ZnO films were deposited on Si substrates by using DC sputtering and their cathodeluminescence(CL) and photoluminescence(PL) properties at room temperature were investigated. The CL spectra of the ZnO films include three peaks.They are purple(center wavelength about 390nm)

blue(430～450nm)

and green(522～525nm) emissions.These spectra are dependent on the crystal quality of ZnO films.The purple peak appears only in the sample whose crystal quality is good.We also observed that the intensities of purple

blue and green emissions vary with CL electron beam current density.With the increase of electron beam current density

the intensity of blue peak increases almost linearly and the intensity of purple peak increases super-linearly.According to these phenomena

it is deduced that the green emission results from the electron transition between a donor level caused by oxygen vacancies and an acceptor level caused by zinc vacancies.The blue emission includes two transitions of electrons : from the donor to the valence band and from the conduction band to the acceptor.The ultraviolet band would be the excition transition from the band edge emission.At the same time

the wavelength of purple peak exhibits red shift with increasing the CL electron beam current density.We suggest that the increasing carrier density generated by increasing exciting power cause the luminescence center to tend to gap tail levels. Except green

blue and purple peaks

a new ultraviolet peak (334nm) appears in the PL spectra of the ZnO films.The photon energy (3 72eV) of the ultraviolet peak is much larger than the band gap of ZnO.The reason needs to be investigated in further experiments.