Delocalized and localized charged excitons in single CdSe/CdS dot-in-rods revealed by polarized photoluminescence blinking

CdSe/CdS heterostructured nanocrystals with quasi-type-II band alignments provide an interesting platform for studying the photoluminescence (PL) blinking associated with their unique morphologies. By using simultaneous measurements of the PL intensity, lifetime, and polarization anisotropy, we reveal the role of the electron delocalization during the blinking of single CdSe/CdS dot-in-rods. We found that a significant change in the PL polarization anisotropy distinguishes between two kinds of charged excitons with different electron delocalizations. We report our observation of unique polarized PL blinking governed by the band alignments and the Coulomb interactions between the charges inside and outside the dot-in-rod.

Figure 1

(a) Transmission electron microscope image of a dot-in-rod sample and a schematic of its structure. (b) Detection geometry for measuring the polarization blinking. (c) Polarization-angle dependence of the PL intensity. (d) Coincidence counts as a function of the time delay. (e) An example of the PL intensity time traces showing multiple states. (f)–(h) Decay curves obtained for the data indicated by red, blue, and black arrows in (e).

Figure 2

(a) Time traces of the PL intensity obtained with the polarization parallel (black) and perpendicular (red) to the excitation polarization. (b) PL lifetime estimated for each binning time (200 ms) using the parallel polarization data in (a). (c) Time trace of the emission polarization calculated from the data in (a).

Figure 3

(a) FPID and (b) FLID plots of the data in Figs. 2–2. (c) Schematic illustration of the energy diagram of neutral excitons and charged excitons in a dot-in-rod sample with type-II band alignment. The introduction of an electron and the position of the ejected hole change the delocalization of the 1D electron.

Figure 4

(a) FPID and (b) FLID plots of data from another dot-in-rod sample. (c) Schematic illustration of the energy diagram of neutral excitons and charged excitons in a dot-in-rod sample with type-I band alignment.