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Bright Cool White Emission from Ultrasmall CdSe Quantum Dots
摘要： In this work we employ a post-synthesis ligand treatment of ultrasmall CdSe quantum dots (QDs) with citric acid to increase the quantum yield (QY) of the of the as-synthesized CdSe from an average of 5.7% to a maximum of 61.3%. This is the highest reported value for a single component white-light emitting QD. The white-light emission of the ultrasmall CdSe quantum dots is derived from three surface states: pinned emission at a trap state associated with the phosphonic acid surface ligand, a surface Se state, and conventional deep trap states. The citric acid treated CdSe QDs were found to recover band gap emission from the phosphonic acid ligand trap state emission, exhibiting behavior . This band gap emission peak also becomes more prominent, resulting in a cooler white, as indicated by the shift in the CIE coordinates from an average of (0.30, 0.36) to (0.26, 0.32). Comparing to a previous method of increasing the QY by a post-synthesis treatment of formic acid, the citric acid treated CdSe QDs are brighter as well as more stable in solution over time, which opens the possibility for use in multiple applications.
关键词： white-light emission,quantum yield,quantum dots,citric acid,CdSe
更新于2025-09-12 10:27:22
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Efficient Quasi-Two-Dimensional Perovskite Light-Emitting Diodes with Improved Multiple Quantum Well Structure
摘要： Quasi-two-dimensional (quasi-2D) perovskites with a multiple quantum well structure can enhance the exciton binding energy and controllable quantum con?ne e?ect, which are attractive materials for e?cient perovskite light-emitting diodes (PeLEDs). However, the multiphase mixtures contained in these materials would cause nonradiative recombination at the perovskite ?lm surface. Here, a facile solution surface treatment is adopted to improve the multiple quantum well structure of the quasi-2D perovskite emitting layer, which can reduce the in?uence of defectinduced nonradiative recombination and the electric-?eld-induced dissociation of excitons for the PeLEDs. The improved multiple quantum well structure is veri?ed by UV absorption spectra and temperature-dependent photoluminescence spectra measurements. The photoluminescence quantum yield of the quasi-2D perovskite ?lm with surface treatment has been approximately increased by 200%. Meanwhile, the electroluminescence device achieves a current e?ciency of 45.9 cd/A.
关键词： electroluminescence,quasi-two-dimensional perovskite light-emitting diodes,surface treatment,multiple quantum well structure,photoluminescence quantum yield
更新于2025-09-12 10:27:22
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Manipulation of 3D nanocarbon hybrids toward synthesis of N-doped graphene quantum dots with high photoluminescence quantum yield
摘要： Synthesis of heteroatom-doped graphene quantum dots (GQDs) via a top-down approach is still challenging. Herein, we conveniently synthesized nitrogen-doped GQDs (N-GQDs) via an electrochemical method. In that, the N-containing 3D nanocarbon hybrids were prepared as the carbon and nitrogen sources, which were cut into small fragments in ammonia solution as the electrolyte. Interestingly, N-atoms from the 3D nanocarbon hybrids were successfully retained or converted into the other type of N in the obtained GQDs, resulting to a highly doped N content up to 12.3% even after excluding the amino- and pyrrolic N at edges of the N-GQDs. As a matter of fact, such synthesized N-GQDs show highly crystallized structure, and demonstrate a high photoluminescence quantum yield of ~19.3%, among the highest values of top-down approach synthesized GQDs. Moreover, it can be also used for adjusting the absorption range of GQDs. Overall, we developed a new strategy to synthesize N-doped GQDs by controlling the carbon source, which opens a new avenue toward achieving other types of heteroatom-doped GQDs.
关键词： electrochemical method,3D nanocarbon hybrids,doping,quantum yield,graphene quantum dots
更新于2025-09-11 14:15:04
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Effects of Zn <sup>2+</sup> and Ga <sup>3+</sup> doping on the quantum yield of cluster-derived InP quantum dots
摘要： As the commercial display market grows, the demand for low-toxicity, highly emissive, and size-tunable semiconducting nanoparticles has increased. Indium phosphide quantum dots represent a promising solution to these challenges; unfortunately, they typically suffer from low inherent emissivity resulting from charge carrier trapping. Strategies to improve the emissive characteristics of indium phosphide often involve zinc incorporation into or onto the core itself and the fabrication of core/shell heterostructures. InP clusters are high fidelity platforms for studying processes such as cation exchange and surface doping with exogenous ions since these clusters are used as single-source precursors for quantum dot synthesis. Here, we examined the incorporation of zinc and gallium ions in InP clusters and the use of the resultant doped clusters as single-source precursors to emissive heterostructured nanoparticles. Zinc ions were observed to readily react with InP clusters, resulting in partial cation exchange, whereas gallium resisted cluster incorporation. Zinc-doped clusters effectively converted to emissive nanoparticles, with quantum yields strongly correlated with zinc content. On the other hand, gallium-doped clusters failed to demonstrate improvements in quantum dot emission. These results indicate stark differences in the mechanisms associated with aliovalent and isovalent doping and provide insight into the use of doped clusters to make emissive quantum dots.
关键词： Indium phosphide,core/shell heterostructures,quantum yield,gallium doping,quantum dots,zinc doping
更新于2025-09-11 14:15:04
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A Facile One Step Hydrothermal Synthesis of Carbon Quantum Dots For Label -Free Fluorescence Sensing Approach to Detect Picric Acid in Aqueous Solution
摘要： In this work, a facile one step approach has been applied for the synthesis of nitrogen and sulphur co-doped water soluble carbon quantum dots (NS-CQDs) through hydrothermal treatment of L-Lysine and thiourea. The obtained NS-CQDs have a high quantum yield (QY) of 53.19 % and emit strong blue fluorescence under UV light excitation of wavelength 365 nm. The morphology of NS-CQDs is spherical in shape and their sizes are distributed in the range 5-8 nm with average diameter 6.86 nm. Moreover the NS-CQDs show excitation dependent emission behavior due to quantum confinement effect. Additionally, NS-CQDs serve as a fluorescent probe for the selective and sensitive detection of picric acid (PA) in aqueous solution. A good linear response to PA in the concentration range 1-10 μM with a detection limit 0.24 μM has been obtained. The high selectivity of PA by NS-CQDs is suggested to be arises from fluorescence resonance energy transfer (FRET) mechanism. Finally these NS-CQDs fluorescent probes have been examined in real water sample by measuring the concentration of PA in tap water.
关键词： Fluorescence,quantum yield,Picric acid,Carbon quantum dots
更新于2025-09-11 14:15:04
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Ultrafast Dynamics and Ultrasensitive Single-Particle Intermittency in Small-Sized Toxic Metal Free InP Based Core/Alloy-shell/Shell Quantum Dots: Excitation Wavelength Dependency Towards Variation of PLQY
摘要： Observation of strong deviation of photoluminescence excitation curve from absorption curve specially at lower wavelength range, below 450 nm in case of small sized toxic metal free InP based core-alloy-shell quantum dots hints towards interesting exciton dynamics. PL quantum yield (PLQY) has been observed to be dependent on the excitation wavelength. Monitoring the bleach dynamics employing femtosecond ultrafast pump-probe technique it could be shown that the rise-time increases with decrease in pump excitation wavelength from 100 fs for 550 nm excitation to 220 fs for 430 nm pump/excitation. Therefore exciton cooling takes longer time for lower wavelength excitation and thus the exciton becomes more prone to get trapped. About two fold enhancement in magnitude of normalized bleach signal at the band edge (~0.1 (for 430nm excitation) to ~0.2 (for 550nm excitation)) following exciton relaxation has been observed. Thus, in comparison to lower wavelength excitation, for near band-edge pump/excitation there is higher probability of radiative exciton recombination, therefore increasing PLQY. Hot exciton trapping dynamics has been noted to be occurring at a timescale ~750 fs. From ultra-sensitive single particle measurement, magnitude of power-law exponent for both ON and OFF events remain similar to each other and the magnitude remains unaltered for different excitation wavelengths, (405 nm to 568 nm). As long as 100 s ON event could be observed making this InP based non-toxic QD quite suitable for single particle tracking etc. Interestingly, ON event truncation time has been found to increase from 6s to 16s and OFF event truncation time has been found to decrease from 11s to 5.5s, thereby exciton detrapping rate / trapping rate increases from 0.5 to nearly 3 on going from 405 nm to 568 nm excitation. Thus, as the trapping gets suppressed and detrapping gets enhanced, PLQY gets enhanced. The extent of relative decrease of PLQY value with increase in excitation energy above band-edge has been observed to be much more pronounced in CdSe based CAS QD than InP based CAS QD.
关键词： ultrafast dynamics,photoluminescence quantum yield,excitation wavelength dependency,InP based quantum dots,single-particle intermittency
更新于2025-09-11 14:15:04
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Facile preparation of high fluorescent carbon quantum dots from orange waste peels for nonlinear optical applications
摘要： A facile and eco‐friendly hydrothermal method was used to prepare carbon quantum dots (CQDs) using orange waste peels. The synthesized CQDs were well dispersed and the average diameter was 2.9 ± 0.5 nm. Functional group identification of the CQDs was confirmed by Fourier transform infrared spectrum analysis. Fluorescence properties of the synthesized CQDs exhibited blue emission. The fluorescence quantum yield of the CQDs was around 11.37% at an excitation wavelength of 330 nm. The higher order nonlinear optical properties were examined using a Z‐scan technique and a continuous wave laser that was operated at a wavelength of 532 nm. Results demonstrated that the synthesis of CQDs can be considered as promising for optical switching devices, bio‐scanning, and bio‐imaging for optoelectronic applications.
关键词： Z‐scan analysis,fluorescence quantum yield,CQDs,HR‐TEM,hydrothermal method
更新于2025-09-11 14:15:04
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Optical properties of chiral single-walled carbon nanotubes thin films
摘要： This work contains experimental results of optical properties for thin films containing Single-Walled Carbon Nanotubes. Thin films concerning 0.5, 1 and 2 mg of low dimension chiral (10,6) Single-Walled Carbon Nanotubes dispersed in low concentration aqueous sodium dodecyl sulfate solution (2 mL) were successfully fabricated by spin-coating technique on transparent substrates at ambient atmosphere. Optical properties of these thin films were examined using Transmission, Raman and Photoluminescence Spectroscopies. We find that investigated chiral Single-Walled Carbon Nanotubes show transmission and emission bands not only in infrared range but also ultraviolet and visible range.
关键词： Absorbance,Single-walled carbon nanotubes,Raman spectra,Photoluminescence,Decay time of photoluminescence,Quantum yield
更新于2025-09-11 14:15:04
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Spatial Heterogeneity of Cadmium Effects on Salvia sclarea Leaves Revealed by Chlorophyll Fluorescence Imaging Analysis and Laser Ablation Inductively Coupled Plasma Mass Spectrometry
摘要： In this study, for a first time (according to our knowledge), we couple the methodologies of chlorophyll fluorescence imaging analysis (CF-IA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), in order to investigate the effects of cadmium (Cd) accumulation on photosystem II (PSII) photochemistry. We used as plant material Salvia sclarea that grew hydroponically with or without (control) 100 μM Cd for five days. The spatial heterogeneity of a decreased effective quantum yield of electron transport (ΦPSII) that was observed after exposure to Cd was linked to the spatial pattern of high Cd accumulation. However, the high increase of non-photochemical quenching (NPQ), at the leaf part with the high Cd accumulation, resulted in the decrease of the quantum yield of non-regulated energy loss (ΦNO) even more than that of control leaves. Thus, S. sclarea leaves exposed to 100 μM Cd exhibited lower reactive oxygen species (ROS) production as singlet oxygen (1O2). In addition, the increased photoprotective heat dissipation (NPQ) in the whole leaf under Cd exposure was sufficient enough to retain the same fraction of open reaction centers (qp) with control leaves. Our results demonstrated that CF-IA and LA-ICP-MS could be successfully combined to monitor heavy metal effects and plant tolerance mechanisms.
关键词： effective quantum yield (ΦPSII),non-photochemical quenching (NPQ),photoprotective mechanism,photochemical quenching (qp),photosynthetic heterogeneity,phytoremediation,reactive oxygen species (ROS),bioimaging,singlet oxygen (1O2),clary sage
更新于2025-09-11 14:15:04
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Solvothermal assisted phosphate functionalized graphitic carbon nitride quantum dots for optical sensing of Fe ions and its thermodynamic aspects
摘要： A facile method has been proposed for the determination of Ferrous (Fe(II)) and Ferric (Fe(III)) ions using phosphate functionalized graphitic carbon nitride quantum dots (Ph-g-CNQDs) in an aqueous medium. The easy solvothermal procedure using oleic acid as the solvent yielded the Ph-g-CNQDs in less than 30 min. The communication among the Fe(II) and Fe(III) with Ph-g-CNQDs caused quenching of the blue Ph-g-CNQDs fluorescence signals. The Ph-g-CNQDs have been successfully characterized using X-ray diffractometry (XRD), X-ray Photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, UV–vis absorption and photoluminescence spectrophotometry. The temperature dependent behavior of the Ph-g-CNQDs was also observed and various thermodynamic parameters have also been evaluated. The Ph-g-CNQDs displayed an excellent quantum yield of 60.54% using quinine sulfate as the standard reference. The developed method has been applied to water samples collected from different sources and good recoveries were observed which entitles this method as apt for real time monitoring.
关键词： Fe(III),Quantum yield,Optical sensor,Photoluminescence,Fe(II),Phosphate functionalized g-CNQDs
更新于2025-09-11 14:15:04