Abstract：Phosphorescence sensing technology has attracted much attention in recent years due to its long life, wider gap between the excitation spectrum and emission spectrum, and the ability to effectively avoid interference from the system and light scattering. This study synthesized water-soluble Mn-doped ZnS quantum dots in a reactor using the hydrothermal method. When synthesized quantum dots were characterized，it can be concluded from the XRD results, TEM image, and TEM-mapping image that Mn2+ was successfully doped into the ZnS lattice. The quantum dots exhibited an obvious phosphorescence emission peak at 580 nm, much higher than fluorescence peak at 420 nm. The phosphorescence properties of the quantum dots under different reaction conditions were also investigated. It was found that the characteristic peak of the quantum dots was the highest when the pH of the precursor solution was 11, the reaction time was 30 minutes, and the Mn doping ratio was 4%. Compared with the traditional preparation method, the hydrothermal method in the reactor can effectively dope Mn into the interior of ZnS quantum dots rather than the surface, leading to phosphorescence emission, which is conducive to improving the selectivity and sensitivity of the sensing system. In addition, this study also found that Pb2+ can selectively quench the phosphorescence of Mn-doped ZnS quantum dots, and investigated the effects of buffer pH and reaction time. Under the optimal conditions, a highly sensitive phosphorescence sensing system for identifying Pb2+ ions was established with a linear range of 0.02～20 μmol·L-1, and the detection limit was as low as 6.6 nmol·L-1. At the same time, other metal ions had no obvious interference with this sensing technology. The determination of Pb2+ in water samples from a lake was successfully tested, the recovery rate ranged from 91.9%~114.1%, and the accuracy rate was between 83.0%~109.8%, which proved that this sensitive phosphorescence sensing system had good stability and repeatability.
