Kinetic model for color-center formation in TiO₂ film using femtosecond laser irradiation

The authors investigate the formation of color centers (CC) using a femtosecond laser, which causes the darkening of TiO₂ film surfaces and reduction of their electrical resistance under visible-light illumination. They propose a kinetic model to explain the CC formation from femtosecond laser irradiation. The kinetic model treats three components, which are conduction-band electrons, self-trapped excitons or polarons, and color centers. The CC formation coefficient is assumed to be expressed by the Arrhenius equation. The laser fluence dependence on the decrease of the electrical resistance is well explained by the kinetic model.