Hydrothermal synthesis for high-quality glutathione-capped CdxZn1 – xSe and CdxZn1 – xSe/ZnS alloyed quantum dots and its application in Hg(II) sensing

High-quality Cd x Zn 1 – x Se and Cd x Zn 1 – x Se/ZnS core/shell quantum dots (QDs) emitting in the violet–green spectral range have been successfully prepared using hydrothermal methods. The obtained aqueous Cd x Zn 1 – x Se and Cd x Zn 1 – x Se/ZnS QDs exhibit a tunable photoluminescence (PL) emission (from 433.5 nm to 501.2 nm) and a favorable narrow photoluminescence bandwidth [full width at half maximum (FWHM): 30–42 nm]. After coating with a ZnS shell, the quantum yield increases from 40.2% to 48.1%. These Cd x Zn 1 – x Se and Cd x Zn 1 – x Se/ZnS QDs were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. To further understand the alloying mechanism, the growth kinetics of Cd x Zn 1 – x Se were investigated through measuring the fluorescence spectra and X-ray diffraction spectra at different growth intervals. The results demonstrate that the inverted ZnSe/CdSe core/shell structure is formed initially after the injection of Cd 2 + . With further heating, the core/shell structured ZnSe/CdSe is transformed into alloyed Cd x Zn 1 – x Se QDs with the diffusion of Cd 2 + into ZnSe matrices. With increasing the reaction temperature from 100 °C to 180 °C, the duration time of the alloying process decreases from 210 min to 20 min. In addition, the cytotoxicity of Cd x Zn 1 – x Se and Cd x Zn 1 – x Se/ZnS QDs were investigated. The results indicate that the as-prepared Cd x Zn 1 – x Se/ZnS QDs have low cytotoxicity, which makes them a promising probe for cell imaging. Finally, the as-prepared Cd x Zn 1 – x Se/ZnS QDs were utilized to ultrasensitively and selectively detect Hg 2 + ions with a low detection limit (1.8 nM).