6/2/2023 0 Comments Quantum dot core shell![]() Recently, the core/shell structure of CdSe xS 1− x QDs was explored using XANES and EXAFS. ![]() X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) are sensitive to the oxidation state/site symmetry of elements and to the local structure around a selected atom. Therefore, the understanding of the local structure of these QDs and their environments is still rudimentary. Because of the small scattering volume of CdSe/ZnS QDs, it is not possible to obtain any information using high-resolution X-ray diffraction (HRXRD). However, not all of these techniques can reveal structural properties. Recently, the structural evolution of the interfaces in CdSe/CdS and CdSe/Cd 0.5Zn 0.5S colloidal QDs was investigated using surface-enhanced Raman spectroscopy. The structure of core/shell/shell CdSe/ZnSe/ZnS QDs was also studied using photoluminescence spectroscopy. The CdSe/ZnS core/shell structure was elucidated using high-resolution TEM/STEM. Element sensitive transmission electron microscopy (TEM) studies have provided information about the CdSe core structure and the surrounding ZnSe shells. Many techniques have been used to determine information on their structural properties and ordering phenomena. Knowledge of the chemical and physical properties of semiconductor nanocrystals is a key issue in understanding the mechanisms of the dots formation and their position correlations. These core/shell QDs have been shown to be generally more robust against chemical degradation and photooxidation. ![]() To address these disadvantages, scientists have focused on the development of core/shell QDs, which incorporate a shell of wider band gap semiconductor materials around the QD cores. Among various semiconductor materials, CdSe has been most extensively studied because its size-dependent photoluminescence is tunable across the visible spectrum, but it is insufficiently stable and is sensitive to the processing conditions and the environment. The fundamental physical properties and potential applications of quantum dots include multiplexed labeling and tracking of cells or molecules in a biological environment, downshifting light for color engineering in solid-state lighting, illumination and displays, and single-photon sources. Over the last 30 years, a significant amount of research has been reported regarding quantum dot (QD) synthesis. Therefore, single-step injection-free synthesis could generate a nearly ideal core/shell structure of CdSe/ZnS QDs capped with an organic sulfur ligand. This means that different emission wavelengths are only due to the crystal size with single-step injection-free synthesis. Wurtzite CdSe is the main core structure with a Cd-Se bond length of 2.3 Å without phase shift. With XANES results and MS calculations, it is indicated that sphalerite ZnS capped with organic sulfur ligands should be the shell structure. Moreover, theoretical XANES spectra calculated by FEFF.8.20 are used to determine the structure of Se and S compounds. X-ray absorption fine structure spectra are used to determine the core/shell structure of CdSe/ZnS quantum dots. In this paper, a single-step injection-free scalable synthetic method is applied to prepare high-quality core/shell QDs with emission wavelengths of 544 nm, 601 nm, and 634 nm. Understanding the chemical and physical properties of core/shell nanocrystal quantum dots (QDs) is key for their use in light-emission applications.
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