Effect of graphene oxide coatings on the optical properties of pulsed laser deposited ZnO:Zn thin films

Highly c-axis orientated ZnO:Zn thin films were successfully prepared by pulsed laser deposition and coated with graphene oxide (GO) using nebulizer spray coating. The structural, morphological, and optical properties of the films were studied before and after annealing under different conditions to produce reduced GO (rGO). Following deposition on the surface of the ZnO:Zn films, the GO sheets showed non-uniform and defective textures. Heavily crumbled sheets were observed for rGO annealed in Ar, while wrinkled sheets were observed for rGO annealed in Ar/H2. The uncoated ZnO:Zn exhibited ultraviolet emission at ∼390 nm attributed to the recombination of excitons and a broad band in the range 400–600 nm centred at ∼450 nm attributed to zinc interstitials. The blue emission at ∼450 nm of ZnO:Zn was enhanced after coating with GO and/or rGO, which was attributed to the coupling of the light-emitting centres with localized surface plasmon resonances from the GO/rGO sheets. However, it was found that annealing of uncoated films also improved their luminescence intensity. These results showed that rGO/ZnO films may be useful for some optoelectronic or photoluminescence applications requiring ultraviolet and blue/green light.