查找使用阿拉丁产品的科研文献

Amplification and Dynamic Control of Circularly Polarized Luminescence in Poly (vinyl Alcohol)/CdSe@CdS Nanorod Assembly Twisted-Stacking Hetero-Structures

Li Wen,Yifan Xie,Peng Yang,Hongli Zhang,Jiahe Li,Zeyu Feng,Gang Zou

Chiroptical materials with strong and switchable circularly polarized luminescence (CPL) properties have gained considerable interest due to their feasible applications in optoelectronic devices, sensing, and information encryption. However, in most cases, their luminescence dissymmetry factor (g lum ) and figure of merit (FOM) values remain very low. Herein, a novel heterogeneous twisted-stacking structure is proposed, which endows with strong CPL amplification (a maximum of ≈15-fold enhancement) over traditional homogeneous structures and a high FOM value up to 0.11. Interestingly, their CPL performance (including the sign, magnitude, and spectral position) and the FOM values can be precisely manipulated or even inversed by simply uniaxial stretching, since the phase retardation of the anisotropic poly (vinyl alcohol) layer can be controlled. Moreover, by combining with the viologen gel electrochromic system, the in situ voltage-driven switching and patterning of the CPL signal can be successfully achieved, with low operation voltage and good cycling stability. This study provides a creative strategy for fabricating strong and electrical switchable CPL-active materials, which promise new opportunities in miniaturized smart electrochiroptical devices for future information technology.

The important role of surface ligand on CdSe/CdS core/shell nanocrystals in affecting the efficiency of H2 photogeneration from water

Ping Wang,Jie Zhang,Haili He,Xiaolong Xu,Yongdong Jin

The use of colloidal semiconductor nanocrystals (NCs), especially those with a core/shell structure, for photocatalytic hydrogen (H2) production from water is currently one of the hottest research fields. Although the ligand on the semiconductor NC surface is crucial to the optical and optoelectronic properties of the NC, the study of the ligand effect on the photocatalytic activity of H2 generation is rarely reported. Herein, we employ nearly monodispersed CdSe/CdS core/shell NCs as a model photocatalytic system, and three kinds of ligands with different numbers of functional thiol groups (i.e., poly(acrylic acid), 3-mercaptopropionic acid and 2,3-dimercaptosuccinic acid) are selected as the ligands to investigate the effect of ligand on the efficiency of H2 photogeneration. The results show that the H2 photogeneration efficiency is highly dependent on the surface ligand of the NCs, and it increases with the increase of the number of the functional thiol groups in the ligand, and correspondingly, the photoluminescence intensity and average fluorescence lifetime, which are measured by steady state and time-resolved fluorescence measurements, are decreased. The surface trap-related charge separation efficiency, which is mediated by surface coating with different ligands, is supposed to cause the distinct ligand-dependent performance in the H2 evolution.

Role of surface ligands on CdSe/CdS QDs in affecting the charge separation and photocatalytic behavior in reducing the graphene oxide

Xue Xiangxin,Chen Lei,Zhao Cuimei,Wang Hairui,Nie Ping,Chang Limin

In this paper, the photocatalytic behavior of CdSe/CdS quantum dots (QDs) in reducing the graphene oxide (GO) with different surface ligands was investigated. Here, three surface ligands of different functional groups (oleic acid, poly (acrylic acid polymers) and S 2− ) were selected to study the influence of surface ligands on photocatalytic behavior of the CdSe/CdS QDs. Meanwhile, the obtained samples can be used as photocatalyst, and the photocatalytic activity was evaluated by photodegrading a methylene blue solution. It turned out that the QDs–S 2− –GO sample showed the highest photocatalytic activity under visible-light irradiation. Different surface ligand has different influence on the charge separation efficiency, which has different influence on photocatalytic behavior. The results show that the photocatalytic behavior is highly dependent on the electron attracting ability of the surface ligands on the CdSe/CdS QDs. Finally, a possible photocatalytic mechanism is proposed.

High-efficiency CdSe/CdS nanorod–based red light–emitting diodes

Yanbin Zhang,Fengjuan Zhang,Hongzhe Wang,Lei Wang,Fangfang Wang,Qingli Lin,Huaibin Shen,Lin Song Li

In this paper, we report the synthesis, the structural and optical characterization of CdSe/CdS//CdS nanorods (NRs) and their exploitation in nanorod-based light-emitting diodes (NR-LEDs). Two kinds of NRs of CdSe/CdS and CdSe/CdS//CdS were incorporated into the structure of solution-processed hybrid NR-LEDs. Compared to CdSe/CdS, the efficiencies of CdSe/CdS//CdS NR-based LEDs are overwhelmingly higher, specifically showing unprecedented values of peak current efficiency of 19.8 cd/A and external quantum efficiency of 15.7%. Such excellent results are likely attributable to a unique structure in CdSe/CdS//CdS NRs with a relatively high quantum yield, thick CdS outer shell, and rod structure which minimize nonradiative energy transfer between closely packed NRs in emitting layer.

An electrochemiluminescence sensor based on CdSe@CdS-functionalized MoS2 and a GOD-labeled DNA probe for the sensitive detection of Hg(II)

Zhang-Jin He,Tian-Fang Kang,Li-Ping Lu,Shui-Yuan Cheng

In this study, a novel electrochemiluminescence (ECL) biosensor based on a CdSe@CdS quantum dot (QD)-functionalized MoS2-modified electrode was developed for the sensitive detection of mercury ions. Polycationic poly(diallyldimethylammonium chloride) (PDDA) and negatively charged QDs were adsorbed on the surface of MoS2, in sequence, to form the QD–PDDA–MoS2 composites, which were employed as matrices for immobilizing thymine-rich DNA sequences (DNA1). The gold nanoparticles (AuNPs) were combined with another type of thymine-rich DNA sequences (DNA2) and glucose oxidase (GOD) to prepare the GOD–AuNP–DNA2 conjugates. The composites were characterized via UV-visible absorption spectroscopy, fluorescence and transmission electron microscopy. A thymine–Hg2+–thymine complex was formed through Hg2+ mismatching with DNA1 and DNA2. GOD was, therefore, modified onto the electrode surface. GOD catalyzed the reduction of dissolved oxygen by glucose to produce hydrogen peroxide, which was a co-reactant of the QDs. The electrochemiluminescence signal of the biosensor increased linearly with the increase in the Hg2+ concentration over the range from 1.0 × 10−12 to 1.0 × 10−6 M with a detection limit of 1 × 10−13 M. The reproducibility, stability and specificity of the biosensor was also studied. The biosensor was used to determine Hg2+ in a real water sample and satisfactory results were obtained.

To Battle Surface Traps on CdSe/CdS Core/Shell Nanocrystals: Shell Isolation versus Surface Treatment

Chaodan Pu,Xiaogang Peng

Electronic traps at the inorganic–organic interface of colloidal quantum dots (QDs) are detrimental to their luminescent properties. Several types of interface traps were identified for single-crystalline CdSe/CdS core/shell QDs, which were all found to be extrinsic to either the core/shell structure or their optical performance. The electron traps—presumably excess or unpassivated Cd surface sites—are shallow ones and could be readily isolated from the electron wave function of the excitons with more than ∼2 monolayers of CdS shell. There were two identifiable deep hole traps within the bandgap of the QDs, i.e., the surface adsorbed H2S and unpassivated surface S sites. The surface adsorbed H2S could be removed by either degassing processes or photochemical decomposition of H2S without damaging the QDs. The unpassivated surface S sites could be removed by surface treatment with cadmium carboxylates. Understanding of the surface traps enabled establishment of new phosphine-free synthetic schemes for either single-precursor or successive-ion-layer-adsorption-and-reaction approach, which yielded CdSe/CdS core/shell QDs with near-unity photoluminescence quantum yield and monoexponential photoluminescence decay dynamics with 2–10 monolayers of CdS shell.

An electrochemiluminescence sensor based on CdSe@CdS functionalized MoS2 and hemin/G-quadruplex-based DNAzyme biocatalytic precipitation for sensitive detection of Pb(II)

Xiao-Li Du,Tian-Fang Kang,Li-Ping Lu,Shui-Yuan Cheng

A novel electrochemiluminescence (ECL) biosensor based on CdSe@CdS quantum dots (QDs) functionalized MoS2 modified electrode was developed for sensitive detection of Pb(II) using HRP-mimicking DNAzyme biocatalytic precipitation (BCP) for ECL signal quenching. Polycationic poly(diallyldimethylammonium chloride) (PDDA) and negatively charged QDs were adsorbed on the surface of MoS2, in sequence, to form the MoS2–QDs composites, which were employed as a matrix for the immobilization of the G-rich DNA strand, i.e., T30695. The MoS2–QDs were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, energy dispersive spectrometry, transmission electron microscopy, and field emission scanning electron microscopy. CdSe@CdS QDs can produce an ECL signal using 0.1 M K2S2O8 as a co-reactant. T30695 can combine with Pb(II) ions to form a stable parallel G-quadruplex. The G-quadruplex can further combine with hemin to form DNAzyme, which can catalyze H2O2 and oxidize 4-chloro-1-naphthol (4-CN) to produce an insoluble precipitation of benzo-4-chlorohexadienone on the surface of the sensor. When the concentration of Pb(II) in the solution was increased, more of DNAzyme was generated and subsequently more 4-CN molecules were oxidized catalytically, leading to a decrease of the ECL signal. Using this quenching strategy, the ECL signal of the biosensor was linearly dependent on the logarithm of the Pb(II) concentration ranging from 1.0 × 10−15 to 1.0 × 10−11 M with a detection limit of 0.98 f M. The stability and selectivity of the sensor were also investigated. The sensor was applied in the determination of Pb(II) in the real water samples and satisfactory results were obtained.

Water Effects on Colloidal Semiconductor Nanocrystals: Correlation of Photophysics and Photochemistry

Zhuang Hu,Yufei Shu,Haiyan Qin,Xiaofei Hu,Xiaogang Peng

With high-quality CdSe/CdS core/shell nanocrystals as the main model system and under a controlled atmosphere, responses of photoexcited semiconductor nanocrystals to two active species (water and/or oxygen) in an ambient environment are studied systematically. Under photoexcitation, although high-quality semiconductor nanocrystals in either thin solid films or various solutions have a near-unity photoluminescence quantum yield, there is still a small probability (∼10–5 per photon absorbed) to be photoreduced by the water molecules efficiently accumulated in the highly hydrophilic nanocrystal–ligands interface. The resulting negatively charged nanocrystals are the starting point of most photophysical variations, and the hydroxyl radical─key photo-oxidation product of water─plays the main role for initiating various photochemical processes. Depending on the supplementation of water to the interface, accessibility to oxygen, photoirradiation power, type of matrices, type of measurement schemes, and solubility of nanocrystals in the solution, various photophysical/photochemical phenomena─either reported or not reported in the literature─are reproducibly observed. Results confirm that photophysical properties and photochemical reactions can be well-correlated, offering a unified and unique basis for fundamental studies and the design of processing techniques in industry.

Type-I CdSe@CdS@ZnS Heterostructured Nanocrystals with Long Fluorescence Lifetime

Yuzhe Wang,Yueqi Zhong,Jiangzhi Zi,Zichao Lian

Conventional single-component quantum dots (QDs) suffer from low recombination rates of photogenerated electrons and holes, which hinders their ability to meet the requirements for LED and laser applications. Therefore, it is urgent to design multicomponent heterojunction nanocrystals with these properties. Herein, we used CdSe quantum dot nanocrystals as a typical model, which were synthesized by means of a colloidal chemistry method at high temperatures. Then, CdS with a wide band gap was used to encapsulate the CdSe QDs, forming a CdSe@CdS core@shell heterojunction. Finally, the CdSe@CdS core@shell was modified through the growth of the ZnS shell to obtain CdSe@CdS@ZnS heterojunction nanocrystal hybrids. The morphologies, phases, structures and performance characteristics of CdSe@CdS@ZnS were evaluated using various analytical techniques, including transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy, fluorescence spectroscopy and time-resolved transient photoluminescence spectroscopy. The results show that the energy band structure is transformed from type II to type I after the ZnS growth. The photoluminescence lifetime increases from 41.4 ns to 88.8 ns and the photoluminescence quantum efficiency reaches 17.05% compared with that of pristine CdSe QDs. This paper provides a fundamental study and a new route for studying light-emitting devices and biological imaging based on multicomponent QDs.

Oxygen Stabilizes Photoluminescence of CdSe/CdS Core/Shell Quantum Dots via Deionization

Zhuang Hu,Shaojie Liu,Haiyan Qin,Jianhai Zhou,Xiaogang Peng

By taking advantage of well-defined spectroscopic signatures of high-quality CdSe/CdS core/shell QDs, the effects of oxygen on photoluminescence (PL) of QDs were studied systematically and quantitatively at both single-dot and ensemble (on substrate and in solution) levels, which reveals a unified yet simple picture. With a sufficient amount of oxygen in the system during photoexcitation, the core/shell QDs in all forms would be deionized timely from the photogenerated and inefficient trion state back to the efficient single-exciton state, with superoxide radicals as the reduction product of oxygen. Under a given excitation power, rates of both spontaneous deionization and photodeionization channels increased by increasing the oxygen pressure, but photoionization of the QDs was barely affected by the oxygen pressure. While stabilizing PL by oxygen was identified for both CdSe plain core and CdSe/CdS core/shell QDs, irreversible photocorrosion was only observed for CdSe plain core QDs, suggesting the importance of high-quality epitaxial shells for QDs in various applications.

Ultrapure Green Light-Emitting Diodes Based on CdSe/CdS Core/Crown Nanoplatelets

Zuoliang Wen,Chaojian Zhang,Ziming Zhou,Bing Xu,Kai Wang,Kie Leong Teo,Xiao Wei Sun

Enhanced Photochemical Stability of CdSe/CdS Quantum Dots Capped by Imidazolium-Based Ionic Liquids

Zhang Hucheng,Qiao Haixia,Li Fangfang,Xu Dong,Wang Jianji

The novel thiol-functionalized ionic liquids (ILs), 1-(10-mercaptodecyl)-3-methylimidazolium chloride ([HS-C10mim]Cl) and 1-(4-mercaptobutyl)-3-methylimidazolium chloride ([HS-C4mim]Cl), were synthesized by introducing thiol groups onto the alkyl chains in imidazolium-based ILs. The ILs exhibit strong affinity toward CdSe/CdS quantum dots (QDs), and can readily transfer the QDs from organic phases to aqueous phase. The IL-capped CdSe/CdS QDs are extremely soluble in water, and their photochemical stability was measured by absorption spectra. It is shown that the [HS-C10mim]Clcapped QDs in water present much better anti-photooxidation than [HS-C4mim]Cl-capped those. The measurements of Zeta potential and hydrodynamic diameter reveal that the enhanced mechanism of [HS-C10mim]Cl depends mainly on the specific physico-chemical properties of the ILs. In particular, CdSe/CdS QDs with high surface potential, small hydrodynamic diameter, and optimal photochemical stability can be harvested by the solubilization of free [HS-C10mim]Cl in ligand shells of the QDs.