Effect of Gradient Alloying on Photoluminescence Blinking of Single CdS x Se1–x Nanocrystals

Alloyed CdS x Se1–x semiconductor nanocrystals (NCs) were obtained from a one-pot synthesis at reduced temperature with moderate quantum yield. Comprehensive structural characterizations of the CdSSe NCs reveal that the NCs have gradient alloyed structure, with Cd evenly distributed over the entire NC, Se rich in the center, and S rich in the outer region. This is due to the difference in the nucleation kinetics of S and Se precursors. Optical studies at the single NC level show that the NCs have reduced photoluminescence blinking, increased “on” time fraction, and good photostability, in comparison with CdSe NCs. The incorporation of sulfur composition in the alloy NCs improves surface passivation and in turn protects the NCs from (photo)­oxidation. The gradual change in the NC composition from center to outer regions creates a smooth “interface”, compared to core/shell NCs. These factors lead to reduced nonradiative rates in the NCs, improving their emitting properties.