Dependence of Short-Range Energy Transfer Behavior on the Average Distance between Colloidal Quantum Dots in Solutions: Implications for Resonance Energy Transfer

High Resolution Image Download MS PowerPoint Slide For the applications of color conversion and the characterization of colloidal quantum dots (QDs), we use three series of solution samples of surface-charged QDs for studying the dependence of resonance energy transfer (RET) behavior on QD concentration or average QD distance. The mixture samples of green-emitting QD, i.e., donor, and red-emitting QD, i.e., acceptor, and the reference samples of single-type QD are prepared for investigating the RET behavior. The variations of RET efficiency, RET rate, and red-overgreen intensity ratio with average QD distance under the three conditions of different relative surface charges and different relative concentrations are compared. A theoretical model for the dependence of normalized RET rate on average QD distance is derived to show the reduced inverse-proportion power index in such a multiple-acceptor RET system. However, this model is applicable only when the average QD distance is larger than ∼50 nm under the condition of the same surface charge on the donor and acceptor. When the average QD distance is smaller than ∼50 nm, the effects of excitation shielding, electrostatic force, and multiple-donor/multiple-acceptor interaction further reduce the inverse-proportion power index. Under the condition of the opposite surface charges, a small inverse-proportion power index can always be observed irrespective of the average QD distance, which is attributed to the attraction between the donor and acceptor, i.e., a QD distribution with small distances between a donor and a few acceptors even though individual donors are far apart.