Reasoning the Photoluminescence Blinking in CdSe–CdS Heteronanostructures as Stacking Fault-Based Trap States

Minimizing the lattice mismatch of the semiconductor couple (e.g., CdSe/CdS) is an optimal approach for designing defect-free heterojunction nanostructures with bright emission. Spherical core/shell nanocrystals of CdSe/CdS, which can lead to near-unity photoluminescence quantum yields (ϕPL), have been well-explored; however, investigations on anisotropic nanostructures are rather limited. Typically, anisotropic shelling proceeds faster with a high possibility of defect state formation. To address this, herein, the photophysical properties of one-dimensionally grown CdS on CdSe seeds (CdSe–CdS), having a tapered end, are investigated as a function of shell length. Single-particle photoluminescence intensity studies revealed a decrease in the ON-to-OFF ratio on elongation and established the occurrence of trap-induced Auger processes. The fast growth of the shell results in phase mixing-induced stacking faults in CdS, creating trap states. The existence of these trap states in CdSe–CdS is further ascertained using HRTEM, and their density increases on elongation with a consequent decrease in ensemble ϕPL and enhanced blinking. The mechanistic insight presented herein provides valuable directives for the design of heteronanostructures with favorable luminescence attributes.