- Mechanistic study of precursor evolution in colloidal group II-VI semiconductor nanocrystal synthesis
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The molecular mechanism of precursor evolution in the synthesis of colloidal group II-VI semiconductor nanocrystals was studied using 1H, 13C, and 31P NMR spectroscopy and mass spectrometry. Tri-n-butylphosphine chalcogenides (TBPE; E = S, Se, Te) react with an oleic acid complex of cadmium or zinc (M-OA; M = Zn, Cd) in a noncoordinating solvent (octadecene (ODE), n-nonane-d20, or n-decane-d22), affording ME nanocrystals, tri-n-butylphosphine oxide (TBPO), and oleic acid anhydride ((OA)2O). Likewise, the reaction between trialkylphosphine selenide and cadmium n-octadecylphosphonic acid complex (Cd-ODPA) in tri-n-octylphosphine oxide (TOPO) produces CdSe nanocrystals, trialkylphosphine oxide, and anhydrides of n-octadecylphosphonic acid. The disappearance of tri-n-octylphosphine selenide in the presence of Cd-OA and Cd-ODPA can be fit to a single-exponential decay (kobs = (1.30 ± 0.08) × 10-3 s-1, Cd-ODPA, 260 °C, and kobs = (1.51 ± 0.04) × 10-3 s-1, Cd-OA, 117 °C). The reaction approaches completion at 70-80% conversion of TOPSe under anhydrous conditions and 100% conversion in the presence of added water. Activation parameters for the reaction between TBPSe and Cd-OA in n-nonane-d20 were determined from the temperature dependence of the TBPSe decay over the range of 358-400 K (ΔH? = 62.0 ± 2.8 kJ·mol-1, ΔS? = -145 ± 8 J·mol-1·K-1). A reaction mechanism is proposed where trialkylphsophine chalcogenides deoxygenate the oleic acid or phosphonic acid surfactant to generate trialkylphosphine oxide and oleic or phosphonic acid anhydride products. Results from kinetics experiments suggest that cleavage of the phosphorus chalcogenide double bond (TOP=E) proceeds by the nucleophilic attack of phosphonate or oleate on a (TOP=E)-M complex, generating the initial M-E bond.
- Liu, Haitao,Owen, Jonathan S.,Alivisatos, A. Paul
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- Inorganic-Ligand Quantum Dots Meet Inorganic-Ligand Semiconductor Nanoplatelets: A Promising Fusion to Construct All-Inorganic Assembly
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By the reaction of inorganic-ligand CdS/Cd2+ quantum dots (QDs) with inorganic-ligand CdSe/CdS/S2- nanoplatelets (NPLs), semiconductor CdS QDs were fused with CdSe/CdS NPLs to yield all-inorganic assemblies, accompanied by great photoluminescence-enhancement. These all-inorganic assemblies facilitate charge transport between each other and open up interesting prospects with electronic and optoelectronic nanodevices.
- Shi, Yunfeng,Lim, Sung Jun,Ma, Liang,Duan, Ning,Yan, Xin,Tang, Xiaole,Yang, Wenyan,Yang, Shu,Hu, Jiaxin,Smith, Andrew M.,Zhu, Xinyuan
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- Improvement of CdSe quantum dot sensitized solar cells by surface modification of Cu2S nanocrystal counter electrodes
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We report the improvement of a CdSe quantum-dot-sensitized solar cell (QDSSCs) based on surface modification of Cu2S nanoparticle counter-electrodes (CEs). In this work, we explored a low-cost, easy method to fabricate counter electrodes by direct deposition of colloidal Cu2S NCs on conducting FTO glass using drop casting or spin coating. The colloidal Cu2S NC films provide high surface area, which improves the catalytic activity for the redox couple and enhances the final photovoltaic performance. A CdSe QDSSC based on the 0.1 M EDT treated Cu2S CE/FTO shows a short-circuit current density (JSC) of 7.95 mA cm-2, a fill factor (FF) of 55.44%, and yielded a superior power conversion efficiency (η) of 2.1%, an improvement of 50% over that of the OA-capped Cu2S CE/FTO CE (1.4%). This journal is
- Park, Jeong-Hyun,Kang, Sung-Jin,Kim, Soojin,Lee, Hochun,Lee, Jong-Soo
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- N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots
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Delocalization of excitons within semiconductor quantum dots (QDs) into states at the interface of the inorganic core and organic ligand shell by so-called exciton-delocalizing ligands (EDLs) is a promising strategy to enhance coupling of QD excitons with proximate molecules, ions, or other QDs. EDLs thereby enable enhanced rates of charge carrier extraction from, and transport among, QDs and dynamic colorimetric sensing. The application of reported EDLs - which bind to the QDs through thiolates or dithiocarbamates - is however limited by the irreversibility of their binding and their low oxidation potentials, which lead to a high yield of photoluminescence-quenching hole trapping on the EDL. This article describes a new class of EDLs for QDs, 1,3-dimethyl-4,5-disubstituted imidazolylidene N-heterocyclic carbenes (NHCs), where the 4,5-substituents are Me, H, or Cl. Postsynthetic ligand exchange of native oleate capping ligands for NHCs results in a bathochromic shift of the optical band gap of CdSe QDs (R = 1.17 nm) of up to 111 meV while the colloidal stability of the QDs is maintained. This shift is reversible for the MeNHC-capped and HNHC-capped QDs upon protonation of the NHC. The magnitude of exciton delocalization induced by the NHC (after scaling for surface coverage) increases with the increasing acidity of its πsystem, which depends on the substituent in the 4,5-positions of the imidazolylidene. The NHC-capped QDs maintain photoluminescence quantum yields of up to 4.2 ± 1.8% for shifts of the optical band gap as large as 106 meV.
- Westmoreland, Dana E.,López-Arteaga, Rafael,Weiss, Emily A.
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- CdSe@CdS Dot@Platelet Nanocrystals: Controlled Epitaxy, Monoexponential Decay of Two-Dimensional Exciton, and Nonblinking Photoluminescence of Single Nanocrystal
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Wurtzite CdSe@CdS dot@platelet nanocrystals, dot-shaped CdSe nanocrystals encased within epitaxially grown CdS nanoplatelets, are controllably synthesized with nearly monodisperse size and shape distribution and outstanding photoluminescence (PL) properties. The excellent size and shape control with their lateral to thickness dimension ratio up to 3:1 is achieved by systematically studying the synthetic parameters, which results in a simple, tunable, yet reproducible epitaxy scheme. These special types of core/shell nanocrystals possess two-dimensional emission dipoles with the ab plane of the wurtzite structure. While their near-unity PL quantum yield and monoexponential PL decay dynamics are at the same level of the state-of-art CdSe/CdS core/shell nanocrystals in dot shape, CdSe@CdS dot@platelet nanocrystals possess ~2 orders of magnitude lower probability for initiating PL blinking at the single-nanocrystal level than the dot-shaped counterparts do.
- Wang, Yonghong,Pu, Chaodan,Lei, Hairui,Qin, Haiyan,Peng, Xiaogang
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- Reversible Transformations at Room Temperature among Three Types of CdTe Magic-Size Clusters
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We report the first observation of the reversible transformations that occur among three types of CdTe magic-size clusters (MSCs) in dispersion at room temperature and discuss our understanding of the transformation pathway. The reversible transformations were achieved with CdTe prenucleation stage samples, which were prepared with reactions of cadmium oleate [Cd(OA)2] and tri-n-octylphosphine telluride in 1-octadecene and were then dispersed in mixtures of toluene and a primary amine at room temperature. Three types of OA-passivated CdTe MSCs evolved, exhibiting sharp optical absorption singlets peaking at 371, 417, and 448 nm. The MSCs and their immediate precursor compounds (PCs; with no sharp optical absorption) are labeled by the MSC absorption peak wavelengths. The transformation between MSC-371 and MSC-417 has a distinct isosbestic point at ~385 nm and that between MSC-417 and MSC-448 at ~430 nm. Our findings suggest that these PC-enabled reversible transformations occur through a process of quasi-isomerization, transforming between PCs and their counterpart MSCs, combined with substitution reactions that cause transformation between the two involved PCs.
- Shen, Qiu,Luan, Chaoran,Rowell, Nelson,Zhang, Meng,Wang, Kun,Willis, Maureen,Chen, Xiaoqin,Yu, Kui
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- Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: Spectroscopic observation of facile metal-carboxylate displacement and binding
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We demonstrate that metal carboxylate complexes (L-M(O2CR) 2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N′,N′- tetramethylbutylene-1,4-diamine, pyridine, N,N,N′,N′- tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by 1H NMR spectroscopy and depends most strongly on geometric factors such as sterics and chelation, although also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L-M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface-bound Cd(O 2CR)2 from CdSe and CdS nanocrystals decreases the Cd/Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1S e-2S3/2h absorption, and decreases the photoluminescence quantum yield (PLQY) from 10% to 2CR) 2 at room temperature (~60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O 2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.
- Anderson, Nicholas C.,Hendricks, Mark P.,Choi, Joshua J.,Owen, Jonathan S.
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- Colloidal CdSe Nanoplatelets, A Model for Surface Chemistry/Optoelectronic Property Relations in Semiconductor Nanocrystals
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While the surface termination of quasi-spherical metal chalcogenide nanocrystals or quantum dots has been widely investigated, it remains unclear whether the ensuing surface chemistry models apply to similar nanocrystals with anisotropic shapes. In this work, we report on the surface-chemistry of 2D CdSe nanoplatelets, where we make use of an improved synthesis strategy that yields stable and aggregation free nanoplatelet suspensions with a photoluminescence quantum yield as high as 55%. We confirm that such nanoplatelets are enriched in Cd and, by means of 1H nuclear magnetic resonance spectroscopy, we show that the Cd-rich surface is terminated by X-type carboxylate ligands. Not unlike CdSe quantum dots (QDs), entire cadmium carboxylate entities can be displaced by the addition of amines, and the desorption isotherm points toward a considerable binding site heterogeneity. Moreover, we find that even the slightest displacement of cadmium carboxylate ligands quenches the nanoplatelet photoluminescence. These experimental findings are further confirmed by density functional theory (DFT) calculations on a 5 monolayer model CdSe nanoplatelet. These simulations show that the most labile ligands are located in the vicinity of facet edges, and that the displacement of ligands from such edge sites creates midgap states that can account for the observed photoluminescence quenching. Next to extending surface chemistry insights from colloidal QDs to nanoplatelets, this work indicates that CdSe nanoplatelets constitute a unique nanocrystal model system to establish a comprehensive description of midgap trap states, which includes their structural, chemical, and electronic properties.
- Singh, Shalini,Tomar, Renu,Ten Brinck, Stephanie,De Roo, Jonathan,Geiregat, Pieter,Martins, José C.,Infante, Ivan,Hens, Zeger
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- Synthesis and Characterization of Ni2+-Doped CdSe and CdSe(S) Quantum Dots
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The Ni-doped CdSe and CdSe(S) nanocrystals were synthesized using oleic and pelargic acids as stabilising agents and investigated by transmission electron microscopy, optical spectroscopy and inductively coupled plasma atomic emission spectroscopy.
- Dotsenko, Anna S.,Dorofeev, Sergey G.,Znamenkov, Konstantin O.,Grigoriev, Denis V.
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- Solution structure of cadmium carboxylate and its implications for the synthesis of cadmium chalcogenide nanocrystals
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Diffusion-ordered spectroscopy (DOSY) was used to investigate the solution structure of cadmium carboxylate. The molecular weights of cadmium complexes highly depend on the solvent; the complexes are polymeric in toluene but break up in the presence of polar solvents or coordinating ligands.
- Garcia-Rodriguez, Raul,Liu, Haitao
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- Sulfur copolymer for the direct synthesis of ligand-free CdS nanoparticles
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Organic coordinating ligands are ubiquitously used to solubilize, stabilize and functionalize colloidal nanoparticles. Aliphatic organic ligands are typically used to control size during the nanoparticle growth period and are used as a high boiling point solvent for solution-based synthesis procedures. However, these aliphatic ligands are typically not well suited for the end use of the nanoparticles, so additional ligand exchange or ligand stripping procedures must be implemented after the nanoparticle synthesis. Herein we present a ligand-free CdS nanoparticle synthesis procedure using a unique sulfur copolymer. The sulfur copolymer is derived from elemental sulfur, which is a cheap and abundant material. This copolymer is used as a sulfur source and high boiling point solvent, which produces stabilized metal-sulfide nanoparticles that are suspended within a sulfur copolymer matrix. The copolymer can then be removed, thereby yielding ligand-free metal-sulfide nanoparticles.
- Martin, Trevor R.,Mazzio, Katherine A.,Hillhouse, Hugh W.,Luscombe, Christine K.
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- Two-photon-induced photoenhancement of densely packed CdSe/ZnSe/ZnS nanocrystal solids and its application to multilayer optical data storage
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We report on a two-photon absorption-induced photoenhancement effect on a densely packed CdSe/ZnSe/ZnS core-shell semiconductor nanocrystal solid film. The enhancement is found to be irreversible without a noticeable blueshift in emission spectra, hence we attribute the enhancement to the photoannealing of interface defects rather than to the photo-oxidation or surface passivation by other molecules. The two-photon enhancement allows us to record the enhanced spots three dimensionally, hence demonstrating the feasibility of its application to multilayered optical data storage based on nanocrystal solids.
- Chon, James W. M.,Zijlstra, Peter,Gu, Min,Van Embden, Joel,Mulvaney, Paul
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- Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots
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We present a fully continuous chip microreactor-based multistage platform for the synthesis of quantum dots with heterostructures. The use of custom-designed chip reactors enables precise control of heating profiles and flow distribution across the microfluidic channels while conducting multistep reactions. The platform can be easily reconfigured by reconnecting the differently designed chip reactors allowing for screening of various reaction parameters during the synthesis of nanocrystals. III–V core/shell quantum dots are chosen as model reaction systems, including InP/ZnS, InP/ZnSe, InP/CdS and InAs/InP, which are prepared in flow using a maximum of six chip reactors in series.
- Baek, Jinyoung,Shen, Yi,Lignos, Ioannis,Bawendi, Moungi G.,Jensen, Klavs F.
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- Mechanistic insights into the role of alkylamine in the synthesis of CdSe nanocrystals
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This paper reports a detailed mechanistic study of the effect of alkylamine on the synthesis of CdSe nanocrystals. Alkylamines are one of the most important additives for the synthesis of colloidal semiconductor nanocrystals. However, their effect on the monomer production as well as nanocrystal nucleation and growth are not well understood, as indicted by inconsistent and contradictory conclusions in the literature. We found that alkylamines slow down the reaction between cadmium oleate and trialkyl phosphine selenide by binding to cadmium and preventing the activation of trialkyl phosphine selenide. A linear correlation was observed between the observed reaction rate constant and the 31P NMR chemical shift or 1JP-Se of phosphine selenide. In the presence of alkylamine, an alkylaminophosphonium intermediate was observed. Mechanistic study suggests that the cleavage of Pi -Se bond is through nucleophilic attack by carboxylate instead of alkylamine. Interestingly, although alkylamines decrease the rate of monomer production, it increases the rate of CdSe nanocrystal growth. Although seemingly contradictory, this is due to a drastic decrease in the nanocrystal nucleation events in the presence of alkylamines. As a result, each nucleus is fed with more monomers and grows faster in the presence of alkylamine than in its absence.
- Garcia-Rodriguez, Raul,Liu, Haitao
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- Fragmentation of Magic-Size Cluster Precursor Compounds into Ultrasmall CdS Quantum Dots with Enhanced Particle Yield at Low Temperatures
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Colloidal small-size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic-size clusters (MSC). Here, we report our synthesis of small-size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)2) and sulfur (S) in 1-octadecene (ODE), we show that after the formation of the PC in the pre-nucleation stage, the addition of tri-n-octylphosphine oxide (TOPO) facilitates the production of small-size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small-size QDs even at room temperature. Our findings introduce a new approach to making small-size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two-pathway model proposed for the pre-nucleation stage of colloidal binary QDs, the present study aids in the advance of non-classical nucleation theory.
- Chen, Xiaoqin,Fan, Hongsong,Huang, Wen,Li, Lijia,Lu, Jiao,Rowell, Nelson,Wang, Shanling,Yu, Kui,Zhang, Chunchun,Zhang, Jing,Zhang, Meng
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- Tuning emission and Stokes shift of CdS quantum dots via copper and indium co-doping
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Strongly luminescent copper and indium co-doped CdS quantum dots (CuIn-doped CdS QDs) were synthesized from copper iodide, indium acetate, cadmium oleate, and 1-dodecanethiol as starting compounds in octadecene solvent. We demonstrated that when co-doping with In, Cu ions can homogeneously dope into CdS QDs and exist in the +1 state. The as-prepared doped QDs exhibited photoluminescence (PL) in the range of 590-800 nm, with a maximum fluorescence quantum yield (QY) of 40%. They also exhibited tunable large Stokes shifts from 100 nm to 300 nm via tuning dopant concentrations of Cu and In. Such an extremely large Stokes shift dramatically decreased the self-reabsorption of QDs. Furthermore, the CuIn-doped CdS QDs exhibited excellent thermal stability and lost only approximately 20% of their emission QY when the temperature was increased from 20 °C to 150°C. These features make these QDs suitable as emitters for application in lighting. This journal is
- Liu, Mingming,Yao, Wei,Li, Cun,Wu, Zhenyu,Li, Liang
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- The formation mechanism of CdSe QDs through the thermolysis of Cd(oleate)2 and TOPSe in the presence of alkylamine
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The thermal decomposition of Cd(oleate)2, a metal organocarboxylate complex, in the presence of alkylamine was studied in order to understand the formation mechanism of CdSe nanocrystals (quantum dots, QDs) in the hot-injection method. The major intermediates and side products were characterized by nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the nucleophilic attack of the metal-coordinated amine toward the most electron-deficient carbonyl carbon of the oleate ligands initiated decomposition to generate a CdO cluster (or oligomer). Based on our experimental results, we proposed a two-step formation mechanism of CdSe QDs involving the formation of CdO intermediates with alkylamines playing a critical role as nucleophiles in the thermolysis process, followed by a metathesis reaction with trioctylphosphine selenide (TOPSe) as a chalcogenide source. This journal is the Partner Organisations 2014.
- Kim, Taekeun,Jung, Yun Ku,Lee, Jin-Kyu
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- Thiol treatment to enhance photoluminescence and electroluminescence of CdSe/CdS core-shell quantum dots prepared by thermal cycling of single source precursors
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Stable and high photoluminescence quantum-yield CdSe/CdS core-shell quantum dots (QDs) with a zinc blende (ZB) structure in both the core and the shell are prepared by over-coating CdSe core nanocrystals with a controlled number of CdS monolayers (MLs). The epitaxial growth reaction is induced via the temperature cycling of a single-source precursor, namely cadmium diethyldithiocarbamate (Cd(DEDTC)2), in oleylamine (OLA) and 1-octadecene (ODE) at temperatures between 140 and 200°C. The quantum yield of the resulting core-shell quantum dots is then enhanced by means of a ligand exchange process with alkanethiol. The ligand-protected CdSe/CdS core-shell QDs are spin coated on an indium tin oxide (ITO)-glass substrate to form a type-I QD light-emitting device (QD-LED). It is shown that the QD-LED has a current efficiency of 0.22 cd A-1. Notably, the current efficiency is 4.5 times higher than that of a QD-LED incorporating non-thiol-protected QDs, and is comparable to the best reported performance for type-I QD-LED devices in the literature.
- Chen, Chih-Jung,Chiang, Ray-Kuang,Huang, Chun-Yuan,Lien, Jiun-Yi,Wang, Sue-Lein
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- Scalable Synthesis of InAs Quantum Dots Mediated through Indium Redox Chemistry
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Next-generation optoelectronic applications centered in the near-infrared (NIR) and short-wave infrared (SWIR) wavelength regimes require high-quality materials. Among these materials, colloidal InAs quantum dots (QDs) stand out as an infrared-active candidate material for biological imaging, lighting, and sensing applications. Despite significant development of their optical properties, the synthesis of InAs QDs still routinely relies on hazardous, commercially unavailable precursors. Herein, we describe a straightforward single hot injection procedure revolving around In(I)Cl as the key precursor. Acting as a simultaneous reducing agent and In source, In(I)Cl smoothly reacts with a tris(amino)arsenic precursor to yield colloidal InAs quantitatively and at gram scale. Tuning the reaction temperature produces InAs cores with a first excitonic absorption feature in the range of 700-1400 nm. A dynamic disproportionation equilibrium between In(I), In metal, and In(III) opens up additional flexibility in precursor selection. CdSe shell growth on the produced cores enhances their optical properties, furnishing particles with center emission wavelengths between 1000 and 1500 nm and narrow photoluminescence full-width at half-maximum (FWHM) of about 120 meV throughout. The simplicity, scalability, and tunability of the disclosed precursor platform are anticipated to inspire further research on In-based colloidal QDs.
- Ginterseder, Matthias,Franke, Daniel,Perkinson, Collin F.,Wang, Lili,Hansen, Eric C.,Bawendi, Moungi G.
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- Photoluminescent Aerogels from Quantum Wells
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Highly porous self-supported three-dimensional aerogel monoliths are synthesized from strongly quantum confined quantum wells, namely, 5 monolayer thick CdSe and CdSe/CdS core/crown nanoplatelets. The aerogels are synthesized by hydrogelation of the aqueous quantum well solutions and subsequent supercritical drying. The aerogels are optically characterized by UV-vis absorption spectroscopy, emission spectroscopy, and photoluminescence (PL) decay analysis. Morphological and structural characterizations are achieved by transmission electron microscopy, scanning electron microscopy, and X-ray diffractometry. The macroscopic aerogels exhibit extremely low densities of 0.038 ± 0.007 g·cm-3 and a significantly high specific surface area of 219 m2·g-1 with nearly entirely (111) as the exposed crystal facet. Moreover, the aerogels feature properties related to quantum confinement comparable to those of their original building blocks with photoluminescence quantum yields up to 10.3%.
- Naskar, Suraj,Miethe, Jan F.,Sánchez-Paradinas, Sara,Schmidt, Nadeschda,Kanthasamy, Karthiga,Behrens, Peter,Pfnür, Herbert,Bigall, Nadja C.
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- A Selective Cation Exchange Strategy for the Synthesis of Colloidal Yb3+-Doped Chalcogenide Nanocrystals with Strong Broadband Visible Absorption and Long-Lived Near-Infrared Emission
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Doping lanthanide ions into colloidal semiconductor nanocrystals is a promising strategy for combining their sharp and efficient 4f-4f emission with the strong broadband absorption and low-phonon-energy crystalline environment of semiconductors to make new solution-processable spectral-conversion nanophosphors, but synthesis of this class of materials has proven extraordinarily challenging because of fundamental chemical incompatibilities between lanthanides and most intermediate-gap semiconductors. Here, we present a new strategy for accessing lanthanide-doped visible-light-absorbing semiconductor nanocrystals by demonstrating selective cation exchange to convert precursor Yb3+-doped NaInS2 nanocrystals into Yb3+-doped PbIn2S4 nanocrystals. Excitation spectra and time-resolved photoluminescence measurements confirm that Yb3+ is both incorporated within the PbIn2S4 nanocrystals and sensitized by visible-light photoexcitation of these nanocrystals. This combination of strong broadband visible absorption, sharp near-infrared emission, and long (>400 μs) emission lifetimes in a colloidal nanocrystal system opens promising new opportunities for both fundamental-science and next-generation spectral-conversion applications such as luminescent solar concentrators.
- Creutz, Sidney E.,Fainblat, Rachel,Kim, Younghwan,De Siena, Michael C.,Gamelin, Daniel R.
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- A convenient synthesis of cadmium chalcogenide quantum dots from cadmium acetate and bis(diphenylphosphino)methane monosulfide and -selenide or 1,4-bis(diphenylphosphino)butane monoselenide
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The synthesis of both cadmium selenide and cadmium sulfide quantum dots has been effected using a synthetic protocol that avoids the use of volatile, toxic organocadmium reagents and alkyl phosphines.
- Faller,Parr, Jonathan
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- Cation Exchange Induced Transformation of InP Magic-Sized Clusters
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Magic-sized clusters (MSCs) can provide valuable insight into the atomically precise progression of semiconductor nanocrystal transformations. We report the conversion of an InP MSC to a Cd3P2 MSC through a cation exchange mechanism and attempt to shed light on the evolution of the physical and electronic structure of the clusters during the transformation. Utilizing a combination of spectroscopic (NMR/UV-vis) and structural characterization (ICP-OES/MS/PXRD/XPS/PDF) tools, we demonstrate retention of the original InP MSC crystal lattice as Z-type ligand exchange initially occurs. Further cation exchange induces lattice relaxation and a significant structural rearrangement. These observations contrast with reports of cation exchange in InP quantum dots, indicating unique reactivity of the InP MSC.
- Stein, Jennifer L.,Steimle, Molly I.,Terban, Maxwell W.,Petrone, Alessio,Billinge, Simon J. L.,Li, Xiaosong,Cossairt, Brandi M.
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- Precursor reaction kinetics control compositional grading and size of CdSe1-: XSx nanocrystal heterostructures
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We report a method to control the composition and microstructure of CdSe1-xSx nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents (kE) spanning 1.3 × 10-5 s-1 to 2.0 × 10-1 s-1. Depending on the relative reactivity (kSe/kS), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe1-xSx alloys (kSe/kS = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed.
- Hamachi, Leslie S.,Yang, Haoran,Jen-La Plante, Ilan,Saenz, Natalie,Qian, Kevin,Campos, Michael P.,Cleveland, Gregory T.,Rreza, Iva,Oza, Aisha,Walravens, Willem,Chan, Emory M.,Hens, Zeger,Crowther, Andrew C.,Owen, Jonathan S.
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p. 6539 - 6552
(2019/07/10)
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- High-temperature growth of thick-shell CdSe/CdS core/shell nanoplatelets
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To optimize the optical properties of semiconductor nanoplatelets, simple routes to add high-quality shells are needed. We demonstrate uniform growth of CdS shells on CdSe nanoplatelets at 300 °C, overcoming limitations of previous low-temperature synthes
- Rossinelli, Aurelio A.,Riedinger, Andreas,Marqués-Gallego, Patricia,Knüsel, Philippe N.,Antolinez, Felipe V.,Norris, David J.
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supporting information
p. 9938 - 9941
(2017/09/11)
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- Flexible quantum dot light emitting diodes based on ZnO nanoparticles
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Flexible quantum dot light emitting diodes (QLEDs) have attracted extensive attention owing to the advantages of foldability and their broad application in flexible display devices. In this work, we report high performance, mechanically flexible QLEDs based on ZnO nanoparticles used as an electron transfer layer (ETL). The QLEDs have been fabricated on poly(ethylene-terephthalate) (PET) substrates utilizing a unique structure consisting of bilayered hole transport films and ZnO nanoparticles acting as an ETL to improve the device performance owing to its appropriate energy band position and high charge mobility. The QLEDs exhibited high performance, such as a lowered turn on voltage of 1.6 V and improved current and power efficiencies of 5.20 cd A-1 and 1.80 lm W-1, respectively. They presented good flexibility with a critical bending radius of 4.5 mm, suggesting the broad application potential of flexible QLEDs.
- Pan, Jiangyong,Chen, Jing,Huang, Qianqian,Khan, Qasim,Liu, Xiang,Tao, Zhi,Lei, Wei,Xu, Feng,Zhang, Zichen
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p. 82192 - 82198
(2015/10/12)
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- Elucidation of two giants: Challenges to thick-shell synthesis in CdSe/ZnSe and ZnSe/CdS Core/shell quantum dots
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Core/thick-shell giant quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. We investigate CdSe/ZnSe and ZnSe/CdS as potential new gQDs. We show theoretically and experimentally that both can exhibit partial or complete spatial separation of an excited-state electron-hole pair (i.e., type II behavior). However, we reveal that thick-shell growth is challenged by competing processes: alloying and cation exchange. We demonstrate that these can be largely avoided by choice of shelling conditions (e.g., time, temperature, and QD core identity). The resulting CdSe/ZnSe gQDs exhibit unusual single-QD properties, principally emitting from dim gray states but having high two-exciton (biexciton) emission efficiencies, whereas ZnSe/CdS gQDs show characteristic gQD blinking suppression, though only if shelling is accompanied by partial cation exchange.
- Acharya, Krishna P.,Nguyen, Hue M.,Paulite, Melissa,Piryatinski, Andrei,Zhang, Jun,Casson, Joanna L.,Xu, Hongwu,Htoon, Han,Hollingsworth, Jennifer A.
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supporting information
p. 3755 - 3758
(2015/04/14)
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- Atomistic description of thiostannate-capped CdSe nanocrystals: Retention of four-coordinate SnS4 motif and preservation of Cd-rich stoichiometry
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Colloidal semiconductor nanocrystals (NCs) are widely studied as building blocks for novel solid-state materials. Inorganic surface functionalization, used to displace native organic capping ligands from NC surfaces, has been a major enabler of electronic solid-state devices based on colloidal NCs. At the same time, very little is known about the atomistic details of the organic-to-inorganic ligand exchange and binding motifs at the NC surface, severely limiting further progress in designing all-inorganic NCs and NC solids. Taking thiostannates (K4SnS4, K4Sn2S6, K6Sn2S7) as typical examples of chalcogenidometallate ligands and oleate-capped CdSe NCs as a model NC system, in this study we address these questions through the combined application of solution 1H NMR spectroscopy, solution and solid-state 119Sn NMR spectroscopy, far-infrared and X-ray absorption spectroscopies, elemental analysis, and by DFT modeling. We show that through the X-type oleate-to-thiostannate ligand exchange, CdSe NCs retain their Cd-rich stoichiometry, with a stoichiometric CdSe core and surface Cd adatoms serving as binding sites for terminal S atoms of the thiostannates ligands, leading to all-inorganic (CdSe)core[Cdm(Sn2S7)yK(6y-2m)]shell (taking Sn2S76- ligand as an example). Thiostannates SnS44- and Sn2S76- retain (distorted) tetrahedral SnS4 geometry upon binding to NC surface. At the same time, experiments and simulations point to lower stability of Sn2S64- (and SnS32-) in most solvents and its lower adaptability to the NC surface caused by rigid Sn2S2 rings.
- Protesescu, Loredana,Nachtegaal, Maarten,Voznyy, Oleksandr,Borovinskaya, Olga,Rossini, Aaron J.,Emsley, Lyndon,Copret, Christophe,Günther, Detlef,Sargent, Edward H.,Kovalenko, Maksym V.
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p. 1862 - 1874
(2015/03/04)
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- Efficient solid-state light-emitting CuCdS nanocrystals synthesized in air
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Semiconductor nanocrystals (NCs) possess high photoluminescence (PL) typically in the solution phase. In contrary, PL rapidly quenches in the solid state. Efficient solid state luminescence can be achieved by inducing a large Stokes shift. Here we report on a novel synthesis of compositionally controlled CuCdS NCs in air avoiding the usual complexity of using inert atmosphere. These NCs show long-range color tunability over the entire visible range with a remarkable Stokes shift up to about 1.25 eV. Overcoating the NCs leads to a high solid-state PL quantum yield (QY) of ca. 55% measured by using an integrating sphere. Unique charge carrier recombination mechanisms have been recognized from the NCs, which are correlated to the internal NC structure probed by using extended X-ray absorption fine structure (EXAFS) spectroscopy. EXAFS measurements show a Cu-rich surface and Cd-rich interior with 46% CuI being randomly distributed within 84% of the NC volume creating additional transition states for PL. Color-tunable solid-state luminescence remains stable in air enabling fabrication of light-emitting diodes (LEDs).
- Khan, Ali Hossain,Dalui, Amit,Mukherjee, Soham,Segre, Carlo U.,Sarma,Acharya, Somobrata
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supporting information
p. 2643 - 2648
(2015/03/04)
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- The formation mechanism of binary semiconductor nanomaterials: Shared by single-source and dual-source precursor approaches
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One thing in common: The formation of binary colloidal semiconductor nanocrystals from single- (M(EEPPh2)n) and dual-source precursors (metal carboxylates M(OOCR)n and phosphine chalcogenides such as E=PHPh2) is found to proceed through a common mechanism. For CdSe as a model system 31Pa NMR spectroscopy and DFT calculations support a reaction mechanism which includes numerous metathesis equilibriums and Se exchange reactions. Copyright
- Yu, Kui,Liu, Xiangyang,Zeng, Qun,Yang, Mingli,Ouyang, Jianying,Wang, Xinqin,Tao, Ye
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supporting information
p. 11034 - 11039
(2013/10/22)
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