Influence of Core Localization on the Electron Dynamics of CdSe/CdS Dot-in-Rod Heterostructures

Nanoscale semiconductor heterostructures are solid states platforms where a variety of potential physical phenomena converge. These endows them with unique optical and electron properties of interest for both fundamental and applied fields of science. Some examples are high photoluminescence quantum yield, QY, high nonlinear optical responses, and control over exciton dynamics, among other. All of these being controllable by the nanostructure size (due to quantum confinement effects), composition and shape. Among the large family of heterostructures, the CdSe/CdS dot-in-rods (DinRs), a CdS rod-shaped shell seeded by a CdSe quantum dot, have attracted great attention, given their mixed dimensionality (0D core and quase-1D shell). In DinRs the CdS shell highly enhances the absorption cross sections, through which charge carriers diffuse until they reach the core region, where emission occurs. This is an effect of the band alignment, which can be of type-I or quasi-type-II, depending on the relative core and shell diameters (according to the CdSe and CdS exciton Bohr radii). Even though some properties of DinRs are well-understood, a deeper understanding of the influence of core localization on the exciton dynamics is still missing. The main reason is that only in the last years it was possible to implement control over the core position on the synthesizes process . Here, we present a study of the effect of core localization on the intraband dynamics, electron-phonon interactions, and multi-exciton dynamics of DinRs with different band alignments, and core localization (core is put at the center, at the edge, and at positions in between). The results show that single-exciton, biexciton and negative trion decay dynamics are slowed down as the core is moved away from the center for all samples except for the case of weak confinement regime, where there is an inversion of the dependence, i. e. multi-exciton recombination is speeded up as the core is moved from the center. Indicating complex exciton dynamics in DinRs. Using a multi-dimensional coherent spectroscopy setup, we also investigate the influence of the core localization on the exciton-phonon interaction, and how this influences the homogeneous linewidth and the zero-phonon line in DinRs.