Synthesis Of Colloidal Quantum Dots Research Articles

Intrinsic Chiroptical Activity and Excitonic Properties of Group II-VI Magic-Size Clusters.

Semiconductor magic-size clusters (MSCs), lying in the local minima of the potential landscape, are important intermediates that emerge during the synthesis of colloidal quantum dots. They have definite geometrical and electronic structures, thus serving as atomically precise building blocks for assembling supramolecular structures and devices with unprecedented functionalities. Here we report the intrinsic chiroptical activity in the magic-size cadmium and zinc chalcogenide clusters with magic numbers of 13, 33, and 34 possessing unique core-shell structures. They are responsive to circularly polarized light from the ultraviolet to visible region, with size-tunable energy gap, absorption wavelength, and excitonic characteristics. The origin of the chiroptical activity and the evolution of excitonic states with magic size are disclosed by time-dependent density functional theory calculations within a correlated electron-hole picture. This molecular-level understanding of the photophysical properties of group II-VI MSCs provides essential guidelines for utilizing them for chiral optoelectronics and photonics.

Synthesis and Single Crystal X-ray Diffraction Structure of an Indium Arsenide Nanocluster.

The discovery of magic-sized clusters as intermediates in the synthesis of colloidal quantum dots has allowed for insight into formation pathways and provided atomically precise molecular platforms for studying the structure and surface chemistry of those materials. The synthesis of monodisperse InAs quantum dots has been developed through the use of indium carboxylate and As(SiMe3)3 as precursors and documented to proceed through the formation of magic-sized intermediates. Herein, we report the synthesis, isolation, and single-crystal X-ray diffraction structure of an InAs nanocluster that is ubiquitous across reports of InAs quantum dot synthesis. The structure, In26As18(O2CR)24(PR'3)3, differs substantially from previously reported semiconductor nanocluster structures even within the III-V family. However, it can be structurally linked to III-V and II-VI cluster structures through the anion sublattice. Further analysis using variable temperature absorbance spectroscopy and support from computation deepen our understanding of the reported structure and InAs nanomaterials as a whole.

Solution-processed colloidal quantum dots for internet of things.

Colloidal quantum dots (CQDs) have been a hot research topic ever since they were successfully fabricated in 1993 via the hot injection method. The Nobel Prize in Chemistry 2023 was awarded to Moungi G. Bawendi, Louis E. Brus and Alexei I. Ekimov for the discovery and synthesis of quantum dots. The Internet of Things (IoT) has also attracted a lot of attention due to the technological advancements and digitalisation of the world. This review first aims to give the basics behind QD physics. After that, the history behind CQD synthesis and the different methods used to synthesize most widely researched CQD materials (CdSe, PbS and InP) are revisited. A brief introduction to what IoT is and how it works is also mentioned. Then, the most widely researched CQD devices that can be used for the main IoT components are reviewed, where the history, physics, the figures of merit (FoMs) and the state-of-the-art are discussed. Finally, the challenges and different methods for integrating CQDs into IoT devices are discussed, mentioning the future possibilities that await CQDs.

Arresting Ion Migration from the ETL Increases Stability in Infrared Light Detectors Based on III-V Colloidal Quantum Dots.

III-V colloidal quantum dots (CQDs) are of interest in infrared photodetection, and recent developments in CQDs synthesis and surface engineering have improved performance. Here this work investigates photodetector stability, finding that the diffusion of zinc ions from charge transport layers (CTLs) into the CQDs active layer increases trap density therein, leading to rapid and irreversible performance loss during operation. In an effort to prevent this, this work introduces organic blocking layers between the CQDs and ZnO layers; but these negatively impact device performance. The device is then, allowing to use a C60:BCP as top electron-transport layer (ETL) for good morphology and process compatibility, and selecting NiOX as the bottom hole-transport layer (HTL). The first round of NiOX -based devices show efficient light response but suffer from high leakage current and a low open-circuit voltage (Voc) due to pinholes. This work introduces poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) with NiOX NC to form a hybrid HTL, an addition that reduces pinhole formation, interfacial trap density, and bimolecular recombination, enhancing carrier harvesting. The photodetectors achieve 53% external quantum efficiency (EQE) at 970nm at 1V applied bias, and they maintain 95% of initial performance after 19 h of continuous illuminated operation. The photodetectors retain over 80% of performance after 80 days of shelf storage.

Molecular Additive-Assisted Tellurium Homogenization in ZnSeTe Quantum Dots.

The addition of aqueous hydrohalic acids (HX, X = F, Cl, Br) during the synthesis of colloidal quantum dots (QDs) is now widely employed to achieve high-quality QDs. However, this reliance on the use of aqueous solutions is incompatible with oxygen- and water-sensitive precursors such as those used in the synthesis of Te-alloyed ZnSe QDs. Herein, we show this incompatibility, leads to phase segregation into Te-rich and Te-poor regions, causing spectral broadening and luminescence peak shifting under high laser irradiation and applied electrical bias. Here we report a synthetic strategy to produce anhydrous-HF in-situ by using benzenecarbonyl fluoride (BF) as a chemical additive. Through in-situ 19 F nuclear magnetic resonance spectroscopy, we find that BF reacts with surfactants in tandem, ultimately producing intermediary F···H···trioctylamine adducts. These act as a pseudo-HF source that releases anhydrous HF. The controlled release of HF during the nucleation and growth steps homogenizes the Te distribution in the ZnSeTe lattice, leading to spectrally-stable blue-emitting QDs under increasing laser flux from ∼3 μW to ∼12mW and applied bias from 2.6 to 10V. Single-dot photoluminescence (PL) spectroscopy and analyses of the absorption, PL and transient absorption spectra together with density functional theory point to the role of anhydrous HF as a Te homogenizer. This article is protected by copyright. All rights reserved.

Controlled mixing during colloidal quantum dot synthesis: A proxy-concept based on equivalent parameters

Mixing is a key process parameter during liquid phase particle synthesis that requires special attention, in particular for scalable process and reactor development. This issue is especially pressing for advanced materials where on the one hand multifunctional properties require products of utmost quality, while on the other hand only few strategies for process design are yet developed. One material class in this context is quantum dot (QD) nanocrystals. By making use of automation and high throughout (HT) experimentation, we could recently demonstrate qualitatively the role of mixing on focusing and defocusing during QD synthesis by hot injection. In this work, we demonstrate the application of HT methodologies to investigate the effect of mixing as an important process parameter during process optimization and scale up. We performed reaction optimization by screening a multi-parameter design space using design of experiments (DoE) and machine learning (ML). We developed a so-called cold model as proxy that is based on equivalent mixing times (EMTs) derived from a competing parallel reaction system. Experimentally, we realized a fully automated approach using a HT platform for particle synthesis. The final dataset (128 experiments for model development including repeats and 29 experiments for prediction testing) was combined with DoE and complimented with machine learning. By doing so, with DoE, we could reduce the number of experiments required to develop a predictive, statistical knowledge base for EMTs at ambient conditions. Finally, we demonstrated the applicability of EMTs for two defined stirrer geometries to fine tune the widths of the particle size distribution and photoluminescence of QDs at increasing reaction volumes from 20 mL to 80 mL. This opens the door towards scalable processes for QDs at increased reaction volumes while maintaining product quality.

Ligand-induced surface reconstruction in Ag2S colloidal quantum dots for highly luminescent infrared fluorescence

Silver sulfide (Ag2S) colloidal quantum dots (CQDs) have attracted attention as potential bio-imaging materials owing to their narrow bandgap and biocompatibility; however, their low photoluminescence quantum yield (PLQY) has limited their applications. Here we introduce ligand-induced surface reconstruction strategy to dramatically improve the PLQY of Ag2S CQDs. We found that the low PLQY of Ag2S CQDs is due to the undesirable formation of a metallic Ag core during the CQD synthesis. By introducing alkyl thiols as oxidizing agents, the metallic Ag core is reoxidized that Ag vacancies in CQDs are refilled. This induces a reduced metallic Ag core and Ag-rich stoichiometry in the CQDs. The CQDs after the surface reconstruction show a 150× enhancement of photoluminescence at 1230 nm, with an absolute PLQY of 9%. This research suggests that simple ligand treatments can help improve the surface and optical properties of silver chalcogenide CQDs, including Ag2S CQDs, which may allow development of advanced optoelectronic devices.

Application of Scanning Tunneling Microscopy and Spectroscopy in the Studies of Colloidal Quantum Qots.

Colloidal quantum dots display remarkable optical and electrical characteristics with the potential for extensive applications in contemporary nanotechnology. As an ideal instrument for examining surface topography and local density of states (LDOS) at an atomic scale, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has become indispensable approaches to gain better understanding of their physical properties. This article presents a comprehensive review of the research advancements in measuring the electronic orbits and corresponding energy levels of colloidal quantum dots in various systems using STM and STS. The first three sections introduce the basic principles of colloidal quantum dots synthesis and the fundamental methodology of STM research on quantum dots. The fourth section explores the latest progress in the application of STM for colloidal quantum dot studies. Finally, a summary and prospective is presented.

Chemistry Nobel Prize Celebrates Colloidal Quantum Dots: Highly-Engineered, Spectrally Pure Light

The Chemistry Nobel Prize of this year has been awarded to Alexei Ekimov, Luis Brus, and Moungi Bawendi for their significant contributions to the discovery and synthesis of colloidal quantum dots. What initially started as a strategy to explore the physics of reduced dimensionality in matter has transitioned over the past 40 years into a commercially available technology platform, the largest of which provides red and green color sources for displays. In this overview, we will delve into this transition process and the pivotal roles played by the laureates.

Semiconductor clusters: Synthetic precursors for colloidal quantum dots

Semiconductor clusters have been implicated as reaction intermediates between molecular precursors and colloidal quantum dots (CQDs). The success of isolation of semiconductor clusters have enabled detailed investigation of the atomic information of semiconductor clusters. The identification of atomic information has emerged as an important topic because knowledge of the structure-function relationship of intermediate clusters has been helpful to reveal the synthetic mechanism of CQDs. Recently, they have been utilized as the synthetic precursors for CQDs, which was not readily achieved using conventional molecular precursors. This mini review briefly introduces the current understanding of their atomic information such as the composition, structure, and surface. We then discuss advantages, limitations, and the perspective of semiconductor clusters as a precursor for synthesis of CQDs.

Precursor Chemistry Enables the Surface Ligand Control of PbS Quantum Dots for Efficient Photovoltaics.

The surface ligand environment plays a dominant role in determining the physicochemical, optical, and electronic properties of colloidal quantum dots (CQDs). Specifically, the ligand-related electronic traps are the main reason for the carrier nonradiative recombination and the energetic losses in colloidal quantum dot solar cells (CQDSCs), which are usually solved with numerous advanced ligand exchange reactions. However, the synthesis process, as the essential initial step to control the surface ligand environment of CQDs, has lagged behind these post-synthesis ligand exchange reactions. The current PbS CQDs synthesis tactic generally uses lead oxide (PbO) as lead precursor, and thus suffers from the water byproducts issue increasing the surface-hydroxyl ligands and aggravating trap-induced recombination in the PbS CQDSCs. Herein, an organic-Pb precursor, lead (II) acetylacetonate (Pb(acac)2 ), is used instead of a PbO precursor to avoid the adverse impact of water byproducts. Consequently, the Pb(acac)2 precursor successfully optimizes the surface ligands of PbS CQDs by reducing the hydroxyl ligands and increasing the iodine ligands with trap-passivation ability. Finally, the Pb(acac)2 -based CQDSCs possess remarkably reduced trap states and suppressed nonradiative recombination, generating a certified record Voc of 0.652V and a champion power conversion efficiency (PCE) of 11.48% with long-term stability in planar heterojunction-structure CQDSCs.

Синтез и некоторые свойства коллоидных квантовых точек селенида ртути

The synthesis of colloidal quantum dots of mercury selenide using mercury oxide as a precursor is proposed. The proposed method is characterized by the use of a less toxic component in the reaction mixture - mercury oxide. The transmission electron microscopy method established an average diameter of 5–6 nm and the shape of quantum dots. A histogram of the size distribution of synthesized nanoparticles is presented. An important property of the synthesized nanoparticles is the crystal structure established by X-ray diffraction analysis. The established properties of the synthesized nanocrystals coincide with the literature data. The elemental composition of the nanoparticles was controlled by X-ray microanalysis. It is established that the chemical composition of quantum dots corresponds to the stoichiometric ratio of Hg elements : Se = 0,98 : 1,00. In addition, it follows from the X-ray that the oxygen content has been identified in silicon and carbon compounds, HgSe-based quantum dots do not contain traces of oxidation. The optical properties of quantum dots depend on the size of the nanoparticles. If the average diameter does not exceed 10 nm, mercury selenide particles are characterized by a monocrystalline structure with intraband absorption, the spectral energy distribution of which is subjected to dimensional quantization. As can be seen from the absorption spectra, the synthesized nanoparticles are characterized by absorption bands in the IR region, in the wavelength range up to 40 microns. The synthesized quantum dots do not possess luminescent properties, which, according to the literature data, is associated with a low probability of exciton formation for small nanoparticles (5–6 nm).

Ultrastable low-cost colloidal quantum dot microlasers of operative temperature up to 450\u2009K

Quantum dot microlasers, as multifunctional optical source components, are of great importance for full-color high-pixel display, miniaturized coherent lighting, and on-chip integrated photonic and electronic circuits. Since the first synthesis of colloidal quantum dots (CQD) in the 1990s, motivation to realize high-performance low-cost CQD micro-/nanolasers has been a driving force for more than three decades. However, the low packing density, inefficient coupling of CQDs with optical cavities, and the poor thermal stability of miniaturized complex systems make it challenging to achieve practical CQD micro-/nanolasers, especially to combine the continuous working ability at high temperatures and the low-cost potential with mass-produced synthesis technologies. Herein, we developed close-packed CQD-assembled microspheres and embedded them in a silica matrix through the rapid self-aggregation and solidification of CdSe/ZnS CQD. This technology addresses the core issues of photoluminescence (PL) quenching effect and low optical gain in traditional CQD laser research. High-efficiency low-threshold CQD microlasers are demonstrated together with long-playing (40 min) working stability even at 450 K under pulsed laser excitation, which is the highest operational temperature for CQD lasers. Moreover, single-mode CQD microlasers are obtained with tunable wavelengths across the entire visible spectral range. The chemosynthesis process supports the mass-produced potential of high-density integrated CQD microlasers, promoting CQD-based low-cost high-temperature microdevices.

Synthesis of Colloidal Quantum Dots with an Ultranarrow Photoluminescence Peak

Localization of exciton wavefunctions away from the inorganic–organic interface is proposed for synthesizing colloidal spheroidal quantum dots (QDs) with an ultranarrow photoluminescence (PL) peak ...

Synthesis and characterization of In1−xGaxP@ZnS alloy core-shell type colloidal quantum dots

We report synthesis of colloidal quantum dots (CQDs), indium gallium phosphide with zinc sulphide shell (In1−xGaxP@ZnS) by a hot injection method and investigate effects of In/Ga ratio on the optical properties of the obtained CQDs. The bandgap of CQDs (1.34–3.54eV) is controlled by the In/Ga ratio without the quantum confinement effect. The photoluminescence (PL) quantum yield is also dependent on the In/Ga ratio, and temperature dependent PL results show that the randomness of crystal lattice is the most influential parameter. These results show that the In1−xGaxP alloy CQDs can be useful for absorbing the whole range of visible light. In addition, this article can provide background knowledge regarding effect of core metal composition on the optical properties of produced CQDs.

Influence of photoactivation on luminescent properties of colloidal InP@ZnS quantum dots

The use of photo- and thermoactivation during the liquid-phase synthesis of colloidal quantum dots was found to yield luminescing InP@ZnS quantum dots with a luminescence quantum yield close to unity. Activation mode was found to have little or no influence on the maximal luminescent efficiency but affect particle size distribution. Compared to thermal activation, photoactivation ensures the formation of more monodispersed particles.

MgCl2 passivated ZnO electron transporting layer to improve PbS quantum dot solar cells

The unique tunable bandgaps and straightforward synthesis of colloidal quantum dots make them promising low-cost materials for photovoltaics. High-performance colloidal quantum dot solar cells rely on good-quality electron transporting layers (ETLs) to make carrier selective contacts. Despite extensive use of n-type oxides as ETLs, a detailed understanding of their surface and interface states as well as mechanisms to improve their optical properties are still under development. Here, we report a simple procedure to produce MgCl2 passivated ZnO nanoparticles ETLs that show improved device performance. The MgCl2 treated ZnO electron transporting layers boost the PbS colloidal quantum dot cell efficiency from 6.3% to 8.2%. The cell exhibits reduced defects leading to significant improvements of both FF and Jsc. This low-temperature MgCl2 treated ZnO electron transporting layer may be applied in solution processed tandem cells as a promising strategy to further increase cell efficiencies.

Recent Developments in Synthesis of Colloidal Quantum Dots

Recent Developments in Synthesis of Colloidal Quantum Dots

Advances in HgTe Colloidal Quantum Dots for Infrared Detectors

HgTe-based colloidal quantum dots (CQDs) fabricated between 10 nm and 20 nm in size readily lead to infrared cutoff wavelengths between 3 μm and 12 μm, due to their quantum confinement. In previous work, infrared photodetection using these films has been demonstrated to detect radiation out to a wavelength of 12 μm, and imaging in the mid-wave infrared region. In this work, a complete focal plane array and imager was fabricated and its performance measured for detecting radiation out to 12 μm. The photoconductive and optical properties of these HgTe CQD films are described, along with recent advancements in CQD detector technology. Anticipated improvements in the CQD synthesis and film deposition chemistries and techniques can raise the specific detectivity of these CQD films, bringing them closer to room-temperature operation.

Colloidal quantum dots for fluorescent labels of proteins

The work is devoted to the synthesis of colloidal quantum dots (QDs) and their bioconjugates with proteins. Various QDs were obtained as well with synthesis method in an organic solvent followed by hydrophilization and functionalization or synthesis in aqueous phase provides obtaining hydrophilic QDs directly. Particular attention is paid to the synthesis of QDs as fluorescent tags in the near infrared where minimum absorption occurs and the fluorescence of biological tissue and synthetic materials used in analytical systems. A method for the QDs synthesis of type fluorescent core/shell CdTeSe/CdS/CdZnS-PolyT with mixed telluride, selenide cadmium core with a high quantum yield and high resistance to photoaging. It is shown that these quantum dots may be effectively used in the immunoassay.