Spectrally Resolved Kinetics of Energy Transfer Within a Single Emission Band of Highly Luminescent Thick-Shell CdSe/CdS Colloidal Quantum Dots

The resonant energy transfer (ET) between quantum dots (QDs) can influence the performance of some devices, such as QD light-emitting diodes (QLEDs). Since the ET efficiency decreases as a function of donor-acceptor distance, QDs of the thick shell allow reducing its impact. However, synthesizing thick-shell QDs of narrow, symmetric size distribution is challenging. This article shows that too broad size distribution can result in ET, even for QDs characterized by a thick shell, high quantum yield, and narrow emission spectrum. The impact of ET may remain undetected by standard spectroscopic characterization methods since ET occurs mainly from the blue tail of the luminescence spectrum. Here, ET is investigated for CdSe/CdS QDs characterized by a thick shell and high photoluminescence (PL) quantum yield. It is shown that despite the thick shell significantly limiting the ET efficiency at the maximum of the PL band, the ET at higher emission energies is clearly observable. Finally, a new parameter describing the non-single exponential shapes of PL decay curves is introduced. It is shown that such a parameter helps to study ET phenomena, allowing to collect all important information regarding the non-single exponential character of PL decays on a single graph.