Understanding Photoluminescence of Monodispersed Crystalline Anatase TiO2 Nanotube Arrays
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- 作者：Hyunjun Yoo ; Myungjun Kim ; Changdeuck Bae ; Seonhee Lee ; Hyunchul Kim ; Tae Kyu Ahn ; Hyunjung Shin
- 刊名：Journal of Physical Chemistry C
- 出版年：2014
- 出版时间：May 8, 2014
- 年：2014
- 卷：118
- 期：18
- 页码：9726-9732
- 全文大小：473K
- 年卷期：v.118,no.18(May 8, 2014)
- ISSN：1932-7455
文摘
Despite huge potential of nanostructured TiO2 in many applications, the concrete understanding of optical properties associated with their defect structures remains elusive to date. Here, we present a systematic study on the photoluminescence (PL) characteristics of anatase TiO2 nanotube (TNT) arrays as a function of wall thicknesses (twall) and thereby grain sizes. Highly uniform anatase TNTs were prepared by template-directed atomic layer deposition techniques, followed by thermal annealing. The relative amounts of surface/grain boundary (GB) defects to the bulk oxygen vacancies were tailored in a controlled manner by utilizing the crystallization kinetics between thin and thick wall layers during amorphous to anatase transformation. PL spectra of anatase TNT arrays were attained at variable temperatures from 300 down to 20 K. By changing twall, remarkably, the predominant PL emissions were likely discernible from either self-trapped excitons, oxygen vacancies, or surface/GB defects. Our results indicate that the properties of TNTs are surface-dominated when twall < 3 nm and bulk-dominated when twall > 3 nm by detecting surface-dangling bonds of TNTs located as deep traps with decreasing twall. Moreover, our TNT arrays with twall = 20 nm and highly crystalline anatase domains emit resonant PL that may suggest STEs coupled with a specific phonon mode. The present work provides us an emergent understanding on the optical properties of one-dimensional, wide-gap oxide semiconductor photoelectrodes in extremely uniform dimensions.