Measurements of the photoelectrochemical properties of nanocrystalline ZnS electrodes doped
with Mn^(2+) are presented and discussed. The observation of both anodic and cathodic photocurrent
is direct evidence for the nanocrystalline nature of the system. In-situ photoluminescence measurements
showed stable Mn^(2+) related photoluminescence over a large potential range. Due to the
unfavourable kinetics of electron and hole transfer across the interface between the nanocrystallites
and solution, it is concluded that recombination accounts for most of the charge carriers generated
by illumination. Breakdown of the ZnS into elementary Zn and S^(2-) in solution was also
observed at negative potential. This breakdown introduces new non-radiative decay paths and is
responsible for the slow luminescence decrease as a function of operating time