Role of Magnetic Coupling in Photoluminescence Kinetics of Mn 2+ -Doped ZnS Nanoplatelets.

Mn 2+ -doped semiconductor nanocrystals with tuned location and concentration of Mn 2+ ions can yield diverse coupling regimes, which can highly influence their optical properties such as emission wavelength and photoluminescence (PL) lifetime. However, investigation on the relationship between the Mn 2+ concentration and the optical properties is still challenging because of the complex interactions of Mn 2+ ions and the host and between the Mn 2+ ions. Here, atomically flat ZnS nanoplatelets (NPLs) with uniform thickness were chosen as matrixes for Mn 2+ doping. Using time-resolved (TR) PL spectroscopy and density functional theory (DFT) calculations, a connection between coupling and PL kinetics of Mn 2+ ions was established. Moreover, it is found that the Mn 2+ ions residing on the surface of a nanostructure produce emissive states and interfere with the change of properties by Mn 2+ -Mn 2+ coupling. In a configuration with suppressed surface contribution to the optical response, we show the underlying physical reasons for double and triple exponential decay by DFT methods. We believe that the presented doping strategy and simulation methodology of the Mn 2+ -doped ZnS (ZnS:Mn) system is a universal platform to study dopant location- and concentration-dependent properties also in other semiconductors.