Optical properties of porous anodic alumina films implanted with ZnO nanoparticles

Abstract

Porous anodic alumina (PAA) films with highly ordered pore arrays were prepared by a two step anodization process in 0.3M oxalic acid solution at 0°C. ZnO nanoparticles were loaded into the nanopores of PAA films by soaking the PAA films in an aqueous solution of zinc acetate and then annealing them at 500°C. The PAA films and ZnO/PAA composites were characterized by scanning electron microscope, X-ray diffraction, ultraviolet-visible spectrophotometer and fluorescent spectrometer. The highly ordered PAA films are amorphous, the PAA films have a high optical transmissivity in visible range and a wide blue photoluminescence band in the wavelength range of 350~550nm. The photoluminescence intensity and peak position depend strongly on the excitation wavelength. ZnO nanoparticles loaded into PAA films display a pure wurtzite ZnO phase, the average diameter of ZnO particles is 10.8nm. The transmissivity of PAA films declines after ZnO is loaded in. The photoluminescence of ZnO/PAA films exhibits intense and broad emission spectra in the wavelength range of 350-600nm. There is only one strong photoluminescence peak at 430nm when excited at 340nm wavelength, the photoluminescence peak divides into two peaks of 410nm and 460nm while excited at 380nm wavelength. The oxygen vacancies, F⁺ centres, are responsible for the photoluminescence of ZnO nanoparticles loaded into PAA films.