Nitrogen doping on NiO by reactive magnetron sputtering: A new pathway to dynamically tune the optical and electrical properties

•Nitrogen doping into NiO lattice (4at.%) is achieved by only monitoring the N2/O2 gas ratio in the plasma.•The replacement of O by N leads to a narrowing of the optical band-gap energy from 3.6 to 2.3eV.•The origin of the narrowing is explained by the presence of an intermediate band and the introduction of occupied N 2p states.•Electrical conductivity of NiO:N samples depends on the amount of nickel vacancies and the nitrogen doping.