Abstarct: Excitons are bound electron-hole pairs that are formed when light is absorbed in certain materials (so-called excitonic materials, such as inorganic and organic molecular semiconductors, quantum dots films, carbon nanotubes, and polymers semiconductors). Excitonic materials have a wide variety of optoelectronic applications such as light-emitting diodes, solar cells, photodetectors, and lasers. Among these, colloidal quantum dot films that are synthesized by bonding quantum dots together with the help of organic ligands, are of great importance. CdSe/CdS core/shell colloidal thin film is a typical example of these structures. Excitons that are generated upon light absorption in a colloidal quantum dot (QD) film are spatially localized and can move during their lifetime between the adjacent QDs via the incoherent diffusion mechanism. However, because of the inhomogeneity in the size distribution of the QDs and size of the ligands that connect the QDs, the diffusion coefficient is not constant and shows a time-dependency that in turn is determined by the Forster radius. In this dissertation, by solving the continuity equation for the excitons, we present a model that can describe the time evolution of the exciton population in a disordered colloidal QD system. The results of the modeling are compared to the experimental data reported for the transient photoluminescence behavior of the CdS/CdSe core-shell solid films. The results show that a unique Forester radius cannot be assigned to the colloidal films. Considering the distribution of populations with different Forester radii, good agreement between the model and the experimental data is obtained.