Hydrothermal synthesis of high-quality type-II CdTe/CdSe quantum dots with near-infrared fluorescence

A simple hydrothermal method is developed for the synthesis of high-quality, water-soluble, and near-infrared (NIR)-emitting type-II core/shell CdTe/CdSe quantum dots (QDs) by employing thiol-capped CdTe QDs as core templates and CdCl2 and Na2SeO3 as shell precursors. Compared with the original CdTe core QDs, the core/shell CdTe/CdSe QDs exhibit an obvious red-shifted emission, whose color can be tuned between visible and NIR regions (620–740 nm) by controlling the thickness of the CdSe shell. The photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to 44.2% without any post-preparative treatment. Through a thorough study of the core/shell structure by high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–vis) absorption spectra, fluorescence spectra, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the as-prepared CdTe/CdSe QDs demonstrate good monodispersity, hardened lattice structure and excellent photostability, offering a great potential for biological application.

Schematic illustration of the preparation of CdTe/CdSe core/shell QDs (a) and their pictures observed under the radiation of an ultraviolet lamp (b) and the corresponding fluorescence spectra (c).Figure optionsDownload high-quality image (155 K)Download as PowerPoint slideResearch highlights
► The quantum yield of near-infrared-emitting CdTe/CdSe QDs reach up to 44.2%.
► This strategy is more efficient and convenient by employing hydrothermal technique.
► Sodium selenite was employed as selenium source.
► The as-prepared QDs possess small size and excellent photostability.