Influence of the Dielectric Environment on the Photoluminescence Intermittency of CdSe Quantum Dots

We show experimentally that the photoluminescence intermittency (blinking) of single CdSe quantum dots (QDs) is influenced by the dielectric properties of the embedding environment (matrix), the type of ligands and the capping shell. For the on‐times, we observe (and tentatively explain) a strong deviation from the commonly reported inverse power law behaviour, which can be taken into account by an exponential cut‐off at long times. We assign this component to the photoejection of the electron, while the power law behaviour is a combination of hole‐ and electron‐trapping processes. The cut‐off times and their distributions depend strongly on the polarity of the environment. Also, the off‐times show, though on a much longer timescale, deviations from the inverse power laws. We suggest a model including surface states and self‐trapped states, which quantitatively explains the experimental observations.     

Size Effect of Graphene Quantum Dots on Photoluminescence

High-photoluminescence (PL) graphene quantum dots (GQDs) were synthesized by a simple one-pot hydrothermal process, then separated by dialysis bags of different molecular weights. Four separated GQDs of varying sizes were obtained and displayed different PL intensities. With the decreasing size of separated GQDs, the intensity of the emission peak becomes much stronger. Finally, the GQDs of the smallest size revealed the most energetic PL intensity in four separated GQDs. The PL energy of all the separated GQDs shifted slightly, supported by density functional theory calculations.     

The Influence of Surface Modification on the Photoluminescence of CdTe Quantum Dots: Realization of Bio‐Imaging via Cost‐Effective Polymer

To impart biocompatibility, stability, and specificity to quantum dots (QDs)—and to reduce their toxicity—it is essential to carry out surface modification. However, most surface‐modification processes are costly, complicated, and time‐consuming. In addition, the modified QDs often have a large size, which leads to easy aggregation in biological environments, making it difficult to excrete them from in vivo systems. To solve these problems, three kinds of conventional polymers, namely, polyvinyl alcohol (PVA, neutral), sodium polystyrene sulfonate (PSS, negative charged), and poly(diallyl dimethyl ammonium chloride) (PDDA, positive charged) were selected to modify the surface of QDs at low cost via a simple process in which the size of the QDs was kept small after modification. The effect of polymer modification on the photoluminescence (PL) properties of the QDs was systematically investigated. High quantum yields (QYs) of 65 % were reached, which is important for the realization of bio‐imaging. Then, the cytotoxicity of CdTe QD–polymer composites was systematically investigated via MTT assay using the Cal27 and HeLa cell lines, especially for high concentrations of QD–polymer composites in vitro. The experimental results showed that the cytotoxicity decreased in the order CdTe‐PDDA>CdTe>CdTe‐PSS>CdTe‐PVA, indicating that PSS and PVA can reduce the toxicity of the QDs. An obvious cytotoxicity of CdTe‐PVA and CdTe‐PSS was present until 120 h for the Cal27 cell line and until 168 h for the HeLa cell line. At last, the Cal27 cell line was selected to realize bio‐imaging using CdTe‐PSS and CdTe‐PVA composites with different emission colors under one excitation wavelength.     

碳量子点的荧光发射机制

碳量子点(CQDs)一般是指粒径小于10 nm的零维碳材料,因其具有优良的光学特性而在生物成像、光学器件、生物复合材料和生物传感等领域得到广泛应用,并有望成为未来应用最广泛的一种碳材料.CQDs的光学特性受粒径、表面官能团及合成的条件(如温度、溶剂的种类和pH等)的影响,为了精准调控其光学性能以及进一步扩大其应用范围,...     

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。     

CdSe量子点的合成及标记胃蛋白酶的研究

以硒粉及镉盐为反应前体,通过固相/液相沉淀反应及室温乙二胺溶剂体系两种方法合成了平均粒径为8～10nm的CdSe量子点,以巯基乙酸修饰量子点使之可溶,并标记胃蛋白酶。CdSe量子点在350和380nm附近有明显尖锐的紫外吸收,有481.6nm的荧光带边发射,标记胃蛋白酶后,紫外吸收峰位不变而吸光度增强,荧光峰位蓝移至467.2nm,荧光强度降低。在最佳实验条件下,胃蛋白酶浓度在5～50mg/L范围内与荧光降低值之间呈线性关系;检出限(3σ)为0.36mg/L(n=10),方法已用于人体胃液胃蛋白酶的测定。     

柠檬酸稳定的水溶性CdSe和CdSe/CdS量子点的荧光特性

用柠檬酸(citrate)作为稳定剂合成了尺寸分布集中、荧光性质良好的水溶性CdSe量子点。通过调节合成温度可以调控CdSe量子点的尺寸及相应的最大荧光发射波长。当温度由20 ℃增加到95 ℃时,合成的CdSe量子点的平均尺寸由2.0 nm增加到3.2 nm,相应的荧光发射峰由500 nm红移到570 nm,展现出明显的量子尺寸效应。进一步制备了CdSe/CdS核壳量子点,其荧光量子产率比CdSe增加了5～10倍。系统地研究了S/Se物质的量的比对CdSe/CdS量子点荧光特性的影响,通过XPS证实了CdSe/CdS量子点中CdS壳层的存在。利用红外光谱和核磁共振波谱表征了柠檬酸分子中的羧基和羟基氧原子与CdSe量子点表面的Cd离子的配位作用,进而揭示了柠檬酸分子对水溶性CdSe量子点溶液的稳定作用。     

Molecularly Imprinted Polymer Coated Quantum Dots for Multiplexed Cell Targeting and Imaging

Advanced tools for cell imaging are of great interest for the detection, localization, and quantification of molecular biomarkers of cancer or infection. We describe a novel photopolymerization method to coat quantum dots (QDs) with polymer shells, in particular, molecularly imprinted polymers (MIPs), by using the visible light emitted from QDs excited by UV light. Fluorescent core–shell particles specifically recognizing glucuronic acid (GlcA) or N‐acetylneuraminic acid (NANA) were prepared. Simultaneous multiplexed labeling of human keratinocytes with green QDs conjugated with MIP‐GlcA and red QDs conjugated with MIP‐NANA was demonstrated by fluorescence imaging. The specificity of binding was verified with a non‐imprinted control polymer and by enzymatic cleavage of the terminal GlcA and NANA moieties. The coating strategy is potentially a generic method for the functionalization of QDs to address a much wider range of biocompatibility and biorecognition issues.     

Study on Interaction between Chitosan and CdS Quantum Dots via Photoluminescence Spectra

The interaction between CdS quantum dots and amino polysaccharide chitosan in aqueous solution was studied via photoluminescence (PL) spectra.The surface binding of chitosan with different molecular weight (MW) quenched the luminescence of QDs due to the elimination of radioactive anion vacancy centers.This process fits well with the Perrin model;lower MW chitosan exhibits higher quenching efficiency due to better availability to the surface.     

聚合物/量子点纳米复合材料的制备

量子点具有优异的光电性能,聚合物具有性质稳定、质轻、可加工性好等优点;将聚合物和量子点复合可综合两者的优点,同时还可使量子点的稳定性得以大幅度提高。得到的聚合物/量子点纳米复合材料应用领域广;其制备方法主要有简单易操作的直接分散法、在聚合物中原位生成量子点的原位生成法、在有量子点存在的聚合场所引发有机单体聚合的原位聚合法、层-层组装法以及在量子点表面直接修饰聚合物的表面直接修饰法。本文就这些制备方法进行了概要综述,并对各种方法的特点进行了总结。     

Monochelic Versus Telechelic Poly(Methyl Methacrylate) as a Matrix for Photoluminescent Nanocomposites with Quantum Dots

Nanocomposites based on CdSe or CdSe/ZnS quantum dots (QDs) and poly(methyl methacrylate) (PMMA) of different molecular weights and functionality were synthesized by ligand exchange of oleic acid with RAFT-based PMMA. The successful ligand exchange was confirmed by dynamic light scattering in combination with the approach “macromolecules—ghosts” and transmission electron microscopy. Comparative study of mono- and telechelics of PMMA revealed the similarities and differences in their behavior in formation of complexes with QDs and the optical properties of the corresponding nanocomposites. Telechelics exhibited higher efficiency in the complex formation and seemed to be promising candidates for the construction of devices based on QDs and polymer matrix for optical applications.     

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.     

表面活性剂对CdSe量子点荧光性能的影响

通过添加不同类型的表面活性剂在水相中制备了CdSe量子点。用透射电子显微镜(TEM)、X射线衍射(XRD)、X-射线光电子能谱(XPS)对其进行了表征,并用紫外-可见(UV-Vis)和荧光(PL)分光光度法研究了不同类型的表面活性剂对CdSe量子点吸收光谱和荧光光谱的影响。结果表明,加入长链的非离子型和阴离子型表面活性剂制备的CdSe量子点颗粒只有几个纳米,分散性好,量子点的荧光强度也有明显的增强,而加入阳离子表面活性剂制备的量子点颗粒团聚明显,其荧光出现淬灭。     

Employing Core‐Shell Quantum Dots as Triplet Sensitizers for Photon Upconversion

A new family of surface‐functionalized CdSe/ZnS core‐shell quantum dots (csQD) has been developed, which work as triplet sensitizers for triplet‐triplet annihilation‐based photon upconversion (TTA‐UC). The surface modification of csQD with acceptor molecules plays a key role in the efficient relay of the excited energy of csQD to emitter molecules in the bulk solution, where the generated emitter triplets undergo triplet‐triplet annihilation that leads to photon upconversion. Interestingly, improved UC properties were achieved with the core‐shell QDs compared with core‐only CdSe QDs (cQD). The threshold excitation intensity, which is defined as the necessary irradiance to achieve efficient TTA process, decreases by more than a factor of four. Furthermore, the total UC quantum yield is enhanced more than 50‐fold. These enhancements should be derived from better optical properties of csQD, in which the non‐radiative surface recombination sites are passivated by the shell layer with wider bandgap.     

CdSe量子点荧光增敏法测定甘草酸

以巯基乙酸为稳定剂水相法一步合成了CdSe量子点,并以此量子点为荧光探针,基于甘草酸(GL)对量子点的荧光增强效应,建立了一种简便、快速、灵敏测定GL的分析方法,同时对GL与CdSe量子点的反应机理进行了初步探讨.考察了多种因素对GL测定的影响.结果表明,在pH 7.4的Na2 HPO4 - NaH2 PO4缓冲溶液中...     

量子点的聚合物表面修饰及其应用

量子点作为新型纳米发光材料备受关注,但由于光学稳定性和生物相容性的问题而在实际应用上受限。聚合物对量子点的修饰能够提供量子点合成的有效支撑基质,而且还可以改善量子点的稳定性和单分散性,进而可以拓展量子点应用于化学、物理以及生物学领域。基于聚合物修饰量子点的优势,本文简述了聚合物表面修饰量子点的方法、合成路线、步骤、特点以及发展现状。其中,双亲分子涂敷的量子点可以改善量子点的水溶性;多基配体包裹的量子点更具有稳定性和功能性;末端功能化聚合物表面修饰的量子点则可以合成更为先进功能的材料;胶封树枝状定域量子点具有单分散和优越发光特性。同时,还综述了各种表面修饰方法的最新研究进展,存在问题以及应用发展趋势。     

Photoluminescence Quenching in Self‐Assembled CsPbBr3 Quantum Dots on Few‐Layer Black Phosphorus Sheets

An ordered self‐assembly of CsPbBr₃ quantum dots (QDs) was generated on the surface of few‐layer black phosphorus (FLBP). Strong quenching of the QD fluorescence was observed, and analyzed by time‐resolved photoluminescence (TR‐PL) studies, DFT calculations, and photoconductivity measurements. Charge transfer by type I band alignment is suggested to be the cause of the observed effects.     

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD–organic hybrid materials. Three peripherally functionalised GQDs having a third‐generation dendritic wedge (GQD‐ 2 ), long alkyl chains (GQD‐ 3 ) and a polyhedral oligomeric silsesquioxane group (GQD‐ 4 ) were prepared by the Cu^I‐catalysed Huisgen cycloaddition reaction of GQD‐ 1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD‐ 1 – 4 and on the five‐membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO–LUMO bandgaps of GQD‐ 1 – 4 were estimated to be approximately 2 eV, and their low‐lying LUMO levels (<?3.9 eV) were lower than that of phenyl‐C₆₁‐butyric acid methyl ester, an n‐type organic semiconductor. The solubility of GQD‐ 1 – 4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD‐ 2 , both GQD‐ 3 and GQD‐ 4 emitted white light upon excitation at 360 nm. Size‐exclusion chromatography demonstrated that white‐light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.