Influence of ultraviolet irradiation on physical properties of nano-NiO films for optical applications

NiO nanoparticles (NPs) were prepared by microwave irradiation technique. The resulted NiO NPs were affirmed during chemical precipitation by thermal analysis and X-ray diffraction (XRD) characterization. XRD showed five distinguishable peaks of NiO. The nano-NiO films were fabricated by drop solution, while the films were irradiated by UV light at different exposure periods of 0, 1, 3, and 5 h. The crystalline size of nano-NiO films was decreased from 27 to 16 nm by UV irradiation process. On the other hand, the conductivity of nano-NiO films has been observed to be increased under the effect of UV irradiation. Also, the optical constants were calculated in the range of 300–2500 nm. The mechanism of the electronic transition of the present sample was characterized by the direct allowed transition, whereas the band energy gap of the as-deposited was evaluated to be 3.81 eV and declined to 2.93 eV for the UV-irradiated film exposed to the UV rays for 5 h. However, the calculated non-linear optical parameters have been found to increase as the irradiation time exposure increases.