White-light emitting ZnO-SiO2 nanocomposite thin films prepared by the target-attached sputtering method

ZnO-SiO2 nanocomposite thin films were prepared using the target-attached RF sputtering method without substrate heating. The PL measurements showed that the SiO2 films containing uniformly dispersed ZnO nanoparticles emit white light consisting of violet, blue, and Green-yellow band emissions. The presence of the blue emission is attributed to the large number of ZnO/SiO2 interfaces, which enlarges the depletion layer width and then enhances the related transition. The Gaussian curve fitting of PL spectra revealed that the competition between the blue and green-yellow band emissions and the relative emission intensity is strongly associated with the number of ZnO nanoparticles embedded in the SiO2 matrix. XPS analysis revealed that the main component of the oxygen defect species in the ZnO nanocomposite thin films is 'O-' ions (531.1-531.7 eV) at the subsurface. Within the knowledge of the defect configuration, XPS data were also utilized to estimate the oxygen vacancies and the specific carrier concentration in ZnO nanoparticles and relate to the integrated intensities of emission bands. Further analyses indicated that the defect structure of samples could be manipulated by the number and distribution of ZnO nanoparticles in SiO2 matrix to yield a distinct luminescence spectrum.