Spectral and temporal photoluminescence behavior of colloidal PbS quantum dots

Abstract

We have studied a temporal and spectral behavior of the photoluminescence of the colloidal PbS quantum dots (QDs) with a controlled spacing between QDs. The high-speed streak camera system combined with a monochromator was used to obtain the time evolution of the luminescence spectrum itself.In the close-packed QD sample with a QD edge-to-edge spacing of 4.2nm, the two-step photoluminescence decay with time constants of 30 and 200ns was observed after initial fast change in the luminescence due to the fast energy transfer process. This two-step decay also occurred for the other QD samples with large QD edge-to-edge spacings, i.e., 5.8 and 12.5nm. Here, the observed decay time for these samples showed the same spectral behavior even though the distance between QDs is considerably different. Such characteristic photon energy dependence strongly suggests a decay mechanism that the decay consists of (1) fast non-radiative decay from the excited state to the ground state through surface defect states and (2) slow intrinsic radiative decay. Thus, these results indicate a new aspect of the photoluminescence decay characteristics, which shows the importance of the non-radiative energy transfer path in the PbS QD luminescence.