Influence of Mn²⁺ concentration on Mn²⁺-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties

The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn(2+) (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn(2+)-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn(2+) and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions.