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The Scaling of Ligand Concentration and Soret Effect Induced Phase Transition in CsPbBr3 Perovskite Quantum Dots
摘要： The intelligent chemistry strategy based automated machine is applied for the study of the phase transition in the CsPbBr3 quantum dots (QDs). With the in-situ photoluminescence (PL) signal detector and analysis module, the oleyl amine (OLA) and oleyl acid (OA) ligands concentration dependent diffusion picture are well derived, a three-stage power-law scaling is disclosed on the ligands concentration dependent growth, and a phase transformation from CsPbBr3 to Cs4PbBr6 QDs are confirmed. Based on the experimental analysis associated with the G0W0-BSE calculation, we confirmed that there is no significant PL signal in the pure Cs4PbBr6 structure. With the steady temperature control module, we find the ligand concentration and the Soret effect are isomorphic for the mass flux in the QDs nucleation and phase transformation. We find the activity of the surface states can be essential for the size dependence of the Soret effect in a general way.
关键词： CsPbBr3,Soret effect,quantum dots,phase transition,ligand concentration
更新于2025-09-16 10:30:52
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Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms
摘要： Phase-shifting electron holography (PS-EH) using a transmission electron microscope (TEM) was applied to visualize layers with different concentrations of carriers activated by Si (at dopant levels of 1019, 1018, 1017 and 1016 atoms cm?3) in n-type GaN semiconductors. To precisely measure the reconstructed phase pro?les in the GaN sample, three electron biprisms were used to obtain a series of high-contrast holograms without Fresnel fringes generated by a biprism ?lament, and a cryo-focused-ion-beam (cryo-FIB) was used to prepare a uniform TEM sample with less distortion in the wide ?eld of view. All layers in a 350-nm-thick TEM sample were distinguished with 1.8-nm spatial resolution and 0.02-rad phase-resolution, and variations of step width in the phase pro?le (corresponding to depletion width) at the interfaces between the layers were also measured. Thicknesses of the active and inactive layers at each dopant level were estimated from the observed phase pro?le and the simulation of theoretical band structure. Ratio of active-layer thickness to total thickness of the TEM sample signi?cantly decreased as dopant concentration decreased; thus, a thicker TEM sample is necessary to visualize lower carrier concentrations; for example, to distinguish layers with dopant concentrations of 1016 and 1015 atoms cm?3. It was estimated that sample thickness must be more than 700 nm to make it be possible to detect sub-layers by the combination of PS-EH and cryo-FIB.
关键词： phase-shifting electron holography,dopant pro?ling,carrier concentration,GaN,inactive layer,active layer
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Up-Conversion Threshold under Concentrated Sunlight
摘要： We investigate the two-photon threshold of rare-earth up-conversion under concentrated sunlight, in a solar furnace that generates an irradiance of up to 2606 suns on the samples. One of the most efficient up-converters currently available, NaYF4: Er3+ was used. We established a threshold by experimentally observing the transition for up-conversion photoluminescence from a quadratic relation to linear relation as solar concentration was increased. We further investigated the role of energy transfer on the threshold, observing the same threshold for a higher Er3+ content of 50%, but a threshold that exceeds 2300 suns at 15% Er3+. In this way, a tangible limit for the benefit and effect of solar concentration on up-conversion can be obtained for photovoltaic and solar thermal applications.
关键词： photovoltaic,concentrated sunlight,up-conversion,photoluminescence,solar concentration,solar thermal applications
更新于2025-09-16 10:30:52
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The Influence of Solar Spectrum and Concentration Factor on the Material Choice and the Efficiency of Multijunction Solar Cells
摘要： In this work, we revisit the theoretical study on the conversion efficiency of series-connected multijunction solar cells. The theoretical method, based on the detailed balance model, is then applied to devices with 2 to 6 junctions under different illumination conditions. As results, (i) we show that the peaks in the efficiency distribution occur for recurrent values of bottom junction bandgap energy corresponding to atmospheric absorption in the solar spectrum, and (ii) we demonstrate that variations in the number of junctions, in the incident solar spectrum, and in the concentration factor lead to changes in the optimum bandgap energy set but that the bottom junction bandgap energy only changes among the recurrent values presented before. Additionally, we highlight that high conversion efficiencies take place for a broad distribution of bandgap energy combination, which make the choice of materials for the device more flexible. Therefore, based on the overall results, we propose more than a hundred III-V, II-VI and IV semiconductor material candidates to compose the bottom junction of highly efficient devices.
关键词： conversion efficiency,material choice,concentration factor,Multijunction solar cells,solar spectrum
更新于2025-09-16 10:30:52
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Cytosolic delivery of quantum dots mediated by freezing and hydrophobic polyampholytes in RAW 264.7 cells
摘要： Quantum dots (QDs) can be delivered efficiently inside macrophages using a freeze-concentration approach. In this study, we introduced a new, facile, high concentration-based freezing technology of low toxicity. We also developed QD-conjugated new hydrophobic polyampholytes using poly-L-lysine (PLL), a naturally derived polymer, which showed sustained biocompatibility, stability over one week, and enhanced intracellular delivery. When freeze-concentration was applied, the QD-encapsulated hydrophobic polyampholytes showed a higher tendency to adsorb onto the cell membrane than the non-frozen molecules. Interestingly, we observed that the efficacy of adsorption of QDs on RAW 264.7 macrophages was higher than that on fibroblasts. Furthermore, the intracellular delivery of QDs using hydrophobic polyampholytes was higher than those of PLL and QDs. In vitro studies revealed the efficient endosomal escape of QDs in the presence of hydrophobic polyampholytes and freeze-concentration. Collectively, these observations indicated that the promising combination of freeze-concentration and hydrophobic polyampholytes may act as an effective and versatile strategy for the intracellular delivery of QDs, which can be used for biological diagnosis and therapeutic applications.
关键词： Macrophages,Quantum dots,Intracellular delivery,Hydrophobic polyampholytes,Freeze-concentration
更新于2025-09-16 10:30:52
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Luminescence declining behaviors in YAG:Ce transparent ceramics for high power laser lighting
摘要： High lumen-density laser lighting has become an advanced lighting technology. However, as an important component, transparent light-conversion materials exhibit low efficiency and luminescence declining behaviors, especially under high power density lasers, seriously restricting their potential applications. Herein, high quality YAG:Ce transparent ceramics (TCs) with different Ce concentrations and sizes were designed and fabricated for comparison with YAG:Ce single crystals to reveal the nature behind the above phenomena under the assistance of different encapsulated models of LED/LD devices. The highest luminous efficiency for the TCs of over 248 lm W?1 was achieved in the LED device, while only 170 lm W?1 could be reached for the LD devices. The strong thermal quenching and concentration quenching worked synergistically to result in the luminescence declining behavior in the 0.5 at% YAG:Ce ceramics, which have 80% and 20% responsibility after smart experimental comparison, respectively. Besides, the potential factors for the low efficiency in TC-based LD lighting were also revealed. Therefore, this work not only shows the optical performance of TCs in LED and LD applications, but also presents how the deep influence factors and excitation models lead to differences in their performance. It significantly reinforces the understanding of fundamental problems for TC-based high power laser lighting. These results are crucial for advancing TC-supported technologies in illumination, projection and scintillation.
关键词： transparent ceramics,concentration quenching,laser lighting,YAG:Ce,luminescence declining,thermal quenching
更新于2025-09-16 10:30:52
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Reverse Heterojunction (Al)GaInP Solar Cells for Improved Efficiency at Concentration
摘要： Mitigating series resistance is crucial to the efficiency of concentrator solar cells at high current density. Conventional AlGaInP junction designs for the top junction of III–V multijunction cells present a challenging tradeoff between series resistance on the one hand and current collection and voltage on the other hand. In this article we discuss the physics of a reverse heterojunction solar cell that aims to improve on this tradeoff by combining a high bandgap Al0.18Ga0.33In0.49P base and a lower bandgap (Al)GaInP emitter. The high mobility of the emitter leads to a relatively low series resistance, compared with a high bandgap homojunction cell. The electroluminescence spectrum shows emission peaks from both the emitter and base, leading to an open-circuit voltage that is not strictly dominated by either layer. The reverse heterojunction design is increasingly beneficial as the one-sun voltage increases.
关键词： heterojunction,III–V solar cell,Concentration,series resistance
更新于2025-09-16 10:30:52
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Analysis of spectroscopic information for detecting methane emissions on local paths using CO and He – Ne lasers
摘要： Measuring the concentration of methane in the atmosphere is demonstrated to be very important, since an increase in methane content enhances the greenhouse effect. It is shown that the error in assessing the concentration of CH4 depends on many factors, including the reliability of the parameters of the spectral absorption lines of gases, the accuracy of determining the concentration, the measurement error, etc. The spectroscopic information necessary to detect sources of high methane concentration in the atmosphere using CO and He – Ne lasers is analysed.
关键词： concentration,absorption spectrum,methane,differential absorption method,laser
更新于2025-09-16 10:30:52
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The 808?nm and 980?nm infrared laser irradiation affects spore germination and stored calcium homeostasis: A comparative study using delivery hand-pieces with standard (Gaussian) or flat-top profile
摘要： Photobiomodulation relies on the transfer of energy from incident photons to a cell photoacceptor. For many years the concept of photobiomodulation and its outcome has been based upon a belief that the sole receptor within the cell was the mitochondrion. Recently, it has become apparent that there are other photoacceptors operating in different regions of the electromagnetic spectrum. Alternative photoacceptors would appear to be water and mechanisms regulating calcium homeostasis, despite a direct effect of laser photonic energy on intracellular calcium concentration outwith mitochondrial activity or influence, have not been clearly demonstrated. Therefore, to increase the knowledge of intracellular?calcium and laser photon interaction, as well as to demonstrate differences in irradiation profiles with modern hand-pieces, we tested and compared the photobiomodulatory effect of 808 nm and 980 nm diode laser light by low- and higher-energy (60s, 100 mW/cm2, 100 mW/cm2, 500 mW/cm2, 1000 mW/cm2, 1500 mW/cm2, 2000 mW/cm2) irradiated with a “standard” (Gaussian fluence distribution) hand-piece or with a “flat-top” (uniform fluence) hand-piece. For this purpose, we used the eukaryote unicellular-model Dictyostelium discoideum. The 808 nm and 980 nm infrared laser light, at the energy tested directly affect the stored Ca2+ homeostasis, independent of the mitochondrial respiratory chain activities. From an organism perspective, the effect on Ca2+-dependent signal transduction as the regulator of spore germination in Dictyostelium, demonstrates how a cell can respond quickly to the correct laser photonic stimulus through a different cellular pathway than the known light-chromophore(mitochondria) interaction. Additionally, both hand-piece designs tested were able to photobiomodulate the D. discoideum cell; however, the hand-piece with a flat-top profile, through uniform fluence levels allows more effective and reproducible effects.
关键词： Mitochondria activities,Laser therapy,Photobiomodulation,Low-level laser therapy,Intracellular calcium concentration
更新于2025-09-16 10:30:52
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Design and Performance of a 1.5 axis Sun tracking Concentrated Photovoltaic System
摘要： This paper reports the design and testing of a concentrated solar photovoltaic thermal (CSPVT) system. The system consists of the PV panel, its cooling system, the parabolic concentrator, and the sun tracking mechanism. Photo Voltaic Thermal (PVT) systems are already a promising technique for improving energy yields and efficiencies of PV panels. The current work adds a concentration effect to make further improvements, especially on yields. Unlike the case of other research which uses plane mirrors along the sides of PV panels, this work employs a single parabolic reflector of concentration ratio 1.3, integrated with the panel mounting. A cooling system is also integrated with the mounting, so that the specially designed sun tracking mechanism turns the entire assembly, keeping both panel and reflector facing the sun without affecting the coolant flow in the adjoining pipes. This is one of the novelties of this work. We use vertical axis tracking but with seasonal adjustment of tilt. Hence the 1.5 axis in the title of this paper. Southern hemisphere spring tests in Cape Town showed a 60.2% electric power gain when compared with yields from an identical fixed panel. We also develop and test a MATLAB program using actual weather data for the experimentation period, and do a TRNSYS simulation using the software’s embedded TMY (typical meteorological year) weather data for the period. We find MATLAB results to be closer to experimental ones, while TRNSYS ones are not far out on totals. We conclude that CSPVT has much potential to increase both yields and efficiencies. In addition, we suggest that TRNSYS simulation would probably be most useful in cases where actual weather data is not available.
关键词： CSPVT,efficiency,concentration,solar tracking,photovoltaic thermal
更新于2025-09-16 10:30:52