Controllable modulation of precursor reactivity using chemical additives for systematic synthesis of high-quality quantum dots

AbstractThe optical and electronic performance of quantum dots (QDs) are affected by their size distribution and structural quality. Although the synthetic strategies for size control are well established and widely applicable to various QD systems, the structural characteristics of QDs, such as morphology and crystallinity, are tuned mostly by trial and error in a material-specific manner. Here, we show that reaction temperature and precursor reactivity, the two parameters governing the surface-reaction kinetics during growth, govern the structural quality of QDs. For conventional precursors, their reactivity is determined by their chemical structure. Therefore, a variation of precursor reactivity requires the synthesis of different precursor molecules. As a result, existing precursor selections often have significant gaps in reactivity or require synthesis of precursor libraries comprising a large number of variants. We designed a sulfur precursor employing a boron-sulfur bond, which enables controllable modulation of their reactivity using commercially available Lewis bases. This precursor chemistry allows systematic optimization of the reaction temperature and precursor reactivity using a single precursor and grows high-quality QDs from cores of various sizes and materials. This work provides critical insights into the nanoparticle growth process and precursor designs, enabling the systematic preparation of high-quality QD of any sizes and materials.

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Size-Controlled Microwave-Assisted Synthesis of Water-Dispersible Cd(Se,S) Quantum Dots for Potential Biological Applications

MRS Proceedings ◽

10.1557/opl.2015.623 ◽

2015 ◽

Vol 1784 ◽

Cited By ~ 1

Author(s):

E. Calderón-Ortiz ◽

S. Bailón-Ruiz ◽

L. Alamo-Nole ◽

J. Rodriguez-Orengo ◽

O. Perales-Perez

Keyword(s):

Quantum Dots ◽

Optical Properties ◽

Reaction Time ◽

Reaction Temperature ◽

Quantum Confinement Effect ◽

Reactive Oxygen Species Generation ◽

Size Control ◽

Average Crystallite Size ◽

Microwave Assisted Synthesis ◽

Microwave Assisted

ABSTRACTNanomedicine is fostering significant advances in the development of platforms for early detection and treatment of diseases. Nanoparticles (NPs) like quantum dots (QDs) exhibit size-dependent optical properties for light-driven technologies, which might become important in bio-imaging, sensing and photo-dynamic therapy (PDT) applications. The present research addresses the synthesis of water-stable Cd-based QDs via a Microwave-Assisted synthesis approach using cadmium sulfate salt, and thioglycolic acid as Cd- and S-precursors, respectively. Selenide ions were available by reductive leaching of metallic Selenium in Sodium bisulfite solution. The size control and the tunability of the optical properties were achieved by a suitable control of the reaction temperature (in the 140°C- 190°C range) and reaction time (10 minutes-40 minutes). X-ray diffraction analyses suggested the development of a CdSe,S face cubic centered structure; the broadening of the diffraction peaks indicated the presence of very small nanocrystals in the samples. The average crystallite size was estimated at 5.50 nm ± 1.17nm and 3.72 nm ± 0.04 nm, for nanoparticles synthesized at 180°C after 40 minutes or 10 minutes of reaction, respectively. HRTEM images confirmed the crystalline nature and the small size of the synthesized nanocrystals. In turn, the exciton was red-shifted from 461nm to 549 nm when the reaction temperature was prolonged from 140°C to 190 °C, suggesting the crystal growth. The corresponding band gap values were approximately 2.2 eV, confirming the quantum confinement effect (bulk value 1.74eV). This red shift was also evidenced in PL measurements where the main emission peak was shifted from 507 nm to 564 nm when the samples were excited at 420 nm. A narrow size-tunable emission also was supported by the full width at half maximum (∼ 45 nm) for the synthesized nanocrystals. The reactive oxygen species generation capability of as-synthesized QDs was also investigated. The correlation between the particle size and the generation of (ROS) by the degradation of methylene blue was evident with a reduction of MB concentration from 10μM to 7.5μM and 6.7μM after 15 minutes of UV irradiation for reaction time of 10 min. and 40 min. respectively. No additional degradation was noticed after 60 minutes of irradiation.

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Profiles of teacher–child interaction quality in groups of 3-year-old children in Quebec and France

SN Social Sciences ◽

10.1007/s43545-021-00266-8 ◽

2021 ◽

Vol 1 (11) ◽

Author(s):

Maude Roy-Vallières ◽

Nathalie Bigras ◽

Annie Charron ◽

Caroline Bouchard ◽

Andréanne Gagné ◽

...

Keyword(s):

Group Size ◽

Structural Characteristics ◽

Secondary Analysis ◽

Adult Child ◽

Structural Quality ◽

High Quality ◽

Interaction Quality ◽

Child Interaction ◽

Quality Profile ◽

Medium Quality

AbstractTheory and studies support that educational quality may differ according to socio-political context even in states with similar cultures. Based on a secondary analysis of data, this study aims at identifying latent profiles of adult–child interaction quality in groups of three-year-old children in Quebec’s (Canada) early childhood centers and France’s kindergarten classrooms using the CLASS Pre-K. This study also aims to explore existing associations between identified profiles, socio-political contexts, and structural characteristics (staff qualifications, ages, group size). Latent profile analyses showed four interaction quality profiles, namely a high-quality profile (HQ), a medium–high-quality profile (MHQ), a medium quality profile (MQ), and a medium–low-quality profile (MLQ). The scores of the three CLASS Pre-K domains associated with identified profiles show a higher average interaction quality in Quebec compared with France, suggesting a more favorable sociocultural context for interaction quality in Quebec. As for characteristics of structural quality, analyses suggest that the group size variable is significantly associated with scores of interaction quality, with the HQ and the MHQ profiles showing a significantly lower group size than the MQ and MLQ profiles. Age is also significantly associated with profiles, exhibiting a general trend of younger participants found in higher quality profiles. Courses of action to enhance French policies are discussed.

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Supramolecular Assembly of U(IV) Clusters and Superatoms

10.26434/chemrxiv.11860065 ◽

2020 ◽

Author(s):

Ian Colliard ◽

Gregory Morrosin ◽

Hans-Conrad zur Loye ◽

May Nyman

Keyword(s):

Quantum Dots ◽

Supramolecular Assembly ◽

Emergent Properties ◽

Organic Media ◽

Body Centered Cubic ◽

Cluster Anions ◽

Charge Balance ◽

Interpenetrating Networks ◽

Hierarchical Assembly ◽

Two Parameters

Superatoms are nanometer-sized molecules or particles that can form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in superlattices of quantum-dots, p-block clusters, and fullerenes. Here, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters; acidity and the countercation. In acid, larger LnIII (Ln=La-Ho) link hexamer (U6) oxoclusters into body-centered cubic frameworks, while smaller LnIII (Ln=Er-Lu &Y) promote linking of fourteen U6-clusters into hollow superclusters (U84 superatoms). U84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations, and U6-clusters. Divalent transition metals (TM=MnII and ZnII), with no added acid, charge-balance and promote the fusion of 10 U6 and 10 U-monomers into a wheel–shaped cluster (U70). Dissolution of U70 in organic media reveals (by small-angle Xray scattering) that differing supramolecular assemblies are accessed, controlled by TM-linking of U70-clusters.

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High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

10.26434/chemrxiv.8335262 ◽

2019 ◽

Author(s):

Aurelio A. Rossinelli ◽

Henar Rojo ◽

Aniket S. Mule ◽

Marianne Aellen ◽

Ario Cocina ◽

...

Keyword(s):

Quantum Dots ◽

High Temperature ◽

Equilibrium Shape ◽

Size Variation ◽

Crystal Defects ◽

Atomic Scale ◽

Quantum Yields ◽

Core Shell ◽

Compositional Gradient ◽

High Quality

<div>Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, which are well known to improve the performance of quantum dots. </div><div>Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/CdxZn1–xS, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/CdxZn1–xS) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.</div>

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One-step synthesis of high-quality vanadium disulfide quantum dots for long-term lysosome-targetable imaging

Sensors and Actuators B Chemical ◽

10.1016/j.snb.2021.130544 ◽

2021 ◽

pp. 130544

Author(s):

Dan Yang ◽

Liwen Chen ◽

Le Wang ◽

Zhongjie Cui ◽

Zhuoqi Wen ◽

...

Keyword(s):

Quantum Dots ◽

High Quality ◽

One Step

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Red Light-Emitting Diodes with All-Inorganic CsPbI3/TOPO Composite Nanowires Color Conversion Films

Nanoscale Research Letters ◽

10.1186/s11671-020-03430-w ◽

2020 ◽

Vol 15 (1) ◽

Author(s):

Lung-Chien Chen ◽

Yi-Tsung Chang ◽

Ching-Ho Tien ◽

Yu-Chun Yeh ◽

Zong-Liang Tseng ◽

...

Keyword(s):

Quantum Dots ◽

Light Emitting Diode ◽

Red Light ◽

Trioctylphosphine Oxide ◽

Optical And Electrical Properties ◽

Colloidal Solutions ◽

High Quality ◽

Light Emitting ◽

Hot Injection ◽

Color Conversion

AbstractThis work presents a method for obtaining a color-converted red light source through a combination of a blue GaN light-emitting diode and a red fluorescent color conversion film of a perovskite CsPbI3/TOPO composite. High-quality CsPbI3 quantum dots (QDs) were prepared using the hot-injection method. The colloidal QD solutions were mixed with different ratios of trioctylphosphine oxide (TOPO) to form nanowires. The color conversion films prepared by the mixed ultraviolet resin and colloidal solutions were coated on blue LEDs. The optical and electrical properties of the devices were measured and analyzed at an injection current of 50 mA; it was observed that the strongest red light intensity was 93.1 cd/m2 and the external quantum efficiency was 5.7% at a wavelength of approximately 708 nm when CsPbI3/TOPO was 1:0.35.

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Highly luminescent InP-In(Zn)P/ZnSe/ZnS core/shell/shell colloidal quantum dots with tunable emission synthesized based on growth-doping

Journal of Materials Chemistry C ◽

10.1039/d1tc01664d ◽

2021 ◽

Author(s):

Cong Shen ◽

Yan Qing Zhu ◽

Zixiao Li ◽

Jingling Li ◽

Hong Tao ◽

...

Keyword(s):

Quantum Dots ◽

Near Infrared ◽

Infrared Region ◽

Colloidal Quantum Dots ◽

High Quality ◽

Promising Alternative ◽

Lower Toxicity ◽

Near Infrared Region ◽

Inp Quantum Dots ◽

Tunable Emission

InP quantum dots (QDs) are considered as the most promising alternative to Cd-based QDs with the lower toxicity and emission spectrum tunability ranging from visible to near-infrared region. Although high-quality...

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