Synthesis and characterization of high-quality water-soluble near-infrared-emitting CdTe/CdS quantum dots capped by N-Acetyl-L-cysteine via hydrothermal method

The synthesis of water-soluble near-infrared (NIR)-emitting quantum dots (QDs) in aqueous solution has received much attention recently. However, the stabilizer 3-mercaptopropionic acid, commonly used in the synthesis of NIR-emitting QDs, is notorious for its toxicity and awful odor. Here we chose thiol ligand N-acetyl- L-cysteine (NAC) as the ideal stabilizer and have successfully employed it to synthesize high-quality NIRemitting CdTe/CdS QDs in a one-step process via a simple hydrothermal route. NAC possesses favorable properties such as nontoxic, nonvolatile, inexpensive, and good water-solubility. Our as-prepared NIR-emitting CdTe/CdS QDs exhibit high photoluminescence quantum yields (45-62%), narrow full-width at half-maximum, and high photostability, thanks to the formation of a protective CdS shell on the CdTe core through the decomposition of NAC in the hydrothermal route under high temperature. The prepared QDs can be applied for bioimaging due to its excellent water-solubility and biological compatibility. The core/shell structure of the NIR-emitting CdTe/CdS QDs was verified by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray powder diffraction. The formation mechanism of these QDs is discussed in detail.