Thickness and Temperature-Dependent Traits of CdSe/CdSeS Heterostructure Nanocrystals

Colloidal semiconductor nanocrystals (NCs) have been extensively studied for their tunable bandgap energy and outstanding optical properties. This research focuses on the synthesis of CdSe/CdSeS heterostructure nanocrystals (HNCs) with precisely controlled spherical morphologies. The synthesis process involved forming a CdSe core and subsequently coating it with a CdSeS shell through the gradual injection of sulfur (S) precursors, allowing the shell thickness to be finely adjusted between two and six monolayers. As the shell thickness increases, both the emission and absorption spectra systematically shift to lower-energy regions, thereby modifying the optical properties of the HNCs. A strong correlation is observed between the interfacial strain at the CdSe/CdSeS boundary and the shell thickness, which significantly affects the efficiency of HNCs. Temperature-dependent analyses reveal variations in emission energy with temperature, offering insights into the thermal behavior and resilience of these crystals. Anomalies in the temperature-dependent photoluminescence linewidth are attributed to carrier relaxation into local energy minima caused by interfacial strain. Compared with bare NCs, core-shell HNCs demonstrate enhanced coupling between excitons and both longitudinal optical phonons and acoustic phonons. This study highlights the critical role of shell thickness in fine-tuning the optical and thermal properties of CdSe/CdSeS HNCs, offering valuable insights for their potential applications in advanced technologies.