Unveiling the Role of ZnCl₂ in Enhancing the Photoluminescence Efficiency of Amino-As-Based InAs@ZnSe Quantum Dots

High Resolution Image Download MS PowerPoint Slide We investigated how ZnCl 2, employed as an additive in the amino-As-based synthesis of indium arsenide (InAs) quantum dots (QDs), considerably improves the photoluminescence quantum yield (PLQY) of the resulting InAs@ZnSe core@shell QDs. We achieved this by synthesizing and comparing three distinct InAs QD samples and their corresponding core@shell structures: (1) In(Zn)As QDs (synthesized with ZnCl 2 ); (2) standard InAs QDs (std-InAs, made without additives); and (3) std-InAs QDs postsynthesis treated with ZnCl 2 (Zn–InAs). High PLQY values (∼70%) were attained only with In(Zn)As@ZnSe QDs, while std-InAs@ZnSe and Zn–InAs@ZnSe samples exhibited much lower PL efficiencies (10–20%). We also demonstrated that (i) the high PLQY in In(Zn)As@ZnSe QDs could not be attributed solely to the presence of an In–Zn–Se interlayer, as this was present in all three samples; (ii) the specific ZnSe shelling procedure had only a minor impact on the final PLQY; and (iii) the PL efficiency was significantly improved only when high amounts of ZnCl 2 additive (specifically with ZnCl 2:InCl 3 precursor ratios over 10:1) were used during the InAs QDs synthesis. These findings were rationalized through density functional theory (DFT) calculations coupled with X-ray absorption spectroscopy measurements. DFT models suggested that std-InAs QDs feature surface trap states, mainly located on the (−1–1–1) facets, thus low PL efficiency even after ZnSe shelling. The use of ZnCl 2 in the InAs synthesis led to surface Zn incorporation, particularly on the (100) and (−1–1–1) facets, effectively passivating surface traps and, consequently, yielding highly emissive In(Zn)As@ZnSe QD systems. In contrast, ZnCl 2 employed in the postsynthesis treatment of std-InAs QDs resulted only in a limited surface Zn incorporation and in ZnCl 2 adsorption on the (−1–1–1) facets (i.e., ZnCl 2 acting as a Z-type ligand), leading to poor passivation of surface traps. Overall, our study demonstrates the critical role of ZnCl 2 as a synthesis additive in delivering highly emissive amino-As-based InAs@ZnSe QDs.