Interaction of silicon-based quantum dots with gibel carp liver: oxidative and structural modifications

Quantum dots (QDs) interaction with living organisms is of central interest due to their various biological and medical applications. One of the most important mechanisms proposed for various silicon nanoparticle-mediated toxicity is oxidative stress. We investigated the basic processes of cellular damage by oxidative stress and tissue injury following QD accumulation in the gibel carp liver after intraperitoneal injection of a single dose of 2 mg/kg body weight Si/SiO₂ QDs after 1, 3, and 7 days from their administration.QDs gradual accumulation was highlighted by fluorescence microscopy, and subsequent histological changes in the hepatic tissue were noted. After 1 and 3 days, QD-treated fish showed an increased number of macrophage clusters and fibrosis, while hepatocyte basophilia and isolated hepatolytic microlesions were observed only after substantial QDs accumulation in the liver parenchyma, at 7 days after IP injection.Induction of oxidative stress in fish liver was revealed by the formation of malondialdehyde and advanced oxidation protein products, as well as a decrease in protein thiol groups and reduced glutathione levels. The liver enzymatic antioxidant defense was modulated to maintain the redox status in response to the changes initiated by Si/SiO₂ QDs. So, catalase and glutathione peroxidase activities were upregulated starting from the first day after injection, while the activity of superoxide dismutase increased only after 7 days. The oxidative damage that still occurred may impair the activity of more sensitive enzymes. A significant inhibition in glucose-6-phosphate dehydrogenase and glutathione-S-transferase activity was noted, while glutathione reductase remained unaltered.Taking into account that the reduced glutathione level had a deep decline and the level of lipid peroxidation products remained highly increased in the time interval we studied, it appears that the liver antioxidant defense of Carassius gibelio does not counteract the oxidative stress induced 7 days after silicon-based QDs exposure in an efficient manner.     

谷氨酰胺为稳定剂制备硒化镉纳米晶及光谱性质研究

以谷氨酰胺(Gln)为稳定剂合成了硒化镉纳米晶,利用X-射线粉末衍射(XRD)和透射电镜(TEM)对纳米晶结构进行了表征,粒径约为20 nm。通过紫外-可见吸收光谱、激发光谱与发射光谱研究了纳米晶光谱特性。实验结果表明,反应温度过高、反应时间过长都会破坏谷氨酰胺(Gln)的稳定作用,使CdSe聚集,影响其荧光性质。而聚乙二醇(PEG)的加入会使纳米晶的荧光发射明显加强,而且发射峰峰形尖锐。     

A study of nitrogen incorporation in pyramidal site-controlled quantum dots

We present the results of a study of nitrogen incorporation in metalorganic-vapour-phase epitaxy-grown site-controlled quantum dots (QDs). We report for the first time on a significant incorporation (approximately 0.3%), producing a noteworthy red shift (at least 50 meV) in some of our samples. Depending on the level of nitrogen incorporation/exposure, strong modifications of the optical features are found (variable distribution of the emission homogeneity, fine-structure splitting, few-particle effects). We discuss our results, especially in relation to a specific reproducible sample which has noticeable features: the usual pattern of the excitonic transitions is altered and the fine-structure splitting is suppressed to vanishing values. Distinctively, nitrogen incorporation can be achieved without detriment to the optical quality, as confirmed by narrow linewidths and photon correlation spectroscopy.     

提高钙钛矿量子点稳定性的研究进展

钙钛矿量子点具有发光谱带较窄、发光可调、量子效率高等优异的光学性能,在发光二极管、激光发射器等领域广受关注。但是钙钛矿量子点由于强离子性、高表面能及表面配体易迁移等特性而对环境高度敏感,使其在实际应用中受到限制。本文简要介绍了钙钛矿量子点结构和不稳定的原因,综述了近年来提高钙钛矿量子点稳定性的主要方法,重点从离子掺杂、表面钝化、表面包覆及多重保护4个方面展开论述。最后从绿色环保的角度出发,对高稳定生物质基钙钛矿量子点材料的制备进行了展望,提出使用具有特定结构的生物质材料及其衍生材料取代传统石油基试剂作为配体、溶剂或吸附重金属离子的外壳材料,可加速钙钛矿量子点朝着绿色低毒的方向发展。     

Improved photoluminescence quantum yield of CsPbBr3 quantum dots glass ceramics

We have fabricated CsPbBr₃ perovskite quantum dots (QDs) in a multi-component borate glass by melt-quenching technique. Transmission electron microscopy (TEM) reveals a cubic phase CsPbBr₃ crystal for QDs. As the treatment temperature or the treatment time duration increases, the photoluminescence (PL) peak shifts to long wavelength in the range of 510 to 525 nm, and the full width at half-maximum varies in the range of 24 to 18 nm. The absorption edge shifts to low energy side in the range of 2.54 to 2.41 eV. The different photoluminescence excitation spectra (PLE) reflect the change of microstructure for different samples. The PL peak wavelength and line-shape are independent of excitation wavelength. These results of spectra show typical exciton emission characteristics. As treatment conditions strengthens, photoluminescence quantum yield (PLQY) first increases and then decreases, having the best PLQY 86.9%. Bi-exponential fitting curves show that short lifetime τ₁ continuously decreases. Long lifetime τ₂, weight for long lifetime component, and average lifetime τ_avg first increase and then decrease. The PLQY values are affected by both τ₁ and τ₂, which are relative to the crystal quality in the interior and the surface of QDs, respectively. The high PLQY value corresponds to medium treatment condition, which is attributed to a balanced effect of crystal quality in interior and the surface of QDs.     

Colloidal monolayer titania quantum dots prepared by hydrothermal synthesis in supercritical water

Two-dimensional monolayer titania quantum dots (MTQDs) with ∼0.4 nm thickness and ∼2 nm lateral size are synthesized by supercritical water (SCW) treatment of titania nanotubes (TNTs). The morphology, chemical characteristics and the structure of MTQDs are studied. The formation mechanism of the MTQDs and the differences between SCW and low-temperature hydrothermal treatment are discussed. During the reaction, the high temperature, high pressure and high H⁺/OH⁻ concentration of SCW dissolved TNTs into MTQDs, and the intercalation property of the “active” water clusters formed from the broken hydrogen bonding network facilitated the detachment of the MTQDs from the TNTs. The above two reasons lead to the capture of the dissolved tiny particles, which could hardly preserved in low-temperature hydrothermal treatment. The MTQDs may be the minimum constituent unit existing in the reality of the anatase TiO₂. As a new member of the monolayer family, this new kind of 2D material may shed new light on the study of the monolayer materials.     

Long-lasting photoluminescence quantum yield of cesium lead halide perovskite-type quantum dots

Cesium lead halide perovskite(CsPbX₃,X=Cl,Br,I)quantum dots(QDs)and their partly Mn²⁺-substituted QDs(CsPb1–xMnxX3)attract considerable attention owing to their unique photoluminescence(PL)efficiencies.The two types of QDs,having different PL decay dynamics,needed to be further investigated in a form of aggregates to understand their solid-state-induced exciton dynamics in conjunction with their behaviors upon degradation to achieve practical applications of those promising QDs.However,thus far,these QDs have not been sufficiently investigated to obtain deep insights related to the long-term stability of their PL properties as aggregated solid-states.Therefore,in this study,we comparatively examined CsPbX₃-and CsPb1–xMnxX₃-type QDs stocked for>50 d under dark ambient conditions by using excitation wavelength-dependent PL quantum yield and time-resolved PL spectroscopy.These investigations were performed with powder samples in addition to solutions to determine the influence of the inter-QD interaction of the aged QD aggregates on their radiative decays.It turns out that the Mn²⁺-substituted QDs exhibited long-lasting PL quantum efficiencies,while the unsubstituted CsPbX₃-type QDs exhibited a drastic reduction of their PL efficiencies.And the obtained PL traces were clearly sensitive to the sample status.This is discussed with the possible interaction depending on the size and distance of the QD aggregates.     

Multi-scale ordering of self-assembled InAs/GaAs(001) quantum dots

Ordering phenomena related to the self-assembly of InAs quantum dots (QD) grown on GaAs(001) substrates are experimentally investigated on different length scales. On the shortest length-scale studied here, we examine the QD morphology and observe two types of QD shapes, i.e., pyramids and domes. Pyramids are elongated along the [1–10] directions and are bounded by {137} facets, while domes have a multi-facetted shape. By changing the growth rates, we are able to control the size and size homogeneity of freestanding QDs. QDs grown by using low growth rate are characterized by larger sizes and a narrower size distribution. The homogeneity of buried QDs is measured by photoluminescence spectroscopy and can be improved by low temperature overgrowth. The overgrowth induces the formation of nanostructures on the surface. The fabrication of self-assembled nanoholes, which are used as a template to induce short-range positioning of QDs, is also investigated. The growth of closely spaced QDs (QD molecules) containing 2–6 QDs per QD molecule is discussed. Finally, the long-range positioning of self-assembled QDs, which can be achieved by the growth on patterned substrates, is demonstrated. Lateral QD replication observed during growth of three-dimensional QD crystals is reported.     

CdSe量子点标记免疫球蛋白及光谱性质研究

以巯基乙酸为稳定剂合成了CdSe量子点,利用X-射线粉末衍射(XRD)和透射电镜(TEM)对量子点结构进行了表征,粒径约为5 nm。以碳二亚胺为缩合剂将量子点与免疫球蛋白共价连接,光谱实验结果表明CdSe量子点与免疫球蛋白有效结合,其荧光发射峰发生了红移,而半峰宽和发射强度没有明显变化。     

金属卤化物钙钛矿量子点的制备及其光催化应用研究进展

利用太阳能光催化技术生产清洁燃料、降解污染物及转化高附加值产品,是解决当前能源短缺和环境污染问题的有效途径。随着对金属卤化物钙钛矿的深入研究,成功开发出一系列能够制备出成分和形貌控制精确、产物均匀性好、结晶度高的钙钛矿量子点的合成方法,使钙钛矿量子点应用到光催化领域中。综述了热注入法、配体辅助再沉淀法、溶剂热法、微波辅助法等金属卤化物钙钛矿量子点的合成方法及金属卤化物钙钛矿量子点在光催化析氢、光催化还原二氧化碳、光催化合成有机物以及光催化降解有机物等方面的研究进展,最后对金属卤化物钙钛矿光催化剂的发展前景进行了展望。     

Synthesis of MDMO-PPV capped PbS quantum dots and their application to solar cells

Poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS quantum dots about 3-6 nm in diameter were synthesized with a novel method. Unlike the synthesis of oleic acid capped PbS quantum dots, the reactions were carried out in solution at room temperature, with the presence of a capping ligand species, MDMO-PPV. The quantum dots were used to fabricate bulk heterojunction solar cells with an indium tin oxide (ITO)/polyethylenedioxythiophene/polystyrenesulphonate (PEDOT: PSS)/MDMO-PPV: PbS/Al structure. Current density-voltage characterization of the devices showed that after the addition of the MDMO-PPV capped PbS quantum dots to MDMO-PPV film, the performance was dramatically improved compared with pristine MDMO-PPV solar cells.     

Understanding the atomic and electronic structures origin of defect luminescence of CdSe quantum dots in glass matrix

Well-defined density functional theory (DFT) calculations are performed as the first exploratory study for the atomic and electronic mechanism of defect mediated morphology and optical properties of Cd_nSe_n (n = 3, 10, 13, and 33) quantum dots (QDs) in inorganic amorphous matrix. The intrinsic defects of pristine CdSe QDs, and the interfacial defects between the QDs and surrounding amorphous matrix, were systematically studied. The calculated electronic structure suggested that the pristine CdSe QDs capped by the structural modifiers or non-bridging oxygen in the amorphous matrix gave rise to the structure reconstruction and paired defect states at the edge of the valence and conduction bands. The orbital analysis elucidated that the redistribution of the majority of HOMO and LUMO electron density was localized over the bonds formed by capping atoms and QDs. These changes in the electronic structures were further demonstrated by CdSe QDs embedded sodium silicate glasses. It turned out that Se atoms at QDs/glass interface were much more active than those found on the surface of organically passivated CdSe QDs. The results serve as a new paradigm in materials research to explore structural origins of defect emission from QDs and a new strategy to develop glasses containing QDs with high photoluminescence quantum efficiency.     

Electrodeposition of ZnO nanoflake-based photoanode sensitized by carbon quantum dots for photoelectrochemical water oxidation

We report a promising simple strategy for improving the performance of the photoanode for photoelectrochemical (PEC) water oxidation. Three-dimentional hierarchical ZnO nanoflake arrays with abundant porosity and small thickness on fluorine-doped tin oxide glass substrate (FTO) was prepared with electrodeposition. The ZnO nanoflake-based photoanode exhibits superior photoresponse and PEC capability. Furthermore, the ZnO photoanode sensitized by carbon quantum dots (CQDs) can further PEC performance due to the narrower bandgap of CQDs and the improved efficiency of photogenerated electrons transfer from CQDs to ZnO nanostructures. The morphology and properties of the sample were examined by scanning electron microscopy (SEM), cross-section SEM, UV–vis spectra, X-ray photoelectron spectra (XPS), FT-IR, X-ray diffractometry (XRD) and electrical measurements.     

Perovskite quantum dots growth in situ in transparent medium for short wavelength shielding

High energy ultraviolet (UV) and blue light (short wavelength) radiation is proved to be harmful to human eyes, skin, and biological genomes. However, developing effective shielding materials providing protect from short wavelength is still a great challenge. Here, Eu³⁺-doped CsPbBr₃ embedded in a transparent glass medium is proved to shield the short wavelength from 200 to 475 nm with high performance, which is prepared by a facile and efficient melting-quenching technique. The uniform distribution of the CsPbBr₃ quantum dots (QDs) growth in situ from the transparent glass matrix ensures the high transmittance (>90%) at the long wavelength (520-800 nm). In addition, the excellent short wavelength shielding ability of the Eu³⁺-doped CsPbBr₃ glass ceramics (EGC) is demonstrated even suffered with accelerated weathering tests as long as 480 hours. Moreover the cell viability of A549 cells is well preserved thanks to the completely blocked blue light by the as-obtained EGC, which unambiguously demonstrates the promising application of EGC as short wavelength shielding materials.     

Functionalized silicon quantum dots by N-vinylcarbazole: synthesis and spectroscopic properties

Silicon quantum dots (Si QDs) attract increasing interest nowadays due to their excellent optical and electronic properties. However, only a few optoelectronic organic molecules were reported as ligands of colloidal Si QDs. In this report, N-vinylcarbazole - a material widely used in the optoelectronics industry - was used for the modification of Si QDs as ligands. This hybrid nanomaterial exhibits different spectroscopic properties from either free ligands or Si QDs alone. Possible mechanisms were discussed. This type of new functional Si QDs may find application potentials in bioimaging, photovoltaic, or optoelectronic devices.     

混合溶剂中十八胺含量对CdSe量子点发光性能的影响

利用高温溶剂法,在十八胺(ODA)和十八醇(OD)混合溶剂中合成了CdSe量子点(QDs),表征了在不同反应时间和不同ODA与OD质量比条件下制备的QDs粒径和光学性质。结果表明,在混合溶剂中不仅可以制备出分散性良好、粒径均匀的QDs,而且还能获得高量子效率的产物;ODA含量变化基本不影响QDs的初始成核粒径,但对量子效率有很明显的影响,ODA含量的增加对获得高量子效率的产物有利。     

Effect of phase transition on SiO2-coated CsPbBr3/Cs4PbBr6 quantum dots: Air-stability and quantum efficiency improvement

To develop white light-emitting diodes (WLEDs) with wide color gamut for displays, compared with nitride-based phosphors and traditional core-shell quantum dots (QDs) such as CdSe, InP, CuInS₂, all-inorganic perovskite QDs CsPbX₃ (X = Cl, Br, I) were more promising luminescent materials due to tunable wavelength, narrow emission spectrum and high quantum efficiency. However, when QDs were made into solid form (powders or films), poor air-stability and drastic decrease of quantum efficiency would be observed in CsPbBr₃. These drawbacks would restrict their practical applications. To resolve these issues, in this paper, we proposed a new concept that zero-dimensional perovskite QDs powders Cs₄PbBr₆ with outstanding quantum efficiency and long lifetime up to three months could be successfully prepared via silica-coated method and crystal phase transition in low-temperature synthesis. This phenomenon of phase transition would be discussed in detail and the quantum efficiency could be improved from 31.41% to 45.87%. Moreover, green LEDs with high color purity of 92% and luminous efficiency of 88.59 lm/W could also be achieved by using this material. Therefore, our proposed perovskite QDs powders Cs₄PbBr₆ had extreme potential for displays applications.