**4. Conclusions**

ZnO nanorods arrays with high surface area and well-aligned crystallographic orientation were produced via hydrothermal method. The annealed arrays exhibit a crystallite size of 45 nm with (002) preferred orientation and a relatively low lattice strain. Upon argon/SF6 plasma treatment for up to 20 min, the PL intensity in the orange/red region of ZnO is enhanced by 2-fold compared to the ZnO sample without plasma treatment. Moreover, the PL intensity in the blue spectral regime is almost suppressed due to increased defect density. For 5 min Ar/SF6 plasma treatment, the PL broad band intensity maximizes due to maximum oxygen content at the film surface. This finding implies presence of hydroxyl group at the surface, more oxygen in the ZnO lattice (*OL*), fluorine incorporation in terms of F–Zn and F–OH bonds, and passivation of the surface states as well as bulk defects. These findings have implications for fundamental studies and industrial application of the plasma modified ZnO nanostructures in optoelectronic applications including visible light emitting devices and display systems.

**Author Contributions:** A.A. and J.-J.P. designed the scheme of experiments; A.A., I.A., S.V. and K.S. performed the experimental work; M.I., J.-J.P. and G.D. carried out the data analysis; M.A.A. and S.V. accomplished data validation; M.I., A.A. and J.-J.P. prepared the original draft; G.D., M.A.A., I.A., S.V. and K.S. did the necessary writing review and editing; J.-J.P. and M.I. administered the project and acquired funding for this research.

**Funding:** The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding of this research through the Research Group Project no. RGP-283. The authors also express their gratitude to Wallonia Region for financial support (Project Cleanair; convention 1510618, compl. Feder films).

**Conflicts of Interest:** The authors declare no conflict of interest.
