We report a simple method for preparing polycrystalline ZnO thin films by thermal oxidation of metallic Zn films

which were prepared by plasma assisted E-beam evaporation.X-ray diffraction (XRD) and photoluminescence (PL) spectra were used to characterize the structural and optical properties of the thin films.XRD indicate that there are ZnO nanoparticles exist in the as-grown Zn film result from O

2

plasma oxidation.With the annealing temperatures increasing

the grain sizes gradually increase and the quality of the hexagonal wurtzite structural ZnO thin films are evolution.The photoluminescence spectra show a strong near band edge (NBE) emissions with a weak deep level (DL) emission.Because of the quantum confinement effect and the dispersion of the grain size

the full width at half maximum (FWHM) of the photoluminescence (PL) peaks for the as-grown film is more wide and the PL peak position is shorter than that of the annealed ZnO films.Among samples of annealed ZnO films

the PL intensity of the bound exciton reduces with the increase of the thermal oxidation temperature

which drive UV PL peaks to shorter wavelength.The dependence of PL spectra on temperature from 82K to 300K for ZnO thin film annealed at 600℃ indicates that the bound exciton emission decrease and PL peaks exhibit red shift with the increase of annealing temperature.Peak position of the free-exciton emission is a function of temperature from 82～220K.The theoretical simulation to the experimental data is obtained by using Eq.:

E

(T)=

E

(0)- α

T

2

/(

T

+β).The consequence of the theoretical fit agrees well with the reported value.