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

Achieving high photoluminescence quantum yield (PLQY) in stoichiometric, heavy metal-free AgInS 2 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 AgInS 2 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 AgInS 2 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 AgInS 2 QDs and establishes a synthetically accessible, reproducible route towards heavy metal-free QDs for advanced optoelectronic applications.