Synthesis and luminescence characteristics of manganese-doped ZnSe quantum dots synthesized in aqueous solution through internal doping

Long-term stable manganese ion-doped ZnSe/ZnS quantum dots were prepared through an internal doping strategy. The internal doping method consisted of nucleation of MnSe core particles, exchange of manganese ions for zinc ions, and formation of an external layer of ZnSe in an aqueous solution. The internally doped Mn:ZnSe showed excellent optical properties compared with those of external doping or interfacial doping; 31% increase in photo-luminescence (PL) intensity. To optimize multiple emission peaks and color purity, varying the Mn/Zn ratio, controlling pH, and multi-step injection of Zn precursor were used. The resulting quantum dots exhibited high color purity of 96% while suppressing trap emission. The highest photo-luminescence was achieved when the molar ratio of Mn to Zn was 0.02. It was also revealed that the presence of the ZnS shell of the Mn2+-doped quantum dots enhanced the long-term stability of the quantum dots up to at least 80 days. This study implies the non-toxic and facile synthesis of Mn:ZnSe quantum dots by internal doping strategy can be an environmentally friendly and highly efficient process of color-controlled ZnSe quantum dots for biomedical imaging applications.