Aqueous Synthesis of Zinc Blende CdTe/CdS Magic-Core/Thick-Shell Tetrahedral-Shaped Nanocrystals with Emission Tunable to Near-Infrared

Abstract

We demonstrate the synthesis of near-IR-emitting zinc blende CdTe/CdS tetrahedral-shaped nanocrystals with a magic-sized (approximately 0.8 nm radius) CdTe core and a thick CdS shell (up to 5 nm). These high-quality water-soluble nanocrystals were obtained by a simple but reliable aqueous method at low temperature. During the growth of the shell over the magic core, the core/shell nanocrystals change from type I to type II, as revealed by their enormous photoluminescence (PL) emission peak shift (from 480 to 820 nm) and significant increase in PL lifetime (from approximately 1 to approximately 245 ns). These thick-shell nanocrystals have a high PL quantum yield, high photostability, compact size (hydrodynamic diameter less than 11.0 nm), and reduced blinking behavior. The magic-core/thick-shell nanocrystals may represent an important step toward the synthesis and application of next-generation colloidal nanocrystals from solar cell conversion to intracellular imaging.

A New Class of Nanostructured Inorganic–Organic Hybrid Semiconductors Based on II–VI Binary Compounds

“…Remarkably, the extent of such band gap increase ($2 eV) is significantly higher than what has been achieved by the smallest colloidal QDs reported to date ($1 eV) (72,(117)(118)(119)(120). Compared with the colloidal II-VI quantum dots, the crystalline nanostructured hybrid semiconductors are free of several crucial issues [e.g., particle size distribution and morphology, postsynthetic purification, stoichiometric lattice (problems with lattices altered by the defects, e.g., excess atoms, alloying additions, or vacancies), local oxygen concentrations, as well as the dispersity of particles].…”

“…As shown in Table VIII, the thickness of the II-VI single layers in hybrid structures is typically $4-5 A , which is much smaller than the average dimensions of colloidal QDs. Thus, the extent of quantum confinement in hybrids (except for Mn based and double-layered structures) is evidently much stronger than that found in the smallest QDs reported to date (72,(117)(118)(119)(120)178). Theoretical calculations using density functional theory (DFT) with local density approximation (LDA) have been carried out on selected hybrid structures to confirm this observation (179,180).…”

Quantum Dots in Bioanalysis: A Review of Applications across Various Platforms for Fluorescence Spectroscopy and Imaging

“…[68][69][70] The possible exception is the aqueous synthesis of CdTe QDs, where quantum yields have been reported to reach 82% but are typically closer to 40%. [71][72][73] These QDs can also be relatively monodisperse, with FWHM values typically in the range of 30-60 nm.…”

Photothermal Spectroscopic Characterization in CdSe/ZnS and CdSe/CdS Quantum Dots: A Review and New Applications

“…As a comparison, for Rhodamine B dye dissolved in methanol, the  values decreased from 0.8 to ~0.1 with increasing concentration in the range of ~10 -5 -10 -3 molar (Bindhu et al, 1996). For CdSe/ZnSe core/shell nanocrystals suspended in organic solvents, the values of = (0.60-0.85) were obtained, as a result of the thicker deposit shell concentration (Reiss et al, 2002); quantum yield values were reported as 0.4-0.6 for CdSe QDs (core-sizes between 2.8 and 5.0 nm), 0.55 for CdSe/ZnSe/ZnS (Donegá et al, 2006) and up to 0.70 for CdTe/CdS MSNs aqueous colloidal solution (Deng et al, 2010).…”

“…The colors of the solutions are illustrative. (Chen et al, 2008;Deng et al, 2010), and the value of < em >= 588.9 nm for = 1.25 cm -1 at 514.5 nm was obtained from fluorescence measurement. Peaks related to longitudinal optical phonons (LO) and (2LO) at 206.6 and 411 cm −1 of the synthesized CdSe MSNs are clearly observable in the Raman spectrum shown in Fig.…”