Quantifying Quantum Dots through Förster Resonant Energy Transfer

Semiconductor nanocrystals (NCs or quantum dots) have significant potential for use in a variety of applications from renewable energy generation to biological imaging. Modern methods of colloidal synthesis can be used to create crystalline materials with tight size distributions; this assures high quantum yields and narrow emission profiles in the case of direct-bandgap semiconductors. The optical properties of NCs may also be tuned with size due to quantum confinement effects. Quantum confinement also creates problems when characterizing nanomaterials; specifically, the absorptivity of a sample is a function of the size and structure of the quantum dots. We demonstrate here a simple method for determining the molar absorptivity of aqueous CdSe/CdZnS NCs through Forster resonant energy transfer. Energy transfer from NC donors to dye acceptors was measured and modeled using standard Forster theory incorporating Poissonian statistics to calculate the acceptor/donor ratio leading to a direct determination o...