Abstract
In their recent article, Owen et al. published a new dataset for ZnS quantum dots, linking optical band gap with nanocrystal diameter 1. Such bandgap/size datasets have been very helpful in the field of quantum dots to build calibration or sizing curves. These sizing curves are widely used to quickly determine nanocrystal sizes from absorption measurements, and they have been reported for a large variety of materials. The sizing of ZnS quantum dots, however, has always suffered from the low contrast this material provides in bright field transmission electron microscopy (TEM), which is the most common technique for measuring nanocrystal dimensions. In this regard, the work presented by Owen and coworkers is remarkable, both from a synthesis and a characterization perspective. Quasispherical ZnS quantum dots are formed across a broad diameter range, and sized by high-angle annular dark-field scanning transmission electron microscopy (STEM) and pair distribution function (PDF) analysis of X-ray scattering. On the other hand, the optical band gap of the nanocrystals was determined from their UV-vis absorption spectra as it is routinely done for this purpose. Finally, the authors fitted their dataset using a function that adds the inverse of a second-order polynomial to the bulk band gap energy.