Experimental verification of Förster energy transfer between semiconductor quantum dots

In recent years, energy transfer (ET) using semiconductor quantum dots (QDs) is getting increased attention. However, it has been postulated that ET between QDs is based on the F\"orster model, which is a well-established model of ET mechanism in organic dye systems, without verification. In this work, we have investigated ET mechanism in colloidal CdS QDs measuring photoluminescence dynamics of a bilayer structure consisting of differently sized CdS QDs. In the bilayer structure, the distance between the monolayer of donor QDs and that of acceptor QDs was controlled precisely by a spacer layer that is layer-by-layer assembly of polyelectrolytes. The bilayer structure enabled us to systematically measure the spacer-layer dependence of photoluminescence dynamics reflecting the ET process between QDs. It is demonstrated that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction, which verifies the appropriateness of the F\"orster model.