The optical properties of ZnO nanoparticles capped with polyvinyl butyral

ZnO nanoparticles capped with polyvinyl butyral (PVB) have been synthesized by the sol-gel process. Photoluminescence (PL) spectra show a remarkable decrease in visible emission intensity after ZnO nanoparticles are capped with PVB, which indicates that dangling bonds and defect states at the surface of ZnO nanoparticles are markedly passivated. As a result, the process of surface-trapped hole tunneling back into the particles to form V-O** recombination center is blocked. The PL spectra of thin films show a strong ultraviolet (UV) emission with very weak visible emission. The typical intensity ratio of the UV emission at 3.45 eV to the visible emission at about 2.41 eV is 43.3, which shows an obvious improvement in luminescence properties by the surface passivation with PVB. Low-temperature PL spectra of ZnO powder at 93.8 K are dominated by free exciton, bound exciton and the LO-phonon replica of the bound exciton.