Highly c-axis oriented polycrystalline MgxZn1-xO (x < 0.20) thin films were prepared by chemical spray pyrolysis. It is found that the optical gap energy of the zinc oxide (ZnO) films is affected not only by the Burstein-Moss band-filling effect, but also by the bandgap narrowing effects such as electron-electron and electron-impurity interactions. The influence of the highly introduced donors and free-electrons is also confirmed on photoluminescence spectra of ZnO films via the broadening of the bound exciton line and the appearance of the non-k-conserving band-to-band emission. The MgxZn1-xO (x < 0.20) films exhibited a broad unstructured near-band-edge (NBE) emission shifting continuously towards higher energy side with increasing composition x. The NBE emission is ascribed to radiative transitions from tail states of the conduction band to those of the valence band.