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

Abstract

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 electron−hole exchange interaction η. The net-splitting Δ 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.

Charge and energy transfer dynamics in single colloidal quantum dots/monolayer MoS2 heterostructures

“…The normalized on-and off-time probability densities [45][46][47] are the fingerprint of QD blinking studies to investigate and compare the blinking activities of single QDs on silicon and monolayer MoS 2 . According to the two peaks of PL intensity histograms in Fig.…”

Uniaxial Strain Engineering via Core Position Control in CdSe/CdS Core/Shell Nanorods and Their Optical Response

“…The splitting is comparable to thermal energy at room temperature, resulting in a thermal population of holes across all four bands . However, uniaxial strain along the c -axis is known to energetically red-shift light hole states more significantly than heavy hole states, and the light hole state becomes the ground state of CdSe NC cores in core/shell NRs. ,,, If the anisotropic strain is strong enough, the splitting of the band-edge states can become larger than the thermal energy, lifting the state degeneracy.…”

“…3 CdSe/CdS dot-in-rod structures have been widely investigated. 8,13,15,17,20,21 A CdSe core embedded in a prolate or rod-shaped CdS shell contracts along the c-axis, imposing uniaxial compression on the CdSe core. However, only weak uniaxial strain is typically realized in such structures.…”

Electronic Structure and Excited State Dynamics of Cadmium Chalcogenide Nanorods

“…In Section we described calculations which show that strain is an important factor generating a NR-like electronic structure in DiRs. This is consistent with polarization measurements where increasing rod lengths increase the system strain,and result in more polarized emission. , Beyond aspect ratio alone, the position of the core within the NR also matters. If the core is positioned all the way at one end, the relatively short rod component in that direction reduces the PL polarization due to a weakly polarized field in that direction …”

“…While trapping-induced type-B blinking has been shown to be dominant in CdSe NRs, − , in CdSe NR heterostructures, type-A blinking, which can be due to either charging or trapping, has been reported in addition to type-B blinking. ,, In particular, type-A blinking due to a charging mechanism has been shown in CdSe/CdS DiRs via fluorescence lifetime-intensity distribution (FLID). , Separately, aspect-ratio-dependent CdSe/CdS DiR blinking studies showed reduced type-A blinking for longer NRs, which the authors ascribed to reduced wave function overlap with trap states, suggesting a trapping-induced blinking mechanism. In this case, the core size and shell thickness were kept relatively constant, and only the shell length was increased to tune the aspect ratio.…”