Excitation intensity dependence of plasmonic enhancement of energy transfer between quantum dots

We studied the impact excitation power on the plasmonic enhancement of Forster resonance energy transfer (FRET) between CdSe/ZnS colloidal dots. We showed that when such quantum dots (QDs) were in the vicinity of metallic nanoparticles (MNPs), with the increase of the excitation laser intensity the spectral width of their emission was initially increased and then decreased, reaching its original value when the laser intensity was low. Such a spectral lineshape recovery happened while the emission peak wavelength of the quantum dots underwent a significant amount of red shift. By tuning the exciton–plasmon coupling strength and including the effects of the heat generated by plasmonic absorption, we showed that these results could be explained in terms of transition from a donor-dominated spectrum at low laser intensity to an acceptor-dominated one at high laser intensity. This suggests that excitation intensity can increase the rate of FRET between colloidal QDs when they are in close proximity to MNPs. (paper)