A general, efficient method of incorporation of metal ions into ultrathin TiO₂ films

A general, efficient method was developed to incorporate a variety of second metal ions into ultrathin TiO₂ films. The thin films were first prepared by the surface sol-gel process from a mixture of the matrix-forming titanium alkoxide and template magnesium alkoxide. Mg²⁺ ion was removed by acid/base treatment, forming highly efficient and robust ion-exchange sites. A large variety of metal ions, including alkaline, alkaline earth, transition, and rare earth elements, were then incorporated into the thin films by ion exchange with Na⁺. The amount of incorporation increased with increasing charge of the metal ions. The rate of the ion-exchange process was investigated in the case of Gd3+. The incorporated metal ions were immobilized by thermal treatment at 450°C. The UV absorption edge of the TiO₂ film was extended to the visible region by Fe³⁺ doping and calcination.