The precipitation of zinc oxide (ZnO) semiconductor quantum dots was investigated throughout the whole particle formation process, namely reaction, nucleation, growth and ripening and described by means of population balance equations (PBE). Regarding nucleation, the simulation revealed that the mechanism for the solid formation is by orders of magnitude lower than predicted by classical homogeneous nucleation theory. Thus, the earliest stages of particle formation were described by a combination of reaction kinetics determined by experiments for the formation of preformed clusters and subsequent oriented cluster aggregation. Finally, slow Ostwald ripening, i.e. the growth of larger structures at the expense of smaller particles, was modeled in good agreement with the already experimentally determined particle sizes for ripening temperatures between 10 and 50 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.