Investigation on Exciton Relaxation Kinetics of ZnCuInS/ZnSe/ZnS Quantum Dots by Time-Resolved Spectroscopy Techniques

Based on the location of bromine substituents and conjugation matrix, a new substituent po-sition index ⁰X not only was defined, but also molecular shape indexes K_m and electronega-tivity distance vectors M_m of diphenylamine and 209 kinds of polybrominated diphenylamine (PBDPA) molecules were calculated. Then the quantitative structure-property relationships (QSPR) among the thermodynamic properties of 210 organic pollutants and ⁰X、K₃、M₂₉、M₃₆ were founded by Leaps-and-Bounds regression. Using the four structural parameters as input neurons of the artificial neural network, three satisfactory QSPR models with network structures of 4:21:1, 4:24:1, and 4:24:1 respectively, were achieved by the back-propagation algorithm. The total correlation coefficients R were 0.9999, 0.9997, and 0.9995 respectively and the standard errors S were 1.036, 1.469, and 1.510 respectively. The relative mean deviation between the predicted value and the experimental value of S^?,Δ_fH^? and Δ_fG^? were 0.11%, 0.34% and 0.24% respectively, which indicated that the QSPR models had good stability and superior predictive ability. The results showed that there were good nonlinear correlations between the thermodynamic properties of PBDPAs and the four structural pa-rameters. Thus, it was concluded that the ANN models established by the new substituent position index were fully applicable to predict properties of PBDPAs.     

飞秒荧光亏蚀光谱技术研究液相体系取向弛豫

溶液中分子的快速弛豫过程直接反映了溶液中溶质和周围溶剂分子间的相互作用[1-3]．在液相体系中分子取向通常是随机分布的．当溶质分子被线偏振光激发至激发态时,其分子取向将由原来各向同性的球形分布瞬间变成各向异性的椭球分布．由于溶质分子周围大量溶剂分子的存在,通过二者之间相互作用,激发态溶质分子在一定方向上的取向优势将很快弛豫掉．这种溶液中的取向弛豫过程通常是几个到几百皮秒[1-3]．     

Ligand-Controlled Growth of ZnSe Quantum Dots in Water during Ostwald Ripening

A strong ligand effect was observed for the aqueous-phase growth of ZnSe quantum dots (QDs) in the Ostwald ripening (OR) stage. The QDs were made by injecting Se monomer at room temperature followed by a ramp to 100 °C. The ramp produced a second, more gradual increase in the concentrations of both Zn and Se monomers fed by the dissolution of QDs below the critical size. The dissolution process was followed using measurements of the mass of Zn in QDs and in the supernatant by inductively coupled plasma optical emission spectroscopy (ICP-OES). Despite the flux of monomers, there was little growth in the QDs of average size based on UV-vis absorption spectra, until the temperature reached 100 °C, when there was a period of rapid growth followed by a period of linear growth. The linear growth stage is the result of OR as the total mass of Zn in QDs and in the solvent remained constant. The growth data were fit to a continuum model for the limiting case of surface reaction control. The rate is proportional to the equilibrium coefficient for ligand detachment from the QD surface. The ligand 3-mercaptopropionic acid (MPA) was the most tightly bound to the surface and produced the lowest growth rate of (1.5-2) × 10(-3) nm/min in the OR stage, whereas thiolactic acid (TLA) was the most labile and produced the highest growth rate of 3 × 10(-3) nm/min. Methyl thioglycolate (MTG) and thioglycolic acid (TGA) produced rates in between these values. Ligands containing electron-withdrawing groups closer to the S atom and branching promote growth, whereas longer, possibly bidendate, ligands retard it. Mixed ligand experiments confirmed that growth is determined by ligand bonding strength to the QD. Photoluminescence spectroscopy showed that the more labile the ligand, the more facile the repair of surface defects during the exposure of the QDs to room light.     

脂质体包覆CdSe/ZnSe核－壳量子点

本文提出了一种利用脂质体包覆量子点的方法。这种脂质体包覆的方法可以使量子点溶于水。被脂质体包覆的CdSe/ZnSe量子点仍具有很强的荧光，其荧光强度与未包覆的CdSe/ZnSe量子点处于同一数量级且具有很好的荧光稳定性。这种脂质体包覆的量子点有很好的生物相容性，利用它为荧光标记物，制备了鼠单克隆抗体CD95的免疫检测传感器。     

硫脲修饰ZnSe:Cu量子点的水相合成及荧光特性

以3-巯基丙酸为稳定剂在水相中合成了Cu掺杂的ZnSe量子点(QDs), 并利用硫脲(CH₄N₂S)对其进行表面修饰, 制备出核壳结构的ZnSe:Cu/ZnS 量子点. 制得的量子点呈闪锌矿结构, 尺寸约为5 nm, 有较好的分散性, 其荧光发射峰在460 nm左右. 经CH₄N₂S修饰后, 量子点表面形成了宽禁带的ZnS包覆层, 将电子和空穴限域在了ZnSe:Cu 核内, 减少了表面发生非辐射复合的载流子, 显著提高了量子点的荧光强度. 与Na₂S、硫代乙酰胺(TAA)等常用硫源相比, 以CH₄N₂S为硫源制得的ZnSe:Cu/ZnS 量子点壳层厚度可控, 表面钝化效果更好, 显示出更佳的荧光效率和稳定性. ZnSe:Cu/ZnS 量子点经过紫外线照射后消除了表面的悬空键, 进一步提高了其量子产率, 最终获到了具有较好荧光性质的ZnSe:Cu/ZnS量子点.     

Excited State Relaxation and Stabilization of Hydrogen Terminated Silicon Quantum Dots

Silicon is the leading semiconductor material in microelectronic industry. Owing to the large surface to volume ratio, low-dimensional Si nanostructures, for instance, silicon quantum dots exhibit diverse electronic and optical properties. Passivating the surface of Si nanostructures by a suitable species is thereby required to stabilize and engineer the dot properties in different environment. Recent theoretical advances in the investigation of the excited state properties of silicon quantum dots (QDs) are reviewed in this article. The theoretical calculations reveal that the excited state relaxation is prevalent in hydrogenated silicon nanoparticles. Stokes shift due to structure relaxation in the excited state varies with the particle size. It is therefore desirable to minimize Stokes shift for the purpose of maximizing its quantum yield or efficiency in photoluminescence applications. Consequently, surface functionalization by a suitable species turns out to be the most effective avenue. Determination of proper passivating agent is of outmost importance to satisfy the practical necessity. All these intermingled factors are briefly addressed in this article.     

Femtosecond Excitonic Relaxation Dynamics of Perovskite on Mesoporous Films of Al2O3 and NiO Nanoparticles

The excitonic relaxation dynamics of perovskite adsorbed on mesoporous thin films of Al₂O₃ and NiO upon excitation at 450 nm were investigated with femtosecond optical gating of photoluminescence (PL) via up‐conversion. The temporal profiles of emission observed in spectral region 670–810 nm were described satisfactorily with a composite consecutive kinetic model and three transient components representing one hot and two cold excitonic relaxations. All observed relaxation dynamics depend on the emission wavelength, showing a systematic time–amplitude correlation for all three components. When the NiO film was employed, we observed an extent of relaxation proceeding through the non‐emissive surface state larger than through the direct electronic relaxation channel, which quenches the PL intensity more effectively than on the Al₂O₃ film. We conclude that perovskite is an effective hole carrier in a p‐type electrode for NiO‐based perovskite solar cells showing great performance.     

硒化镉量子点膜的拉曼光谱及拉曼成像分析

研究了CdSe量子点膜的Raman光谱,发现CdSe量子点的横模(TO)振动活性较强,表面模(SO)、纵模(LO)振动不明显。比较了量子点、氧化三辛基膦及十六胺的Raman光谱,证明量子点表面大部分区域被十六胺及二辛胺修饰。在此基础上,对量子点膜的TO模振动及C-H弯曲振动峰进行了Raman成像分析,并与明场图像进行了对比,表明拉曼成像信号对量子点膜的表面变化非常敏感。     

pH-sensitive Photoluminescence of CdSe/ZnSe/ZnS Quantum Dots in Human Ovarian Cancer Cells

The photoluminescence of mercaptoacetic acid (MAA)-capped CdSe/ZnSe/ZnS semiconductor nanocrystal quantum dots (QDs) in SKOV-3 human ovarian cancer cells is pH-dependent, suggesting applications in which QDs serve as intracellular pH sensors. In both fixed and living cells the fluorescence intensity of intracellular MAA-capped QDs (MAA QDs) increases monotonically with increasing pH. The electrophoretic mobility of MAA QDs also increases with pH, indicating an association between surface charging and fluorescence emission. MAA dissociates from the ZnS outer shell at low pH, resulting in aggregation and loss of solubility, and this may also contribute to the MAA QD fluorescence changes observed in the intracellular environment.     

Application of CdTe/ZnSe Quantum Dots in In Vitro Imaging of Chicken Tissue and Embryo

The present work is aimed to synthesize CdTe/ZnSe core/shell quantum dots (QDs) in an easy way and to explore the possibilities of its application in in vitro imaging of chicken tissue and embryo. The QDs were prepared using microwave irradiation with different temperatures, which is a very easy and less time‐consuming method. Subsequently, these QDs were characterized by spectrofluorimetry, Transmission Electron Microscopy, X‐ray fluorescence analysis and Dynamic Light Scattering measurement. A blueshifting of the emission was found when ZnSe was deposited on CdTe QDs. The QDs showed its fluorescence emission quantum yields up to 25%. They were applied into chicken embryos and breast muscle tissues to study their efficiency in in vitro imaging. All the QDs of different color were able to visualize in in vitro imaging. The highest fluorescence intensity was detected in the case of red QDs prepared at 100°C. The green and red QDs were possible to detect up to the depth of 3 and 4 mm of the tissue, respectively.     

Study on the Interaction between CdSe Quantum Dots and Bovine Serum Albumin with Ultraviolet Visible Absorption Spectroscopy

QDs (also called semiconductor nanocrystallines) were attracted considerable attention in the past decade1, 2. They have been used as luminescent probes in biology, medicine and more recently in analytical chemistry3-5. The interaction between QDs and ino…     

Study of Streptavidin-Modified Quantum Dots by Capillary Electrophoresis

Great boom of nanotechnologies impacts almost all areas of science and therefore detail understanding of the properties of nanomaterials as well as their interaction abilities is required. Surface modification and functionalization of nanoparticles is of a great interest due to the wide range of applications in the area of nanomedicine, nanobiology, and/or biochemistry. In this study, CdTe QDs were synthesized using microwave reactor and their surface was modified by streptavidin to ensure further suitability for bioconjugation with biotin-labelled oligonucleotides. For characterization of the synthesized QDs and for monitoring of the interaction with the oligonucleotide, capillary and gel electrophoresis was used. Moreover, complementary advantages of absorption (CE–UV) and laser-induced fluorescence detection (CE–LIF) were exploited. Comparison the electrophoretic mobilities obtained for streptavidin-modified QDs by CE–LIF (?9.87 × 10^?9 m²/V/s) and by CE–UV (?10.02 × 10^?9 m²/V/s) was in a good agreement enabling us to identify the peak of streptavidin-modified QDs in the CE–UV electropherogram containing also the peak of unreacted streptavidin. Subsequent conjugation of streptavidin-modified QDs with two model biotinylated oligonucleotides (BCL-2 and HBV) led to formation of the complex represented in the electropherograms as a very sharp peak. This peak height increased with time for 15.5 and 27 mAU using BCL-2 oligonucleotide and HBV oligonucleotide, respectively during 30 min interaction.     

Synthesis of Black Phosphorus Quantum Dots with High Quantum Yield by Pulsed Laser Ablation for Cell Bioimaging

Black phosphorus quantum dots (BPQDs), with an average diameter of about 6 nm and a height of about 1.1 nm, are successfully synthesized by means of a pulsed laser ablation (PLA) method in isopropyl ether (IPE) solvent. The photoluminescence PL quantum yield of the as‐prepared sample is as high as 20.7 %, which is 3 times that of BPQDs prepared by means of probe ultrasonic exfoliation (approximately 7.2 %). The stable and blue–violet PL emission of the BPQDs is observed. It can be elucidated that electrons transit from the LUMO energy level to the HOMO energy level, as well as energy levels below the HOMO (H1 and H2). In addition, BPQDs are also utilized in bioimaging in HeLa cells, showing an intense and stable PL signal and excellent biocompatibility. Hence, this work indicates that the obtained BPQDs with high quantum yield and stable PL emission have great potential for biomedical applications, including biolabeling, bioimaging, and drug delivery.     

Graphdiyne:Structure of Fluorescent Quantum Dots

Graphdiyne (GDY) as an emerging two‐dimensional carbon allotrope exhibits excellent performance in energy chemistry, catalytic chemistry, optoelectronics, electronics, etc. because of the unique structure combining an sp‐ and sp²‐hybrid carbon network. However, the poor solubility of pristine GDY is a major obstacle to its applications in many fields. Proposed here is a facile strategy to control the preparation of GDY quantum dots (GDY‐Py QDs), in which pyrene groups are covalently linked to GDY by using a Sonogashira cross‐coupling reaction. The as‐prepared GDY‐Py QDs, with an average diameter of about 3±0.1 nm, show superior dispersibility in many organic solvents and water. The GDY‐Py QDs display not only bright fluorescent with a high relative quantum yield (QY) of 42.82 %, but they are also well‐behaved as contrast agents in cell imaging. The GDY‐Py QDs are bestowed with high stability and non‐cytotoxicity, and exhibit long fluorescent times, and have potential for optical imaging and biomedical applications.     

不同环境因子作用下水溶性CdTe量子点的生长动力学研究

以硫普罗宁为稳定剂,水热法制备了水溶性CdTe量子点,系统研究了回流时间、反应物配比、pH值、反应温度和电解质种类等环境因子对量子点生长动力学及光物理性质的影响。结果表明,溶液的pH值及反应物配比对CdTe量子点的光物理性质均有重要影响。优化条件后,回流5 h可得到发射峰位于550 nm的CdTe量子点,其荧光量子效率高达52%;在氯化钠作用下,量子点生长加快,即高浓度氯化钠会减弱溶液中粒子间静电排斥,促进离子扩散,有利于量子点的生长;添加苯磺酸钠会抑制量子点的生长,有利于制备高荧光量子效率的小尺寸CdTe量子点。     

从量子点的角度审视碳点的研究进展

碳点不仅具有类似于传统量子点的强发光和小尺寸特性,还表现出传统量子点无法比拟的水相分散性和生物相容性等优势.作为量子点领域的一个新兴分支,碳点的结构、合成化学和光电性质与传统量子点显著不同,也为量子点的发展提供了新的机遇和挑战.随着碳点领域的迅速发展和不断深化,越来越有必要在一些基本概念上与传统量子点比较,并从传统量子点的角度澄清碳点的独特特征和关键挑战.本综述主要聚焦于基本结构、合成化学、光学性质和应用研究等四个方面,从传统量子点基础概念的角度来重新审视碳点领域的研究进展和挑战.     

A Supramolecular Polymer Network of Graphene Quantum Dots

Graphene quantum dot (GQD)–organic hybrid compounds (GQD‐ 2 b – e ) were prepared by introducing 3,4,5‐tri(hexadecyloxy)benzyl groups (C16) and linear chains terminated with a 2‐ureido‐4‐[1H]‐pyrimidinone (UPy) moiety onto the periphery of GQD‐ 1 . GQD‐ 2 b – e formed supramolecular assemblies through hydrogen bonding between the UPy units. GPC analysis showed that GQDs with high loadings of the UPy group formed larger assemblies, and this trend was confirmed by DOSY and viscosity measurements. AFM images showed the polymeric network structures of GQD‐ 2 e on mica with flat structures (ca. 1.1 nm in height), but no such structures were observed in GQD‐ 2 a , which only carries the C16 group. GQD‐ 2 c and GQD‐ 2 d formed organogels in n‐decanol, and the gelation properties can be altered by replacing the alkyl chains in the UPy group with ethylene glycol chains (GQD‐ 3 ). GQD can thus be used as a platform for supramolecular polymers and organogelators by suitable chemical functionalization.     

氮掺杂石墨烯量子点/钯纳米复合材料的研究

铂基催化剂因具有高催化活性、高稳定性而成为极其重要的能源转化催化剂。本文采用水热法合成氮掺杂石墨烯量子点支撑的钯纳米复合材料(Pd@N-GQDs),并将其用于碱性介质中甲醇的电催化氧化反应。实验结果表明,相比同类型材料钯负载于石墨烯纳米片(Pd@GS)、钯负载于石墨烯量子点(Pd@GQDs)和商业钯黑催化剂(Pd@C),Pd@N-GQDs纳米材料具有很高的催化活性和稳定性,并可减少催化剂材料中贵金属的使用量。