10468-30-1Relevant articles and documents
Mechanistic study of precursor evolution in colloidal group II-VI semiconductor nanocrystal synthesis
Liu, Haitao,Owen, Jonathan S.,Alivisatos, A. Paul
, p. 305 - 312 (2007)
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.
Inorganic-Ligand Quantum Dots Meet Inorganic-Ligand Semiconductor Nanoplatelets: A Promising Fusion to Construct All-Inorganic Assembly
Shi, Yunfeng,Lim, Sung Jun,Ma, Liang,Duan, Ning,Yan, Xin,Tang, Xiaole,Yang, Wenyan,Yang, Shu,Hu, Jiaxin,Smith, Andrew M.,Zhu, Xinyuan
, p. 6994 - 6998 (2021)
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.
Improvement of CdSe quantum dot sensitized solar cells by surface modification of Cu2S nanocrystal counter electrodes
Park, Jeong-Hyun,Kang, Sung-Jin,Kim, Soojin,Lee, Hochun,Lee, Jong-Soo
, p. 51471 - 51476 (2014)
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
N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots
Westmoreland, Dana E.,López-Arteaga, Rafael,Weiss, Emily A.
, p. 2690 - 2696 (2020)
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.
CdSe@CdS Dot@Platelet Nanocrystals: Controlled Epitaxy, Monoexponential Decay of Two-Dimensional Exciton, and Nonblinking Photoluminescence of Single Nanocrystal
Wang, Yonghong,Pu, Chaodan,Lei, Hairui,Qin, Haiyan,Peng, Xiaogang
, p. 17617 - 17628 (2019)
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.
Reversible Transformations at Room Temperature among Three Types of CdTe Magic-Size Clusters
Shen, Qiu,Luan, Chaoran,Rowell, Nelson,Zhang, Meng,Wang, Kun,Willis, Maureen,Chen, Xiaoqin,Yu, Kui
, p. 4243 - 4251 (2021)
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.
Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: Spectroscopic observation of facile metal-carboxylate displacement and binding
Anderson, Nicholas C.,Hendricks, Mark P.,Choi, Joshua J.,Owen, Jonathan S.
, p. 18536 - 18548 (2013)
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.
Colloidal CdSe Nanoplatelets, A Model for Surface Chemistry/Optoelectronic Property Relations in Semiconductor Nanocrystals
Singh, Shalini,Tomar, Renu,Ten Brinck, Stephanie,De Roo, Jonathan,Geiregat, Pieter,Martins, José C.,Infante, Ivan,Hens, Zeger
, p. 13292 - 13300 (2018)
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.
Synthesis and Characterization of Ni2+-Doped CdSe and CdSe(S) Quantum Dots
Dotsenko, Anna S.,Dorofeev, Sergey G.,Znamenkov, Konstantin O.,Grigoriev, Denis V.
, p. 292 - 293 (2012)
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.
Solution structure of cadmium carboxylate and its implications for the synthesis of cadmium chalcogenide nanocrystals
Garcia-Rodriguez, Raul,Liu, Haitao
, p. 7857 - 7859 (2013)
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.
