Molecular insight into intrinsic-trap-mediated emission from atomically precise copper-based chalcogenide models

Abstract

Luminescent Cu-doped semiconductor nanocrystals have long played a pivotal role in the advancement of lighting and display technologies. The luminescence observed in colloidal copper-based I–III–VI nanocrystals is attributed to defect emission arising from donor–acceptor pair recombination of excited charge carriers. However, a detailed atomic-level exploration of how distinct chemical components precisely influence the defect position has remained challenging, primarily due to inherent local structural imprecision of the traditional I–III–VI nanocrystals. In this study, we have prepared a set of copper-containing I–III–VI metal chalcogenide nanoclusters, 1-CuInS, 1-CuGaS, and 2-CuGaS, serving as unique models to address the aforementioned issues. Interestingly, despite possessing an identical crystalline structure, 1-CuInS and 1-CuGaS exhibit significantly different photoluminescence behaviors. For comparsion, 1-CuGaS and 2-CuGaS, which share the same second building units but differ in structural configuration, demonstrate similar luminescence performance. More importantly, we found that the green emission observed in 1-CuInS likely stems from the radiative recombination of electrons migrating from shallow delocalized traps to copper-localized holes. In contrast, the red emission observed in both 1-CuGaS and 2-CuGaS is presumably due to the recombination of electrons originating from deeply localized traps with copper-localized holes. This disparity in trap sites appears to be highly dependent on the presence of trivalent metal ions (In³⁺ and Ga³⁺) within the clusters, and the hypothesis is further substantiated through photoluminescence characterization of 1-CuInGaS containing both In³⁺ and Ga³⁺ ions simultaneously. Furthermore, we have explored the impact of introducing Cd ions into 1-CuInS, which can alter the position of shallow delocalized traps and thereby fine-tune the luminescence properties. Our findings shed light on the intricate interplay of chemical composition and defect states in copper-containing I–III–VI nanoclusters, offering valuable insights into the optoelectronic properties of copper-based semiconductor nanocrystals.