Enhanced photoluminescence in electrodeposited NiO nanowalls mediated by plasmonic Au nanoparticle

A comparative photoluminescence (PL) study of NiO nanowalls electrochemically deposited on indium-tin-oxide (ITO)- and gold (Au)-coated glass substrates was demonstrated. The NiO nanowalls had with an average diameter of 2–5 μm and a thickness of 50 nm. For Au-coated substrates, the nanowalls were observed to be decorated by spherical Au nanoparticles (NPs), whereas no NP was found for ITO-coated substrates. The X-ray diffraction (XRD) patterns revealed a dominant growth of NiO along (200) direction. For both the substrates, the X-ray photoelectron spectra (XPS) confirmed elemental purity of NiO with an oxidation state of +2. After eliminating the substrate effect, the nanowalls grown on Au-coated substrates revealed prominent XPS peaks related to metallic Au. Room temperature PL spectra for Au-decorated sample showed a remarkably intense peak at 544 nm corresponding to green light. The peak intensity was observed to be 30 times higher for Au-coated substrates with a wide red-shift. This optical enhancement was attributed to the far-field and near-field radiative effects caused by plasmonic resonance of Au NPs in the vicinity of high-k dielectric NiO nanowalls.