Phosphine-free synthesis of Zn1-xCdxSe/ZnSe/ZnSexS1-x/ZnS core/multishell structures with bright and stable blue-green photoluminescence

Highly photoluminescent (PL) Zn1-xCdxSe/ZnSe/ZnSexS1-x/ZnS core/multishell nanocrystals were successfully synthesized by a phosphine-free method. Alloyed ZnSexS1-x was chosen as the shell material to epitaxially grow on pre-synthesized Zn1-xCdxSe nanocrystals. By decreasing the molar ratio between Se and S in ZnSexS1-x, the shell composition gradually changed from ZnSe to ZnS. The PL emissions of these core/multishell nanocrystals can be tuned from 450 to 530 nm. The PL quantum yields (QYs) of as-synthesized nanocrystals reached 50 to 75% with full width at half maximum (FWHM) between 28 and 45 nm. By an organic-aqueous phase transfer method, such core/multishell nanocrystals can be transferred into water successfully using an amphiphilic oligomer (polymaleic acid n-hexadecanol ester) as a surface coating agent. It was found that the shell thicknesses of the assynthesized core/multishell nanocrystals dramatically affected the phase transfer efficiency. Stability tests showed that the water-soluble Zn1-xCdxSe/ZnSe/ZnSexS1-x/ZnS core/multishell nanocrystals with 10 monolayers of shells had very high PL QY and stability in various physiological conditions.