Evolution of Energy Transfer Process between Quantum Dots of Two Different Sizes during the Evaporation of Solvent

CdSe quantum dots (QDs) of two different sizes were dispersed in toluene solvent. We observed that the photoluminescence (PL) intensity of smaller QDs was gradually depressed by larger QDs during the evaporation of solvent. This is attributed to fluorescence resonance energy transfer (FRET) between two different sized QDs, when the distance between QDs is enough small to ensure close proximity. From PL intensity ratio of smaller to larger QDs, three stages can be distinguished during the evaporation and FRET rate begin to increase in the gel like stage. We estimated the mean distance variation between smaller and larger QDs during the evaporation from PL measurement and Dexter theory. In the solid resulted from the evaporation, FRET rate from smaller to larger dots and FRET rate within smaller QDs were quantitatively estimated to be 0.13 and 0.08 ns(-1), respectively. The change in PL properties due to the aggregation of QDs by evaporation is discussed.