Trap states and carrier dynamics of TiO2 studied by photoluminescence spectroscopy under weak excitation condition

• Published in: Physical chemistry chemical physics : PCCP Vol. 12; no. 26; pp. 783 - 79
• Main Authors: Wang, Xiuli, Feng, Zhaochi, Shi, Jianying, Jia, Guoqing, Shen, Shuai, Zhou, Jun, Li, Can
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2010
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Binary compound; Oxygen; Recombination; Anatase; Vacancy; Rutile; Donor site; Photocatalysis; Transition element compounds; Luminescence; Photoluminescence; Trap; Lifetime; Trapping; Dynamics; Hydroxyl group; Excitation; Titanium oxide; Power law; Electrons
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/b925277k

Anatase and rutile TiO 2 were investigated with photoluminescence techniques under the weak excitation condition, where trap states play a vital role in carrier dynamics. The visible emission of anatase and near-infrared (NIR) emission of rutile both exhibit extremely long lifetimes up to milliseconds. The decay processes can be well described by the power-law decay which corresponds to the trapping-detrapping effect. These results indicate that the luminescence processes in both anatase and rutile TiO 2 have a close relationship with trap states. The visible emission band was assigned to the donor-acceptor recombination. Oxygen vacancies and hydroxyl groups mainly serve as the donor and acceptor sites, respectively. The NIR luminescence is originated from the recombination of trapped electrons with free holes, while the trapped electrons were formed through two paths, direct trapping or trap-to-trap hopping. The trap states in anatase and rutile TiO 2 may largely influence the photocatalysis process of TiO 2 and determine the photocatalytic activity under stationary illumination. Weak excitation condition is successfully used to study trap states and their effect on carrier dynamics of TiO 2 materials.