Tuning Photoluminescence and Magnetic Properties of Ag–Ga–S and Zn–Ag–Ga–S Quantum Dots via Mn<sup>2+</sup> Doping

Transition metal-doped colloidal quantum dots (QDs) are promising candidates for dualmode imaging due to their tunable optical properties and potential magnetic functionalities.Here, we report the synthesis and characterization of Mn-doped AgGaS (AGS) and ZnSalloyed Ag-Ga-S (AGZS) QDs via a one-pot heating-up method.Upon Mn incorporation, both AGS and AGZS QDs exhibited two distinct photoluminescence (PL) peaks originating from the host QDs and doped Mn ions, with the relative intensities tunable by varying Mn 2+to-total metal cation ratio in the precursor (Mn 2+ /cationpre).The AGZS QDs prepared with Mn 2+ /cationpre ratio of 1.1% exhibited a high PL quantum yield of 45%, with 40% of the emission attributed to the d-d transition of Mn 2+ ions ( 4 T1 6 A1).Time-resolved PL measurements revealed efficient energy transfer from excitons in the host QDs to doped Mn 2+ ions, contributing to enhanced Mn 2+ -related emissions.Surface passivation with a ZnS shell followed by ligand exchange with 3-mercaptopropionic acid allowed stable dispersion of AGZS QDs in aqueous media while retaining optical properties.Since the Mn 2+ -doped QDs also exhibited paramagnetic behavior, we investigated the performance of Mn 2+ -doped AGZS QDs as a contrast agent for magnetic resonance imaging (MRI).The intensity of the T1-weighted MRI signal increased with an increase in the content of doped Mn 2+ .These results demonstrate that Mn 2+ -doped AGZS QDs are promising single-component dual-mode (PL/MRI) nanoprobes for biomedical imaging applications.