1,721,632 research outputs found
Accurate, Precise, and Verifiable Photoluminescence Efficiency of Colloidal Quantum Dots Sols by Photothermal Threshold Quantum Yield Analysis
No full textColloidal quantum dots (QDs) have become multipurpose luminophores that combine a broad excitation with a narrow emission spectrum. Applications in displays, lighting, or solar-energy conversion, however, require quantum dots that have a photoluminescent quantum yield (PLQY) approaching unity. This need makes the accurate, precise, and verifiable determination of the photoluminescence efficiency of QDs of utmost importance for the field. Here, we describe photothermal threshold quantum yield as a calorimetric method for measuring the PLQY of QDs in liquid dispersions. Taking the example of InP-based core/shell QDs, we detail the principles behind the analysis, and we benchmark results relative to the spectroscopic determination using an absolute PLQY measurement with an integrating sphere. We argue that the accuracy of the method for highly efficient emitters, and the simplicity of the data and the data analysis make photothermal threshold quantum yield well suited for certifying the photoluminescence efficiency of QDs.P.S. acknowledges VLAIO (O&O ReQLED2020) and FWOVlaanderen (12A9123N) for research funding. Z.H. acknowledges the FWO-Vlaanderen (research project G0B2921N), Ghent University (BOF-GOA 01G02124) and Catalisti (cSBO NaPoly) for research funding. S.M. and KV acknowledge the European Research Council (ERC, grant agreement 864625) and Hasselt University (BOF19OWB15)
Classical Force Field Parameters for InP and InAs Quantum Dots with Various Surface Passivations
No full textClassical molecular dynamics (MD) simulations on realistic colloidal quantum dot (QD) systems are often hampered by missing force field (FF) parameters for an accurate description of the QD-ligand interface. However, such calculations are of major interest, specifically for studying the surface chemistry of colloidal nanocrystals. In this work, we have utilized a previously published stochastic optimization algorithm to obtain FF parameters for InP and InAs QDs capped by Cl, amine, carboxylate, and thiolate ligands. Our FF parameters are interfaced with well-established FFs for organic molecules, allowing for the simulation of InP and InAs QDs with a broad range of organic ligands in explicit apolar solvents. The quality of our FF parameters was assessed by comparing properties of the classical MD simulations with ab initio MD simulations and experimental and theoretical values from the literature
Synthesis and self-assembly of colloidal quantum dots
No full textIn this work, we study the synthesis and self-assembly of colloidal quantum dots (QDs). First, the InP and CdSe QDs are synthesized using the hot-injection synthesis procedure, and the optical and crystallographic properties are characterized via UV-vis absorbance and photoluminescence spectroscopy and X-ray diffraction. The photoluminescence properties of the CdSe dots are optimized by surrounding the particles with a CdS or ZnS shell. The particles are further characterized via Transmission Electron Microscopy (TEM). Nuclear Magnetic Resonance is used to access information about the ligand molecules which stabilize the particles. Next, the possibilities of Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) deposition are explored to produce QD monolayers and multilayers. The layer quality is assessed via Atomic Force Microscopy, Scanning Electron Microscopy and TEM. We see that the LS and LB techniques both yield excellent mono- and multilayers, although LS deposition yields different results on hydrophilic and hydrophobic substrates. Combination of LB or LS deposition with optical lithography yields micropatterned layers. Also phase transitions of Langmuir layers upon compression beyond the collapse pressure are studied, and a thermodynamic model for the transitions is suggested. Finally, the effects of Atomic Layer Deposition of aluminium oxide layers on the photoluminescence properties of the QD layers is studied
Colloidal nanocrystals, a study on more efficient synthesis and deposition methods
No full textColloidal nanoparticles gained great interest due their size dependent optical properties. Several synthesis methods have been developed to improve the environmental impact of the chemical used. However these procedures bases mainly on homogeneous ODE-Se also show limitation regarding the yield and the tuning of optical properties. In the thesis an approach based on the use of a heterogeneous ODE-Se is investigated. The new precursor leads to high yield reactions as well as high tenability of the particle size. The new precursor has been used also to obtain homogeneous Cd(S,Se) alloys increasing in this way the degree of freedom in the tuning of the emission wavelength. Core/shell quantum dots have been studied to improve the luminescence properties of the particles. In particular a new method has been developed to overcome the time limitation imposed by the reactions commonly used in literature to create such structures. This method consists in a seed growth of core/shell quantum dots in a time span of few minutes and shell thickness up to 15 monolayers. Colloidal CdSe quantum dot shave been also investigated to understand the charging dynamics that lead to solution with a fraction of the particles carry a positive or negative charge. Finally iron oxide nanocrystals are synthesized, deposited and used as catalyst for the growth of carbon nanotubes, creating a flexible system that can optimize the different phases of the process in an independent wa
Red-emissive nanocrystals of Cs4MnxCd1-xSb2Cl12 layered perovskites
No full textLayered double perovskites are currently being investigated as emerging halide-based materials for optoelectronic applications. Herein, we present the synthesis of Cs4MnxCd1-xSb2Cl12 (0 <= x <= 1) nanocrystals (NCs). X-ray powder diffraction evidences the retention of the same crystal structure for all the inspected compositions; transmission electron microscopy revealed monodisperse particles with a mean size between 10.7 nm and 12.7 nm. The absorption spectra are mostly determined by transitions related to Sb3+, whereas Mn2+ induced a red emission in the 625-650 nm range. The photoluminescence emission intensity and position vary with the Mn2+ content and reach the maximum for the composition with x = 0.12. Finally, we demonstrate that the photoluminescence quantum yield of the latter NCs was increased from 0.3% to 3.9% through a post-synthesis treatment with ammonium thiocyanate. The present work expands the knowledge of colloidal layered double perovskite nanocrystals, stimulating future investigations of this emerging class of materials
Near infrared heteronanocrystals with enhanced electro-optical properties : from synthesis to layer formation
Full text linkSynthesis of nanocrystals actived in the near infrared and study of their opto-electronic properties
Towards ZnSe into lighting applications : study of synthesis mechanism and surface properties
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