Thermally assisted optical processes in InP/ZnS quantum dots

The utilization of InP-based biocompatible quantum dots (QDs) necessitates a comprehensive understanding of the structure-dependent characteristics influencing their optical behavior. The optimization of core/shell QDs for practical applications is of particular interest due to their reduced toxicity, enhanced photostability, and improved luminescence efficiency. This optimization involves analyzing thermally activated processes involving exciton and defect-related energy levels. This study investigates water-soluble colloidal InP/ZnS QDs with varying shell thicknesses and stabilizing coatings using temperature-dependent optical absorption (OA) and photoluminescence (PL). Our results indicate that all samples experience temperature-induced shifts in exciton absorption and luminescence peaks due to interactions with acoustic phonons. Despite the wide size distribution of nanocrystals, the halfwidth of the bands remains constant. We observe a temperature-dependent Stokes shift in InP/ZnS QDs, revealing the fine structure of exciton states across different configurations. Furthermore, our findings demonstrate common mechanisms underlying PL thermal quenching in these QDs, regardless of the shell thickness or coating type. Specifically, defect-related emissions arise from localized energy levels at the core/shell interface. At the same time, exciton PL quenching primarily occurs through thermally activated electron migration from the InP core to the ZnS shell. Overall, our study highlights the potential for tailoring the temperature response of InP/ZnS QDs by adjusting shell thickness, offering opportunities to optimize their performance for specific applications.