"The optical properties of ZnO thin film have been studied using photolurninescence(PL) spectroscopy with the change of sample temperatures from 10 K to 290 K. The spectrum at 10 K showed the characteristic emission lines of ZnO which were as follows: free exciton(FX) at 3.369 eV, neutral donor-bound exciton(D^0X) at 3.360 eV, two electron satellite(TES) at 3.332 eV, D^0X-1LO at 3.289 eV, and donor-acceptor pair(DAP} transiton at 3.217 eV. From the spectral evolution with temperatures, two features could be identified as temperature went higher: (1) the bound excitons changed gradually into free excitons, (2) DAP turned into free electron-acceptor transition(e.A^0). The PL intensity of free exciton increased with the increase of temperatures, which was accompanied by the decrease of the intensity of bound excitions and bound excition-related transitons such as TES and D^0X-1LO. At 80 K DAP transition disappeared, while (e.A^0) transition started to appear at 30 K."
