In the present work, we reported the synthesis of Mn 2+ -doped Zn-In-S quantum dots (QDs) with high optical performance in a controlled manner. The effects of the temperature, the introduced ODE-S amount and Zn/In ratios in the raw materials, as well as the Mn 2+ doping concentrations on the photoluminescence (PL) properties of Mn 2+ -doped Zn-In-S QDs were investigated systematically. The resultant QDs exhibit tunable bandgaps ranged from 2.9 to 3.7 eV, well-resolved Mn 2+ d-d emission with a PL quantum yield (QY) of 56 % and a surprisingly long excited state lifetime up to ~4.2 ms, suggesting their excellent PL properties. Meanwhile, the initial high PL QY of the obtained Mn 2+ -doped Zn-In-S QDs in organics solvent could be preserved very well once they were transferred into aqueous media via ligand exchange. Furthermore, the as-synthesized QDs exhibit an excellent thermal stability up to 200 o C in a crude solution.. desired to develop cadmium-free alloy QDs with tunable bandgaps to meet the versatile applications.As a typical II-III-VI semiconductor, the "green" chalcogenide Zn-In-S materials have been extensively applied in catalysis, charge storage, and thermoelectric energy conversion, due to its high chemical stability and composition tunable optical bandgaps. 23-25 Furthermore, Shen et al pointed out that doping transition metals such as Cu, Mn into ZnIn 2 S 4 host could further improve their photocatalytic activity. 26,27 However, to date, most reported works were mainly focused on the Zn-In-S microcrystalline, suggesting that there remain material-and fabrication-related obstacles to obtain the small and uniform Zn-In-S QDs. 23, 25, 28 Until recently, Peng et al reported the growth of ZnIn 2 S 4 QDs with tunable sizes ranged from 2.1 to 9.2 nm and a high photocatalytic activity. 28 More recently, Zhang et al reported the optical properties of Cu doped Zn-In-S QDs, showing a high PL quantum yield (QY)and a composition-tunable PL emission over the entire visible spectral window and extending to the near-infrared spectral range. 29 However, to the best of our knowledge, little attention has been paid to the Mn 2+ -doped Zn-In-S NCs.Herein, we reported the growth of cadmium-free Mn 2+ -doped Zn-In-S QDs with high PL via a multi-step hot-injection strategy. The influences of various experimental variables on the growth and PL of the QDs, including the nucleation temperatures for the Mn:ZnInS core nanocluster, the amount of octadecene ODE-S, the Zn/In ratios, as well as Mn 2+ dopant concentration-dependent optical properties, 14 PL intensities increase rapidly and approach the highest one at ODE-S of 0.2 mmol, and then reduce with the further increase of ODE-S. In principle, when the S precursor is used in large excess, the cationic precursor should be consumed rapidly, and small-sized stable Mn:ZnInS nanoclusters would be the resultant products. On the other hand, the presence of additional excessive amount of ODE-S may result in the S-rich surface of the obtained Mn 2+ -doped Zn-In-S QDs, which allows the...