Electronic and optical properties of TiO2 and its polymorphs by Z-scan method

• Published in: 中国物理B：英文版 2014-08 (8), p.340-344
• Main Author: S. Divya V P N Nampoori P Radhakrishnan A Mujeeb
• Format: Article
• Language: English
• Subjects: Z扫描; 三阶非线性极化率; 二氧化钛; 光学性质; 多晶型物; 电子结构; 金红石型; 锐钛矿型
• ISSN: 1674-1056; 2058-3834
• DOI: 10.1088/1674-1056/23/8/084203

TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable prop- erties. TiO2 is known to exist in nature in three different crystalline structures： rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol-gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of Z（3） for amorphous, anatase, and rutile are also calculated and found to be 5 × 10^-19 m2/V2, 27 × 10^-19 m2/V2, 19 × 10^-19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.