  Pulsed ArF laser annealing in air and in hydrogen atmosphere improves the
optical properties of ZnO nanostructured films. Independently on the ambient
atmosphere, laser annealing produces two major effects on the photoluminescence
(PL) spectra: first, the efficiency of the exciton PL increases due to decrease
of the number of non-radiative recombination centers; second, the intensity of
the defect-related orange band decreases because of the removing of excessive
oxygen trapped into the films during deposition. However, annealing in the
ambient air also increases the intensity of the green band related to oxygen
vacancies. We show that the combination of laser annealing and passivation of
oxygen vacancies by hydrogen results in films free of defect-related emission
and keeps intact their nanostructural character.
