Abstract: In this study, a two-step method was used to synthesize highly luminescent AgGaS/ZnS/ZnS quantum dots (QDs). In the first step, an inner ZnS shell was formed via a one-pot method, which resulted in a smaller lattice mismatch between the AgGaS core and the outer ZnS shell, thereby facilitating the formation of a thick outer shell. After the two-step shelling process, the synthesized AgGaS/ZnS/ZnS QDs showed an excellent photoluminescence quantum yield (PLQY) of 96.4% with a peak wavelength of 508 nm, representing the highest PLQY reported thus far for AgGaS QDs. Furthermore, the effect of halogen ions in Zn precursors on the shelling process was investigated. It was proposed that the capacity of halogen ions to coordinate with the QDs influenced the balance between Zn cation diffusion and ZnS shelling reaction. Specifically, the ZnS shelling reaction was dominant when ZnCl₂ was employed, while Zn cation diffusion was the dominant process under the I^--rich environment. This work provides insights into the interfacial restructuring during the ZnS shelling and offers a clear map for the tailored synthesis of core/shell QDs.

Key words: AgGaS, Quantum dots, Photoluminescence, Core/shell, Alloyed core/shell interface