Defect-Related Optical Behavior in Surface Modified TiO₂ Nanostructures

Graphical Abstract

The surface modification of TiO₂ nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Freshly prepared samples exhibited a strong emission near 560 nm (see Figure) (2.21 eV), which red shifts to 660 nm (1.88 eV) and drops in intensity after atmospheric exposure. Electron spin resonance studies identified a resonance at g = 2.0035, which increased significantly with nitridation.

Abstract

The surface modification of TiO₂ nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Anatase TiO₂ structures in the 5–20 nm range, formed by a wet chemical technique, were surface modified and the nitridation of the highly reactive TiO₂ nanocolloid surface, as determined by X-ray photoelectron spectroscopy (XPS) studies, is achieved by a quick and simple treatment in alkyl ammonium compounds. The nitriding process was also simultaneously accompanied by metal seeding resulting in a metal coating layer on the TiO₂ structures. The structure of the resultant titanium oxynitride nanostructures remains anatase. These freshly prepared samples exhibited a strong emission near 560 nm (2.21 eV), which red-shifted to 660 nm (1.88 eV) and dropped in intensity with aging in the atmosphere. This behavior was also evident in some of the combined nitrogen doped and metal seeded TiO₂ nanocolloids. Electron spin resonance (ESR) performed on these samples identified a resonance at g = 2.0035, which increased significantly with nitridation. The resonance is attributed to an oxygen hole center created near the surface of the nanocolloid, which correlates well with the observed optical activity.