[2010年05月28日]

弱激发条件下氧化钛光生电子和空穴动力学研究

     由于其独特的光学和化学性质,TiO2被广泛应用于光催化、光伏电池等领域。TiO2中的光生电子和空穴除参与光催化反应外,还被缺陷态捕获猝灭、发生电子空穴复合等过程,其中复合过程是决定TiO2光催化性能的一个重要因素。

          光致发光光谱专门研究光生载流子的辐射复合过程,它是表征复合过程的强有力工具之一。由于TiO2发光量子效率低,几乎所有关于TiO2的时间分辨发光研究都使用脉冲激光作为激发光源。瞬态吸收光谱研究表明,TiO2的复合过程对激发光源的强度非常敏感。为了理解灯或太阳光为光源的实际光催化过程,使用光致发光光谱在弱激发条件研究复合过程是非常必要和重要的,这方面工作迄今还未见报道。

     我组使用微秒闪光灯作为光源,在低温条件下使用时间分辨光致发光光谱研究了锐钛矿和金红石TiO2。使用波长依赖时间分辨发光光谱研究了TiO2发光带的发光起源。束缚态的数量和束缚能级深度决定了锐钛矿和金红石TiO2不同的载流子复合过程。根据热处理对载流子动力学的影响讨论了束缚态载流子在光催化过程中的作用。结果表明,弱激发条件下光致发光光谱是一种确定束缚态分布及其对载流子动力学影响的有效技术,这对理解真实光催化过程非常重要。

 

Article

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

Xiuli Wang, Zhaochi Feng, Jianying Shi, Guoqing Jia, Shuai Shen, Jun Zhou and Can Li*

Phys. Chem. Chem. Phys., 2010, DOI: 10.1039/b925277k

http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b925277k

Abstract

Anatase and rutile TiO2 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 trappingdetrapping effect. These results indicate that the luminescence processes in both anatase and rutile TiO2 have a close relationship with trap states. The visible emission band was assigned to the donoracceptor 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 TiO2 may largely influence the photocatalysis process of TiO2 and determine the photocatalytic activity under stationary illumination.

 

Copyright© 2009 Can Li's Group , All Right Reserved