Size Dependent Resonance Energy Transfer between Semiconductor Quantum Dots and Dye Using FRET and Kinetic Model

In the present study, we demonstrate the size dependent resonance energy transfer from CdSe QDs (donor) to Nile Red dye (acceptor) using steady state and time-resolved spectroscopy. A strong evidence of size dependent efficient resonance energy transfer between CdSe QDs and dye molecules is observed. Using the Förster theory, the calculated energy transfer efficiencies from QD to dye are 8.4, 13.8, and 51.2% for 2.4 nm CdSe, 2.9 nm CdSe, and 3.3 nm CdSe, respectively. A stochastic model for the kinetics of energy transfer from CdSe QDs to Nile Red dye molecules has been proposed to understand the interaction between excited states of CdSe QDs with dye molecules. By analyzing time-resolved fluorescence decay curves of CdSe QDs in the absence and in the presence of Nile Red dye, the values of the rate constant ( k q ) for energy transfer per one dye molecule and the efficiency (ϕ ET ) of quenching have been calculated. The estimated energy transfer rates are 0.002, 0.016, and 0.038 ns −1 for 2.4 nm CdSe, 2.9 nm CdSe, and 3.3 nm CdSe QDs, respectively, which are well matched with FRET data.