Zinc oxide (ZnO) has attracted interest owing to its potential applications including nonlinear optical devices

blue-violet light emission devices

buffer layer for GaN-based devices

visible range transparent electrode for solar cell

display and surface acoustic wave devices.Inspired by the application of ZnO

numerous studies have appeared on the luminescence of ZnO.Two emission bands are usually found.One is a narrow UV emission band and the other is a broad visible emission band at approximately 520 nm.The UV emission from ZnO is commonly attributed to band-to-band or near band edge emission.The nature of the visible emission has been the subject of much research

however

the mechanism behind the visible luminescence has been very difficult to establish.During the past years

oxygen vacancies have been assumed to be the most likely candidates for the recombination centers involved in the visible luminescence of ZnO.Recently

Van Dijken et al.proposed a model for the kinetic mechanism behind the visible emission of nanocrystalline ZnO particles;the visible emission of ZnO was a recombination of a shallowly trapped electron with a deeply trapped hole and the surface state plays an important role during the recombination process.To study the effect of surface defects on luminescence we used polyethylene oxide (PEO) as capping polymer molecules to achieve the surface-modified ZnO nanoparticles.ZnO nanoparticles surface modified by polyethylene oxide(PEO)were fabricated and the influence of surface-modification on optical properties of ZnO were studied.The PL spectra showed two emission bands:one was UV emission

the other was deep level emission related to oxygen vacancies.When the PEO content increased

the ratio of the UV emission to the deep level emission increased.When the PEO content was the largest

the ratio is 31.5

which is much bigger than that of the pure ZnO nanoparticles.So when ZnO nanoparticles were modified by PEO

the UV emission efficiency was enhanced and the quality of the ZnO nanofilm was improved.