  Mn2+-doped semiconductor nanocrystals with tuned location and concentration
of Mn2+ 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 Mn2+
concentration and the optical properties is still challenging because of the
complex interactions of Mn2+ ions and the host and between the Mn2+ ions. Here,
atomically flat ZnS nanoplatelets (NPLs) with uniform thickness were chosen as
matrixes for Mn2+ doping. Using time-resolved (TR) PL spectroscopy and density
functional theory (DFT) calculations, a connection between coupling and PL
kinetics of Mn2+ ions was established.
  Moreover, it was found that the Mn2+ ions residing on the surface of a
nanostructure produce emissive states and interfere with the change of
properties by Mn2+/Mn2+ 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 Mn2+-doped ZnS system is a universal platform
to study dopant location- and concentration-dependent properties also in other
semiconductors.
