighting system of high-pressure sodium (HPS) lamps, and the newest technology for horticultural lighting - the light-emitting diodes (LEDs). LEDs differ from HPS lamps in that they operate at lower temperatures, emit mostly convective heat and relatively little radiative heat, and can be more efficient in converting electricity to photosynthetically active radiation (PAR). These differences can have major implications on the greenhouse climate and operation, and on the amount of heat that must be supplied from the greenhouse heating system. Model predictions have been evaluated against data collected in greenhouse compartments equipped with HPS and LED lamps. The model predicted the greenhouse's heating needs with an error of 8e51 W m-2, representing 1e12% of the measured values; the RMSE for indoor temperature was 1.74e2.04 °C; and the RMSE for relative humidity was 5.52e8.5%. The model is freely available as open source MATLAB software at https://github.com/davkat1/GreenLight. It is hoped that it may be further evaluated and used by researchers worldwide to analyse the influence of the most recent lighting technologies on greenhouse climate control.
关键词： Energy use,Greenhouse lighting,LEDs,Greenhouse models,Crop models,Open source
更新于2025-09-23 15:21:01
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Design and Simulation of Low Circadian Action Micro-LED Displays with Four Primary Colors
摘要： Nowadays, displays are ubiquitous in our daily lives. Long-time exposure to a display’s unnatural light could influence the user’s circadian rhythm, especially at night. Here, we propose a four-color micro-light-emitting diode (LED) display to achieve low circadian action for nighttime uses. Specifically, we evaluate the RGBW-type (red, green, blue, and white) and RYGB-type (red, yellow, green, and blue) micro-LED displays in terms of circadian effect and color gamut coverage. With the addition of an extra white subpixel, it was found that the circadian effect at night can be reduced dramatically, but the color gamut remains unchanged. However, with an additional yellow subpixel, both the circadian effect and color gamut were found to improve. Finally, we simulated the circadian illuminance of real image contents for different displays. In comparison with existing liquid crystal displays, organic LED displays, and RGB (red, green, blue) micro-LED displays, the proposed four-primary-color micro-LED displays can significantly reduce the circadian effect at night.
关键词： micro-LEDs,circadian action,four primary colors
更新于2025-09-23 15:21:01
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Synthesis and optical studies of nanocrystalline Eu2+-doped and RE3+(Nd3+, Dy3+)-codoped Ba4Al14O25 materials for UV-LEDs
摘要： Green emitting Ba4Al14O25:Eu2+ and Ba4Al14O25:Eu2+,RE3+ (RE3+ = Nd3+, Dy3+) phosphors for ultraviolet light emitting diodes (UV-LEDs) were prepared via combustion technique at 600 °C. The as-prepared samples were reheated at 1150 (2 h) and 1350 °C (6 h) in a tube furnace under reducing condition (95 % dinitrogen and 5 % dihydrogen). The photoluminescence emission (PL) spectra were recorded to examine the effect of temperature and presence of co-dopants on the luminescence properties of materials. On excitation at 362 nm, PL spectra of these phosphors exhibited intense band at 480?520 nm due to spin-allowed 4f65d1→4f7 transition in Eu2+. The luminescence intensity and persistence behaviour of materials was improved in presence of Nd3+ and Dy3+ ions as codopants. The diffraction analysis confirmed the synthesis of lattice having orthorhombic structure with Pmma symmetry. The crystalline nature of samples was found to be increased at higher temperature. Transmission electron microscope (TEM) images exhibited that the prepared materials have nearly spherical shape in nano-range. The structure and chemical bonding of materials were supported by Fourier transform infrared (FTIR) spectra.
关键词： Nanocrystalline,Ba4Al14O25,Luminescence,TEM,UV-LEDs,Persistence
更新于2025-09-23 15:21:01
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A novel double-perovskite LiLaMgTeO6: Mn4+ far-red phosphor for indoor plant cultivation white LEDs: Crystal and electronic structure, and photoluminescence properties
摘要： Deep-red-emitting Mn4t activated oxide phosphors are the hot research topic due to their potential applications in indoor plant cultivation LEDs. In this paper, a novel double-perovskite LiLaMgTeO6:Mn4t phosphor was firstly prepared by high-temperature solid-state reaction method and its structure of the phosphor was determined by X-ray diffraction (XRD) and Rietveld refinement. Density functional theory (DFT) calculations using VASP provide an insight into the bandgap and electronic structures of the LiLaMgTeO6 host. Under UV or blue excitation, LiLaMgTeO6:Mn4t shows a good stability and bright far-red light in the 540e800 nm range with the maximum at 708 nm, which matches well with the absorption band of phytochrome PFR, indicating its potential application in improving plant growth. The optimal Mn4t doping concentration was approximately 0.6 mol%. Furthermore, a white-LEDs device made of a 365 nm chip coated with present phosphor and commercial green, blue phosphors was designed for indoor plant cultivation. The results indicate that the LiLaMgTeO6: Mn4t phosphor possesses great application prospect in white-LEDs for plant cultivation.
关键词： Far red emission,Phytochrome,Double perovskite,LEDs,Thermal stability,Indoor plant cultivation
更新于2025-09-23 15:21:01
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Synthesis and photoluminescence properties of Ln3+ (Ln3+= Sm3+/Eu3+) doped Na2NbAlO5 phosphors
摘要： A series of Ln3+ (Ln3+=Sm3+/Eu3+) ions doped Na2NbAlO5 phosphors have been synthesized by solid-state method. Sm3+ and Eu3+ ion doped phosphors are characterized by SEM, XRD, EDX, photoluminescence, decay and thermal stability profiles. The Ln3+-doped samples are consistent with the pure Na2NbAlO5 phase which were analyzed by the X-ray diffraction result. SEM results showed the homogeneous aggregates and particles size of Sm3+ (0.6-0.9μm) and Eu3+ (0.2-0.3μm) doped Na2NbAlO5. From EDX diagram, the samples are consisted of Na, Nb, Al, O and Sm ,or Eu elements.With the introduction of Eu3+ ions, the decay curves of Sm3+ decreases monotonically, which supports the occurrence of the energy transfer from Sm3+ to Eu3+ in Na2NbAlO5 host. The fluorescence lifetime decreases with increasing temperature . The energy transfer mechanisms of Sm3+ and Eu3+ doped Na2NbAlO5 have been investigated and can be derived to be electric dipole-dipole and diopole-quadrupole interactions, respectively. In addition, the temperature-dependent emission spectra of Sm3+/Eu3+ doped Na2NbAlO5 phosphors possess superior thermal stability. Under the ultraviolet light, the prepared Na2-xNbAlO5: xLn3+ (Ln3+= Sm3+/Eu3+) phosphors show the characteristic orange (Sm3+), red (Eu3+) emissions respectively. The obtained results suggest that the new Na2NbAlO5:xLn3+ (Ln3+= Sm3+/Eu3+) phosphors are promising candidates for white light-emitting diodes.
关键词： Photoluminescence,White LEDs,Energy transfer,Na2NbAlO5
更新于2025-09-23 15:21:01
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[IEEE 2019 19th International Conference on Control, Automation and Systems (ICCAS) - Jeju, Korea (South) (2019.10.15-2019.10.18)] 2019 19th International Conference on Control, Automation and Systems (ICCAS) - Relationship between LED Energy Consumption and Plant Growth in Small Hydroponic Plant Cultivation System
摘要： Global population growth and the ongoing climate crisis pose immense risk to the stable food supplies in the future. We have developed a small hydroponic plant cultivation system to ensure even in extreme circumstances. To build a sustainable system, we have utilized an LED lighting system together with conserved energy generated by sunlight. Such hydroponic plant cultivation systems have to operate at an affordable yet efficient principle. In this paper, we examine experimental results of the relationship between LED energy consumption and plant growth in a hydroponic plant cultivation system. LED light intensity directly correlates to electrical power consumed. Energy consumption is the result of electrical power consumed over a period of time. Three experiments with varying conditions utilizing constant electrical energy consumption were conducted. Case-1: Electric power is kept low and the lighting duration is long; Case-2: the electric power is set to medium and the lighting duration is medium; Case-3: the electric power is large and the lighting duration is short. As a result of evaluating the weight of grown lettuces, it was found that lettuce growth is excellent in Case-1. It means that the longer the LED irradiation duration, the better the plant growth even under the same energy consumption conditions.
关键词： Lighting duration,LEDs,Leaf lettuce growth,Energy consumption,Indoor hydroponic system
更新于2025-09-23 15:19:57
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Highly solid-luminescent graphitic C <sub/>3</sub> N <sub/>4</sub> nanotubes for white light-emitting diodes
摘要： Graphitic C3N4 (g-C3N4) has seldom been used for white light-emitting diode (LED) phosphors due to its low solid-state fluorescence quantum yield. Here, we report a facile thermal condensation path for the synthesis of g-C3N4 nanotubes stuffed with quantum dots. The g-C3N4 nanotubes have a high fluorescence quantum yield of 30.92% in the solid state. Nitrogen-rich and graphitic carbon-free features are responsible for the enhanced quantum efficiency. The photoluminescence quantum yield can be controlled and improved by the reaction temperature. We finally demonstrate white light emission by coating the highly solid-luminescent g-C3N4 nanotubes as phosphors onto a 370 nm ultraviolet LED.
关键词： graphitic carbon nitride,nanotubes,fluorescence,phosphors,white LEDs
更新于2025-09-23 15:19:57
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Heavy Atom Effect of Selenium for Metal-Free Phosphorescent Light-Emitting Diodes
摘要： Room-temperature phosphorescence from metal-free purely organic molecules has recently gained much interest. We devised metal-free organic phosphors by incorporating selenium (Se) to promote spin?orbit coupling by its nonmetal heavy atom effect. The Se-based organic phosphors showed bright phosphorescent emission in organic light-emitting diodes (OLEDs) and photo-excited phosphorescence in an amorphous film state. Large orbital angular momentum change (ΔL) during the electron transition process and heavy atom effect of Se render a PL quantum yield of 0.33 ± 0.01 and a high external quantum efficiency (EQE) of 10.7 ± 0.14% in phosphorescent LEDs. This work demonstrates the rational molecular design of metal-free organic phosphorescent emitters with Se as an alternative novel class of materials to the conventional organometallic phosphors for OLEDs.
关键词： organic light-emitting diodes,spin?orbit coupling,selenium,metal-free organic phosphors,phosphorescent LEDs,room-temperature phosphorescence
更新于2025-09-23 15:19:57