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Synthesis of Glutathione Modified CdSe Quantum Dots and Its Application in Determination of Trace Hg2+ Ions
摘要： The water-soluble glutathione (GSH) modified CdSe quantum dots (QDs) were prepared. Results show that the optimum NaBH4:Se:(Cd2+): glutathione molar ratio is obtained to be 3:1:3:9. Meanwhile, the glutathione modified CdSe quantum dots synthesized by the optimum process have a single face centered cubic phase. It is found that the fluorescence quenching occurred as Hg2+ ions interact with glutathione modified CdSe quantum dots. Hg2+ ions can be determined in the concentration range of 0.3-15 μg/L, which is proposed to determine the trace quantities of Hg2+ ions as fluorescence probe.
关键词： Glutathione,Quantum dots,Fluorescence probe,CdSe
更新于2025-09-16 10:30:52
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Identifying Clusters and/or Small-Size Quantum Dots in Colloidal CdSe Ensembles with Optical Spectroscopy
摘要： It is well-known that optical absorption and photoluminescence (PL) provide information that is sensitive to the size and size distribution of colloidal binary semiconductor quantum dots (QDs). To explore the nature of reaction products, clusters, and/or small-size QDs, we show that it is important to perform as well photoluminescence excitation (PLE) spectroscopy. For two non-hot-injection reactions of cadmium oleate (Cd(OA)2) and selenium (Se) in 1-octadecene (ODE), we show that sequentially extracted products displayed a similar apparent red shift in both absorption and PL with a full width at half-maximum (fwhm) of ～30 nm. We demonstrate that one reaction (with the presence of diphenyl phosphine (HPPh2)) produced multiple types of clusters (with slightly different optical properties) in one ensemble, while the other reaction (without HPPh2) yielded primarily small-size QDs. Our findings provide evidence for the probable existence of clusters within small-size CdSe QD products, the existence of which complicates the size determination of small-size CdSe QDs.
关键词： optical absorption,photoluminescence,photoluminescence excitation spectroscopy,clusters,CdSe quantum dots
更新于2025-09-16 10:30:52
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Spectroscopic monitoring of the evolution of size and structural defects in kinetic growth of CdSe quantum dots
摘要： We report here on the exciton-phonon coupling and role of trap states formed at the interface of structural dislocations in CdSe quantum dots (QDs) synthesized by kinetic growth method. Even though non-luminescing, our studies recognize their signatures in the temperature dependent photoluminescence characteristics of lowest QD excitonic state and have some useful implications for structural quality of thus synthesized QDs. We have explained the observed temperature dependence of PL intensity in terms of a simple model taking account of different radiative and nonradiative recombination processes as well as carrier trapping/detrapping and determined the depth of potential well formed due to such long range defects. Our studies indicate the presence of such defect states only in QD samples size sorted by aliquoting at intermediate intervals during the reaction and do not appear when the reaction proceeds uninterrupted.
关键词： Temperature dependent photoluminescence,Exciton-phonon coupling,Thermal escape,CdSe Quantum Dots
更新于2025-09-16 10:30:52
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Hybrid CdSe/CsPbI <sub/>3</sub> quantum dots for interface engineering in perovskite solar cells
摘要： Hybrid CdSe/CsPbI3 quantum dots (QDs) are selected for incorporation between the perovskite film and the hole transport layer (HTL). Owing to the high absorption coefficient and the suitable band gap of CsPbI3, an optimized energy level structure can be expected. Besides, energy transfer could be realized due to the overlap between the emission spectrum of CdSe QDs and the excitation spectrum of CsPbI3 QDs. Hence, CdSe/CsPbI3 QDs can serve as an interface layer to promote interfacial charge extraction and enhance light harvesting ability simultaneously. Compared with pristine perovskite solar cells (PSCs), hybrid CdSe/CsPbI3 QD incorporated PSCs achieve 21% enhancement in power conversion efficiency (PCE). The enhancement of PCE can be ascribed to the ultrafast charge carrier dynamics and F?rster resonance energy transfer (FRET) effect. The design of hybrid CdSe/CsPbI3 QDs offers an alternative method for interfacial engineering to enhance optical properties and facilitate the charge transport process in PSCs.
关键词： interface engineering,charge transport,perovskite solar cells,Hybrid CdSe/CsPbI3 quantum dots,F?rster resonance energy transfer
更新于2025-09-16 10:30:52
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Strain Effects on the Band Gap and Diameter of CdSe Core and CdSe/ZnS Core/Shell Quantum Dots at Any Temperature
摘要： We present the results of an experimental study about strain effects on the core band gap and diameter of spherical bare CdSe core and CdSe/ZnS core/shell quantum dots (QDs) synthesized by using a colloidal technique at varying temperatures. Structural characterizations were made by using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques. Optical characterizations were made by using UV-Vis absorption and fluorescence emission spectroscopies. The XRD analysis suggests that the synthesized bare CdSe core and CdSe/ZnS core/shell QDs have zinc blende crystal structure. HRTEM results indicate that the CdSe core and CdSe/ZnS QDs have average particle sizes about 3.50 nm and 4.84 nm, respectively. Furthermore, compressive strain causes an increase (decrease) in the core band gap (diameter) of spherical CdSe/ZnS core/shell QDs at any temperature. An elastic strain-modified effective mass approximation (EMA) predicts that there is a parabolic decrease (increase) in the core band gap (diameter) of QDs with temperature. The diameter of spherical bare CdSe core and CdSe/ZnS core/shell QDs calculated by using the strain-modified EMA, with core band gap extracted from absorption spectra, are in excellent agreement with the HRTEM data.
关键词： diameter,quantum dots,band gap,CdSe,strain effects,CdSe/ZnS,temperature
更新于2025-09-12 10:27:22
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Atomically-thin population of colloidal CdSe nanoplatelets: growth of rolled-up nanosheets and strong circular dichroism induced by ligand exchange
摘要： Colloidal two-dimensional cadmium chalcogenides nanoplatelets have recently emerged as a class of semiconductor nanoparticles with the narrowest emission and absorption excitonic bands that are of interest for optical applications. Here, we have developed a synthesis protocol for 2.5 monolayers (ML) thick CdSe nanosheets as a single population. We found that a two-step synthesis in the presence of water promoted the growth of atomically-thin nanosheets with high structural and morphological perfection. Using seeded-growth technique, we extended the lateral size of nanosheets up to 400 nm, which led to the formation of multiwall rolled-up nanostructures. Ligand exchange of native oleic acid, attached to Cd-rich (001) planes, with achiral thioglycolic acid and chiral N-acetylcysteine retains a scroll-like morphology of nanosheets, in contrast to thicker 3.5 ML population. A reorientation from the [110] to [100] folding direction was found during the change from an achiral to a chiral ligand. In the case of ligand exchange with chiral N-acetyl-L- or D-cysteine, we demonstrated that 2.5 ML CdSe nanosheets with 400 nm lateral size have circular dichroism with dissymmetry g-factor up to 3?10-3. Strong circular dichroism found for colloidal CdSe nanosheets makes them a promising candidate for polarization-enabled applications, while the growth protocol of the thinnest CdSe nanosheets enriches the known synthesis methods of a set of CdSe nanoplatelet populations.
关键词： nanoplatelets,colloidal,circular dichroism,CdSe,ligand exchange
更新于2025-09-12 10:27:22
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On-demand Milifluidic Synthesis of Quantum Dots in Digital Droplet Reactors
摘要： Colloidal quantum dots (QDs) offer dramatic potential due to their size-dependent optical properties. Lack of facile synthesis methods for precise and reproducible size and composition, however, present an extant barrier to their widespread use. Here we report the use of droplet microfluidics for the simple and highly reproducible synthesis of cadmium sulfide (CdS) and cadmium selenide (CdSe) QDs without the use of harsh solvents and in ambient conditions. Our approach uses a liquid-liquid barrier between two immiscible liquids to generate a digital droplet reactor. This reaction droplet is easily controlled and manipulated and offers enhanced mixing when coupled to a helical mixer, resulting in a significant reduction in size distribution compared to benchtop procedures. Furthermore, QD characteristics have modeled and predicted based on the parameters of the microfluidic device. We believe this method overcomes the current manufacturing challenges with synthesizing nanostructures, which is required for the next generation of nanosensors.
关键词： CdS,CdSe,quantum dots,microfluidics,nanosensors
更新于2025-09-12 10:27:22
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Effect of energy transfer on the optical properties of surface-passivated perovskite films with CdSe/ZnS quantum dots
摘要： Surface passivation is an effective method to protect the surfaces and improve the luminescence properties of perovskite (PS) films. CdSe/ZnS core-shell quantum dots (QDs) have been employed for surface passivation of PS films because of their size-dependent tunable bandgaps. Herein, the energy transfer (ET) behavior of CH3NH3PbI2Br PS films covered with CdSe/ZnS QDs (QD/PS hybrid structures) is characterized by using photoluminescence (PL) and time-resolved PL spectroscopy. The PL decay time and the integrated PL intensity of the QD/PS hybrid structure increase compared with those of the bare PS films, owing to ET from the QDs to the PS and reduced charge traps. The ET efficiency increases from ~7% to 63% for the QD/PS hybrid structure when the core diameter of the QDs decreases from 6.5 to 2.7 nm, respectively. This can be explained by the charge transfer rate enhancement due to the control of energy level alignment of QDs. These results allow us to understand fundamental mechanisms such as ET from QDs to PS films as a function of the size of the QD.
关键词： CdSe/ZnS quantum dots,perovskite films,energy transfer,photoluminescence,surface passivation
更新于2025-09-12 10:27:22
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Electronic coupling in colloidal quantum dot molecules; the case of CdSe/CdS core/shell homodimers
摘要： Coupled colloidal quantum dot molecules composed of two fused CdSe/CdS core/shell sphere monomers were recently presented. Upon fusion, the potential energy landscape changes into two quantum dots separated by a pretuned potential barrier with energetics dictated by the conduction and valence band offsets of the core/shell semiconductors and the width controlled by the shell thickness and the fusion reaction conditions. In close proximity of the two nanocrystals, orbital hybridization occurs, forming bonding and antibonding states in analogy to the hydrogen molecule. In this study, we examine theoretically the electronic and optical signatures of such a quantum dot dimer compared to its monomer core/shell building-blocks. We examine the effects of different core sizes, barrier widths, different band offsets, and neck sizes at the interface of the fused facets on the system wave-functions and energetics. Due to the higher effective mass of the hole and the large valence band offset, the hole still essentially resides in either of the cores, breaking the symmetry of the potential for the electron as well. We found that the dimer signature is well expressed in a red shift of the band gap both in absorption and emission, in slower radiative lifetimes and in an absorption cross section which is significantly enhanced relative to the monomers at energies above the shell absorption onset, while remains essentially at the same level near the band-edge. This study provides essential guidance to predesign of coupled quantum dot molecules with specific attributes which can be utilized for various new opto-electronic applications.
关键词： optical signatures,CdSe/CdS core/shell,electronic coupling,colloidal quantum dot molecules,quantum dot dimer
更新于2025-09-12 10:27:22
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Semiconductor Quantum Dots Are Efficient and Recyclable Photocatalysts for Aqueous PET-RAFT Polymerization
摘要： This Letter describes the use of CdSe quantum dots (QDs) as photocatalysts for photoinduced electron transfer reversible addition?fragmentation chain transfer (PET-RAFT) polymerization of a series of aqueous acrylamides and acrylates. The high colloidal solubility and photostability of these QDs allowed polymerization to occur with high efficiency (>90% conversion in 2.5 h), low dispersity (PDI < 1.1), and ultralow catalyst loading (<0.5 ppm). The use of protein concentrators enabled the removal of the photocatalyst from the polymer and monomer with tolerable metal contamination (8.41 ug/g). These isolated QDs could be recycled for four separate polymerizations without a significant decrease in efficiency. By changing the pore size of the protein concentrators, the QDs and polymer could be separated from the remaining monomer, allowing for the synthesis of block copolymers using a single batch of QDs with minimal purification steps and demonstrating the fidelity of chain ends.
关键词： block copolymers,CdSe quantum dots,photocatalysts,aqueous acrylamides,acrylates,protein concentrators,PET-RAFT polymerization
更新于2025-09-12 10:27:22