Shake and break-shaking-induced changes of size quantization in aggregated quantum dots

We show how simple mechanical agitation of precipitated CdSe quantum dot aggregates causes partially reversible color changes (clearly visible to the eye) in the absorption spectrum of the CdSe (about 4 nm size). The color changes, which are due to changes in size quantization, are not accompanied by change in quantum dot size. This phenomenon is explained by partial deaggregation of the precipitates, leading to reduced charge overlap between neighboring dots. Shaking was shown to result in a looser aggregate structure. It is suggested that CdSO ₃ particles (an initial product of the CdSe formation reaction) act as weak bridges between CdSe quantum dots, mediating the interparticle interactions and allowing the deaggregation to occur on shaking.