| Summary: | 博士 === 國立交通大學 === 材料科學與工程系 === 89 === Titanium oxide thin films were fabricated by the thermal oxidation of sputtered Ti film and wet chemical [sol-gel and metalorganic decomposition (MOD)] processing. The different physical characteristics of TiO2 films such as phase composition, the rate of anatase-to-rutile (A→R) phase transformation, texture, and microstructure was first investigated. For the TiO2 films prepared by the thermal oxidation of Ti film, only single-phase rutile TiO2 was detected and its crystal orientation was strongly related the crystallinity of initial Ti films. On the other hand, the A→R phase transformation can be observed in the TiO2 films fabricated by wet chemical processing. Compared with sol-gel-derived TiO2 film, the MOD-derived TiO2 film had a lower A→R transformation temperature and activation energy, which is attribute to the smaller grain size and more potential nucleation sites existing in the un-transformed MOD-TiO2 film.
The sol-gel method was utilized to fabricate the Er3+-doped TiO2 and SiO2-based materials. Some hetero-species such as Y3+or Yb3+ ions are selected to codope with Er3+ ions into the host materials. It was found that optically active Er ions have Er2O3-like local environment in the Er3+-Y3+ (or Er3+-Yb3+) codoped TiO2 and SiO2 systems. Yb3+ or Y3+ codopant can obviously enhance the ~1.54μm PL intensity and enlarge spectral bandwidth of Er3+-doped TiO2 and SiO2 systems. The average spatial distance between Er3+ ions is enlarged due to the partial substitution of Yb3+ (or Y3+) for Er3+ ions in the Er2O3-like local structure. This indicates that both Yb3+ and Y3+ ions act as dispersers to Er3+ ions and reduce the concentration quenching effect. In addition, Yb3+ ion does not only play a disperser but also sensitizer to Er3+ ion. This dual effects lead to Er3+-Yb3+ codoped TiO2 system to have larger visible and infrared fluorescence efficiencies compared to Er3+-Y3+ codoped TiO2 system.
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