Universal "Mass-Method" for Precise Shell Coating of Quantum Dots by Mass and Size

Shell coating of quantum dots (QDs) is a widely implemented strategy to enhance the optical properties and stability. Typically, binary QDs, such as CdSe and CdS, are able to be precisely coated by several layers of shell material because their molar concentrations and radii could be empirically calculated from UV-vis absorption spectra. When it comes to ternary or alloyed QDs, such as CdSeS, there is not even one empirical formula to calculate them. Therefore, the method mentioned above is no longer available. However, complex alloyed QDs are prevalent in both research and industry since they exhibit more color gamut and tunability than binary QDs. Here, a "mass-method" was proposed to solve the problem of precise shell coating for complex alloyed QDs by mass and size (via TEM characterization). This method bypasses the necessity of the step of measuring the QD molar quantity before shell coating. After verification with CdSe and CdS QDs, this method was applicable with CdSeS alloyed QDs. The error of shell thickness coated onto the QD surface in this work was less than 0.1 monolayers. This work has filled the gap of precise shell coating for complex QDs, and it could be extended to any QD system.