Photo-luminescence from passive oxide films on nickel and chromium by photo-excitation of UV light

Abstract

Photo-luminescence emission was measured from the thin passive oxide film on nickel and chromium under the in-situ condition in 0.1 kmol m −3 (M) sulfuric acid solution at pH 0.9 and neutral buffer solution of borate-boric acid mixture at pH 8.4 in order to obtain the insight of the electronic properties in the passive oxide film as thin as a few nm. The photo-luminescence induced by UV laser beam at 325 nm wavelength from nickel oxidized in both pH 0.9 sulfuric acid and pH 8.4 borate buffer solutions exhibited a broad spectrum feature with a peak at 400–420 nm. The energy of the peak wavelength from 400 to 420 nm is 2.95–3.10 eV which may correspond to the band-gap energy of the semiconduncting NiO. The photo-luminescence spectra from chromium oxidized in the sulfuric acid and neutral borate solutions had a peak at 400 nm and about 440 nm, respectively. These photo-emission from nickel and chromium oxidized is assumed to correspond to luminescence accompanied by recombination between excess electrons produced by UV light illumination in the conduction band and positive holes in the valence band. The broad tailing of the luminescence at longer wavelength side may represent high density of localized states originated in an amorphous nature of the passive oxides.