Optimal mixture of randomly dispersed quantum dots for optical excitation transfer via optical near-field interactions

We theoretically and experimentally investigated a system composed of a mixture of different-sized quantum dots involving optical near-field interactions to effectively induce optical excitation transfer. We demonstrated that the ratio of the number of smaller quantum dots to larger ones can be optimized using a density-matrix formalism so that excitons generated in the smaller ones are efficiently transferred to the larger ones. We also describe experimental demonstrations based on a mixture of 2 nm- and 2.8 nm-diameter CdSe/ZnS quantum dots dispersed on the surface of a silicon photodiode, where the increase in induced photocurrents due to optical excitation transfer is maximized at a certain quantum dot mixture which agrees with theoretical calculations.