One-pot aqueous synthesis of DHLA-capped CuInS₂ quantum dots with defect-mediated photoluminescence

Aqueous synthesis of I-III-VI₂ quantum dots (QDs) remains challenging due to variability associated with post-synthetic ligand exchange. Here, a direct one-pot aqueous synthesis of dihydrolipoic acid (DHLA)-capped CuInS₂ (CIS) QDs is presented, enabling simultaneous nanocrystal growth and surface passivation under mild conditions (75 °C) without ligand exchange. Ligand-control experiments using ligand-free and 3-mercaptopropionic acid (MPA)-capped CIS QDs confirm the role of DHLA in improving photoluminescence (PL) efficiency, colloidal stability, and chalcopyrite-related diffraction features. The optimized QDs exhibit sizes of 2.5-5.0 nm and broad defect-mediated PL centered at 580 nm, with a PL quantum yield (PLQY) of ~ 9%. Time-resolved PL (TRPL) analysis further supports long-lived donor-acceptor-type recombination involving In_Cu-related donor and V_Cu-related acceptor states. PL modulation by urea shows an approximately linear concentration-dependent response over 0-5.0 mM, with a sensitivity of 0.0850 mM^- 1 and an estimated detection limit of 0.64 mM, without measurable spectral shift. Selectivity and Fourier transform infrared (FTIR) analyses indicate a preferential surface-mediated response toward urea through weak non-covalent interactions. This work establishes a reproducible strategy for defect-controlled aqueous CIS QDs and supports their use in surface-sensitive PL modulation studies.