One-pot synthesis of CdSe magic-sized nanocrystals using selenium dioxide as the selenium source compound

• Selenium dioxide was first used as Se source compound for one-pot synthesis of CdSe MSQDs.
• Two pure MSQDs families were synthesised in a wide range of temperature and Cd-to-Se feed ratio.
• N-oleoylmorpholine plays three roles of reaction medium, reductant of SeO2, and stabilizer of QDs.
• No other ligands such as fatty acids or phosphines were added.
• The degree of supersaturation impacted the presence of CdSe NCs with different sizes.

CdSe magic-sized quantum dots (MSQDs) families 392 (F392) and 461 (F461) exhibiting bright band gap emission and little trap emission were synthesised via a non-injection one-pot approach, where cadmium acetate dihydrate (Cd(OAc)2·2H2O) and selenium dioxide (SeO2) were used as Cd and Se source compounds, respectively, and N-oleoylmorpholine was selected as reaction medium. The approach does not have to adding any long-chain fatty acid or phosphine ligands. The investigation showed that N-oleoylmorpholine played three roles of reaction medium, reductant of SeO2, and stabilizer of QDs. The reduction reaction step of SeO2 to Se0 was important to the regulation and control of the reactivity of Se precursors as well as the thermodynamic equilibrium between nucleation and dissociation of the nuclei. The parameters including the reaction temperature, Cd-to-Se feed molar ratio, and growth periods were investigated. The synthetic approach allowed long-term growth and stability of CdSe MSQDs in a wide range of temperature and Cd-to-Se feed molar ratios. Different families developed independently from different nuclei. The degree of supersaturation (DSS) impacted the presence of CdSe NCs with different sizes. The moderate DSS favored the common development of different species coexisting in the same batch, the relatively high DSS favored the long-term existence of CdSe MSQDs family with high thermodynamically stability. New growth protocol was proposed to explain the formation mechanism of CdSe MSQDs. The characterization of CdSe MSQDs by the transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) have been also accomplished.