In this paper, we report on rf power induced change in the structural and optical properties of nickel oxide (NiO) thin films deposited onto glass substrates by rf magnetron sputtering technique. The crystallinity of the film was found to increase with increasing rf power and the deposited film belong to cubic phase. The maximum optical transmittance of 95% was observed for the film deposited at 100 W. The slight shift in transmission threshold towards higher wavelength region with increasing rf power revealed the systematic reduction in optical energy band gap (3.93 to 3.12 eV) of the films. The dispersion curve of the refractive index shows an anomalous dispersion in the absorption region and a normal dispersion in the transparent region. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion parameters, dielectric constants, relaxation time, and optical non-linear susceptibility were evaluated. We have made an attempt to discuss and correlate these results with the light of possible mechanisms underlying the phenomena.

A nickel oxide (NiO) thin film with better reversibility, high optical modulation, and enhanced coloration efficiency with fast switching time was prepared using radio frequency (rf) magnetron sputtering technique. A cubic phase and spherical shaped crystal grain morphology of the NiO film have been determined from structural and surface morphological studies. A micro-Raman study showed two bands around 570 cm⁻¹ and 1100 cm⁻¹ corresponding to the vibrations of Ni–O. An X-ray photoelectron spectroscopic study confirmed the compositional purity and the presence of Ni²⁺ and Ni³⁺ ions in the film. In addition, the observed transmission threshold at about 368 nm revealed the presence of Ni vacancies or the presence of Ni³⁺ ions along with Ni²⁺ ions in the deposited film. The photoluminescence peak located at 368 nm in the UV region is attributed to band-edge emission, which may be due to the transition of Ni²⁺ ions from the top of the 3d⁸ valence band to the bottom of the 3d⁸ conduction band. The electrochromic studies reveal an excellent performance with a highest coloration efficiency of 235 cm² C⁻¹, reversibility of 64%, optical modulation of 58%, coloration time of 1.2 s and bleaching time of 1.1 s. An electrochemical impedance measurement indicates fast lithium ion transfer with fast switching time, which facilitates the improved electrochromic behavior.