Photoinduced small polarons bound to hydrogen defects in rutile TiO2
AbstractPhotoinduced absorption in rutile TiO2 has been studied by means of Fourier transform infrared spectroscopy. It is shown that near-band-gap illumination results in a charge-state transition of a hydrogen defect with an O–H stretch mode at 3500 cm−1, as evidenced by the appearance of an anticorrelated vibrational mode with a blueshift of ∼1.3cm−1. The charge-state transition is accompanied by a broad near-infrared absorption band with maximum intensity at ∼7000cm−1. Our data on both the photoinduced vibrational mode and the near-infrared absorption can be conclusively explained in the framework of a model of small electron polarons bound to a Ti atom adjacent to the O–H group of the hydrogen defect.