Role of Aspect Ratio in the Photoluminescence of Single CdSe/CdS Dot-in-Rods

The elongated shape of CdS nanorods enables linearly polarized photoluminescence (PL) emission from the core/shell CdSe/CdS dot-in-rod (DR) nanocrystals. This work unravels the role of aspect ratios of CdS nanorods in the PL emission of single CdSe/CdS DRs using single-dot PL spectroscopy. We find that as the aspect ratio increases, the PL quantum yield and lifetime significantly reduce, but the PL blinking is suppressed, and the effect on the PL spectrum is less. The correlation between the degree of polarization and the aspect ratio is modeled by calculating the band-edge exciton fine structure. We find that when the aspect ratio reaches 7, the contribution of the dielectric effect induced by the elongated CdS nanorods to the degree of polarization becomes limited. The aspect ratio has a negligible influence on the electronhole exchange interaction eta. The net-splitting Delta between the heavy-hole and light-hole valence sub-bands, on the other hand, can be significantly changed from 13 to -17 meV through the strain effect between the core and the shell in DRs of different aspect ratios, thereby increasing the degree of polarization.