Tunable photoluminescence in stoichiometric tetragonal AgInS2 quantum dots: effect of sulfur injection temperature

Achieving high photoluminescence quantum yield (PLQY) in stoichiometric, heavy metal-free AgInS2 quantum dots (QDs) remains a significant challenge, primarily due to the persistent formation of phase impurities during synthesis. In this study, we addressed this limitation by incorporating 1-dodecanethiol (DDT) as a coordinating ligand in both cationic and anionic precursors. This approach allowed for precise control over precursor reactivity, ultimately enabling the synthesis of phase-pure, stoichiometric tetragonal AgInS2 QDs. Systematic variation of sulfur injection temperatures revealed its critical role in tuning QD size (3.2–6.3 nm), optical properties, and defect states. An optimum sulfur injection temperature of 180 °C resulted in a maximum PLQY of 66 %, among the highest reported PLQY for stoichiometric tetragonal AgInS2 QDs synthesized via the hot injection method. The QDs exhibited size-tunable emission across 581.6–745.6 nm and large Stokes shifts of up to 210 nm. Time-resolved photoluminescence and temperature-dependent studies revealed defect-mediated donor–acceptor pair (DAP) recombination dynamics, with average lifetimes reaching 836 ns at optimal synthesis conditions. A size–bandgap relationship was established using both empirical fitting and effective mass approximation (EMA). This work provides new insights into the synthesis of stoichiometric tetragonal AgInS2 QDs and establishes a synthetically accessible, reproducible route towards heavy metal-free QDs for advanced optoelectronic applications.