Ultra-small stable quantum dots (essentially extremely tiny particles that confine even the free electrons in them rather well) are very interesting for a wide range of applications. However using them for applications requires them to be of essentially the same size which is rather hard. However Niya Mary from our group discovered a size focusing mechanism in ceramc systems (ZnO to be precise). Bhusankar from the group has extended this result to copper oxide as well. However unlike ZnO; down at this size regime Cu seems to flip-flop between two different oxidation states. Fascinatingly the usual formula that works for quantum dots does not work for our materials; we suspect this has to do with the nature of Cu in these systems (i.e it being of multiple oxidation states; namely a mix of +1 and +2).

Ongoing efforts indicate that the size-focusing approaches we have developed are primarily dependent on specific interactions between the Cu atom and the surface-active agent (called hard-hard-acid-base interactions) used in this process; the solvent we use matters too.

In fact there are ongoing theoretical and computation efforts to develop predictive models for this process so that the experiments may be intelligently designed.

Ref: Bhusankar Talluri, Edamana Prasad, and Tiju Thomas, "Ultra-small (r<2 nm), stable (>1 year), mixed valence copper oxide quantum dots with anomalous band gap", arXiv:1706.01261 (2017)