|Title:||Rare earth-doped perovskite-structured oxides with strong elastico-mechanoluminescence|
|Advisors:||Kwok, K. W. (AP)|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||107 pages : color illustrations|
|Abstract:||Mechanoluminescence (ML), which refers to the luminescence triggered by an external mechanical load, has been investigated by many scholars since 19th century. The application of ML materials was limited until the research of non-destructive ML induced by elastic deformation was started. Different types of materials have been found exhibiting ML response. However, only a few of them can be practically used in applications. ML materials are generally used as stress sensors in applications and some of them are for dynamic pressure mapping. The working principle of ML, which is related to the release of trapped charge carriers, is still unsolved. Many models have been proposed to explain the observations for specific type of ML materials, but the availability of those theories to other ML materials is still controversial. This is the most significant obstacle for the ML research for the research of new ML materials and new applications. To date, most of the well-developed ML materials can yield greenish-blue (ZnS: Cu+, SrAl2O4: Eu2+) to yellow (ZnS: Mn2+) emissions under applied stress. Therefore, for developing a complete display system, ML materials with the capability of emitting red light are highly desirable. In this work, we report the development of a new ML material, i. e., Ba0.15Ca0.85Ti0.9Zr0.1O3: 0.2Pr3+ (abbreviated as CBTZ-Pr) that possesses a perovskite structure and exhibits strong red emissions under applied stress. Like the other typical ML emissions, the red emission decays with each application of mechanical load. However, it can be recovered after a short-period irradiation with UV light since the elastic deformation would not remain any permanent destruction to the material and is thus called elastic-mechanoluminescence (EML). In this work, the EML responses of CBTZ-Pr is investigated via the application of a tensile stress and the light emission phenomenon is photographed and its intensity is measured. The strong red emission, with its intensity peaked at 611nm, can easily observed by naked eye and captured by photos. The perovskite-structure CBTZ-Pr oxide shows a naturally originated diphase structure, containing two regions or phases of different chemical compositions separated by a clear boundary. The thermoluminescence behavior of the oxide is also examined for investigating the charge trapping centers, in particular their relative depth in the energy band structure. Based on those results, an electron-tunneling model is proposed to elucidate the mechanism of the observed EML phenomenon. Our findings in this work, in particular the proposed mechanism, provide essential information and knowledge for the further development of a new ML material system based on perovskite-structure BaxCa1-xTiyZr1-yO3 oxides.|
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