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Quantum dot

Li Chen, Wei-Lin Chen, Jian-Ping Li, Jia-Bo Wang, En-Bo Wang
The serious electron recombination occurring in TiO2/quantum dot sensitizer/electrolyte interface is the key reason for hindering the further efficiency improvement of QDSCs. Polyoxometalate(POM) can be as electron transfer media to decreasing electron recombination of photoelectric device, which is due to the excellent oxidation reduction properties and thermostability. So in this paper, POM/TiO2 electronic interface layer prepared by a simple layer-by-layer self-assembly method is added between FTO and mesoporous TiO2 in the photoanode of the QDSCs, and their effects on the photovoltaic performance are systematically investigated...
May 23, 2017: ChemSusChem
Chongyang Zhu, Yuan Huang, Feng Xu, Peng Gao, Binghui Ge, Jing Chen, Haibo Zeng, Eli Sutter, Peter Sutter, Litao Sun
A high density of edge sites and other defects can significantly improve the catalytic activity of layered 2D materials. Herein, this study demonstrates a novel top-down strategy to maximize catalytic edge sites of MoSe2 by breaking up bulk MoSe2 into quantum dots (QDs) via "turbulent shear mixing" (TSM). The ultrasmall size of the MoSe2 QDs provides a high fraction of atoms in reactive edge sites, thus significantly improving the catalytic activities. The violent TSM further introduces abundant defects as additional active sites for electrocatalytic reactions...
May 24, 2017: Small
Zhichun Li, Long Kong, Shouqiang Huang, Liang Li
We successfully prepared QDs-silica/alumina monolith (QDs-SAM) by a simple sol-gel reaction of Al-Si single precursors with CsPbBr3 QDs blended in toluene solution, without adding water and catalyst. The resultant transparent monolith exhibits high photoluminescence quantum yields (PLQY) up to 90%, and good photostability under strong illumination of blue light for 300 h. We demonstrated that the preliminary ligand exchange of didodecyl dimethyl ammonium bromide (DDAB) was very important to protect CsPbBr3 QDs from the surface damages during sol-gel reaction, which not only allowed us to maintain the original optical properties of CsPbBr3 QDs but also avoided the aggregation of QDs and make the monolith transparent...
May 24, 2017: Angewandte Chemie
Feng Liang, Yuan Liu, Yun Hu, YingLi Shi, Yuqiang Liu, Zhao-Kui Wang, Xuedong Wang, Baoquan Sun, Liang-Sheng Liao
A facile but effective method is proposed to improve the performance of quantum dot light-emitting diodes (QLEDs) by incorporating a polymer, poly (9-vinlycarbazole) (PVK), as an additive into the CdSe/CdS/ZnS quantum dots (QDs) emitting layer (EML). It is found that the charge balance of the device with the PVK-added EML was greatly improved. In addition, the film morphology of the hole-transporting layer (HTL) which is adjacent to the EML is substantially improved. The surface roughness of the HTL is reduced from 5...
May 25, 2017: ACS Applied Materials & Interfaces
Ruixuan Yu, Tamaki Shibayama, Junya Ishioka, Xuan Meng, Yanhua Lei, Seiichi Watanabe
The in-situ observation of Au dot formation and the self-assembly dynamics of Au nanoparticles (NPs) was successfully demonstrated via dewetting of Au thin films on SiO<sub>2</sub> glass substrates under nano-second pulsed laser irradiation using a multi-quantum beam high-voltage electron microscope. Moreover, using electron energy-loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM), the plasmonic properties of the formed Au/SiO<sub>2</sub> nanostructure were analyzed to demonstrate its validity in advanced optical devices...
May 25, 2017: Nanotechnology
Jie Chen, Ji-Shi Wei, Peng Zhang, Xiao-Qing Niu, Wei Zhao, Ze-Yang Zhu, Hui Ding, Huan-Ming Xiong
Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots...
May 24, 2017: ACS Applied Materials & Interfaces
Javier Amaya Suárez, Jose J Plata, Antonio M Márquez, Javier Fdez Sanz
Quantum dot-sensitized solar cells, QDSCs, are a clean and effective alternative to fossil fuels to reduce CO2 emissions. However, the different components that constitute the QDSCs and the difficulty of isolating experimentally their effects on the performance of the whole system slow down the development of more efficient devices. In this work, DFT calculations are combined with a bottom-up approach to differentiate the effect of each component on the electronic structure and absorption spectra. First, Cu2S QDs were built including a U parameter to effectively describe the localization of electrons...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
Mathijs de Jong, Andries Meijerink, Freddy T Rabouw
In optical materials energy is usually extracted only from the lowest excited state, resulting in fundamental energy-efficiency limits such as the Shockley-Queisser limit for single-junction solar cells. Photon-cutting materials provide a way around such limits by absorbing high-energy photons and 'cutting' them into multiple low-energy excitations that can subsequently be extracted. The occurrence of photon cutting or quantum cutting has been demonstrated in a variety of materials, including semiconductor quantum dots, lanthanides and organic dyes...
May 24, 2017: Nature Communications
Pallavi Singhal, Bal Govind Vats, Sanjay Kumar Jha, Suman Neogy
Considering the high toxicity and widespread availability of fluoride ion in different environmental matrices, it is imperative to design a probe for its detection. In view of this a selective fluorescent on-off-on probe based on carbon quantum dots (CQDs) and Eu3+ has been designed. We have synthesized water soluble carboxylic acid functionalized CQDs and monitored its interaction with Eu3+. On addition of Eu3+ ions luminescence quenching in CQDs emission was observed (switch-off). We investigate the reason for this luminescence quenching using time resolved emission and high resolution transmission electron microscopy (HRTEM) studies and observed that both electron transfer from CQDs to Eu3+ and aggregation of CQDs are responsible for luminescence quenching...
May 24, 2017: ACS Applied Materials & Interfaces
Celia Ruiz-Palomero, Sandra Benítez-Martínez, M Laura Soriano, Miguel Valcárcel
A novel low-cost fluorimetric platform based on sulfur, nitrogen-codoped graphene quantum dots immersed into nanocellulosic hydrogels is designed and applied in detecting the laccase enzyme. Although most of methods for detecting laccase are based on their catalytic activity, which is strongly dependent on environmental parameters, we report a sensitive and selective method based on the fluorescence response of hydrogels containing graphene quantum dots (GQDs) acting as luminophore towards laccase. The easily-prepared gel matrix not only improves the fluorescence signal of GQDs by avoiding their self-quenching but also stabilizes their fluorescence signal and improves their sensitivity towards laccase...
June 29, 2017: Analytica Chimica Acta
Natalia Razgoniaeva, Pavel Moroz, Mingrui Yang, Darya S Budkina, Holly Eckard, Marissa Augspurger, Dmitriy Khon, Alexander N Tarnovsky, Mikhail Zamkov
The emerging generation of quantum dot optoelectronic devices offers an appealing prospect of a size-tunable band gap. The confinement-enabled control over electronic properties, however, requires nanoparticles to be sufficiently small, which leads to a large area of inter-particle boundaries in a film. Such interfaces lead to a high density of surface traps which ultimately increase the electrical resistance of a solid. To address this issue, we have developed an inverse energy-gradient core/shell architecture supporting the quantum confinement in nanoparticles larger than the exciton Bohr radius...
May 23, 2017: Journal of the American Chemical Society
Tae-Ho Kim, Chang-Seok Lee, Sangwon Kim, Jaehyun Hur, Sangmin Lee, Keun Wook Shin, Young-Zoon Yoon, Moon Kee Choi, Jiwoong Yang, Dae-Hyeong Kim, Taeghwan Hyeon, Seongjun Park, Sungwoo Hwang
Flexible and stretchable optoelectronic devices can be potentially applied in displays, biosensors, biomedicine, robotics, and energy generation. The use of nanomaterials with superior optical properties such as quantum dots (QDs) is important in the realization of wearable displays and biomedical devices, but specific structural design as well as selection of materials should preferentially accompany this technology to realize stretchable forms of these devices. Here, we report stretchable optoelectronic sensors manufactured using colloidal QDs and integrated with elastomeric substrates, whose optoelectronic properties are stable under various deformations...
May 23, 2017: ACS Nano
Kseniia Boriachek, Md Nazmul Islam, Vinod Gopalan, Alfred K Lam, Nam-Trung Nguyen, Muhammad J A Shiddiky
Tumor-derived exosomes have emerged as promising cancer biomarkers due to their unique composition and functions. Herein, we report a stripping voltammetric immunoassay for the electrochemical detection of disease-specific exosomes using quantum dots as signal amplifiers. The assay involves three subsequent steps where bulk exosome populations are initially magnetically captured on magnetic beads by a generic tetraspanin antibody (e.g., CD9 or CD63) followed by the identification of disease-specific exosomes using cancer-related...
May 23, 2017: Analyst
Laxman Tatikondewar, Anjali Kshirsagar
To investigate energy gap bowing in homogeneously alloyed CdSxSe1-x quantum dots (QDs) and to understand whether it is different from bulk, we perform density functional theory based electronic structure calculations for spherical QDs of different compositions x (0 ≤ x ≤ 1) and of varying sizes (2.2 to 4.6 nm). We find the bowing constant to be slightly higher than in bulk for different sizes of quantum dots. The change in the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of QDs mainly arises due to the change in the LUMO energies...
May 23, 2017: Physical Chemistry Chemical Physics: PCCP
Ghader Hosseinzadeh, Ali Maghari, Seyed Morteza Famil Farniya, Amir Homayoun Keihan, Ali A Moosavi-Movahedi
Interaction of quantum dots (QDs) and proteins strongly influenced by the surface characteristics of the QDs at the protein-QD interface. For a precise control of these surface-related interactions, it is necessary to improve our understanding in this field. In this regard, in the present work, the interaction between the insulin and differently functionalized ZnS quantum dots (QDs) were studied. The ZnS QDs were functionalized with various functional groups of hydroxyl (OH), carboxyl (COOH), amine (NH2), and amino acid (COOH and NH2)...
August 1, 2017: Materials Science & Engineering. C, Materials for Biological Applications
Junjian Li, Gancheng Zuo, Xiaoliang Qi, Wei Wei, Xiaohao Pan, Ting Su, Jianfa Zhang, Wei Dong
We report that nitrogen doped carbon dots (N-CDs) represent a viable fluorescent probe for the determination of Ag(+). The N-CDs can be fairly easily prepared by a hydrothermal treatment method using Salecan and dicyandiamide as the precursors, display excitation/emission maxima of 350/438nm. The N-CDs have an average diameter of about 3.8nm. The N-CDs exhibited blue fluorescence (quantum yield of 13.2%) and could response to Ag(+) selectively and sensitively. Other ions nearly had no interference. The probe has excellent selectivity, high sensitivity, and a linear response range that extends from 0 to 40μM...
August 1, 2017: Materials Science & Engineering. C, Materials for Biological Applications
Xu Zhang, Yamin Wang, Yanbao Zhao, Lei Sun
In this work, pH-sensitive "dual-switch" porous silica (pSiO2) nanoparticles (NPs) were constructed for drug delivery. Poly(acrylic acid) (PAA) was grafting onto the internal and external surfaces of amino groups functionalized porous silica (pSiO2-NH2) NPs by the amidation between the amino groups and the carboxyl groups of PAA for pH triggered drug release. The resultant pSiO2/PAA NPs have an average diameter of 50-60nm and high specific surface area (914m(2)·g(-1)). To improve the loading capacity, ZnO quantum dots (QDs) were used to block the partial pores of pSiO2/PAA and the loading capacity reached to 28% for methotrexate (MTX) model drug...
August 1, 2017: Materials Science & Engineering. C, Materials for Biological Applications
Kevin Whitham, Tobias Hanrath
The formation of epitaxially connected quantum dot solids involves a complex interplay of interfacial assembly, surface chemistry, and irreversible directed attachment. We describe the basic mechanism in context of a coherent phase transition with distinct nucleation and propagation steps. The proposed mechanism explains how defects in the pre-assembled structure influence nucleation and how basic geometric relationships govern the transformation from hexagonal assemblies of isolated dots to interconnected solids with square symmetry...
May 22, 2017: Journal of Physical Chemistry Letters
Jiaqi Guo, Dongfei Liu, Ilari Filpponen, Leena-Sisko Johansson, Jani-Markus Malho, Sakeena Quraishi, Falk Liebner, Hélder A Santos, Orlando J Rojas
We present an approach to construct biocompatible and photoluminescent hybrid materials comprised of carbon quantum dots (CQD) and TEMPO-oxidized cellulose nanocrystals (TO-CNC). First, the amino-functionalized carbon quantum dots (NH2-CQD) were synthesized using a simple microwave method and the TO-CNCs were prepared by hydrochloric acid (HCl) hydrolysis followed by TEMPO-mediated oxidation. The conjugation of NH2-CQD and TO-CNC was conducted via carbodiimide-assisted coupling chemistry. The synthesized TO-CNC@CQD hybrid nanomaterials were characterized using X-ray photoelectron spectroscopy, cryo-transmittance electron microscopy, confocal microscopy and fluorescence spectroscopy...
May 22, 2017: Biomacromolecules
Artur Branny, Santosh Kumar, Raphaël Proux, Brian D Gerardot
An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor...
May 22, 2017: Nature Communications
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