Photocatalytic Reaction Properties of TiO₂-Supported on the Long Lasting Phosphor: Sr₄Al 14 O 25 :Eu 2+ ,Dy 3 .

The TiO₂/Sr4Al ₁₄ O25:Eu ²⁺ ,Dy ³⁺ photocatalytic composite was prepared by depositing the nano-crystalline titanium dioxide layer on the long-lasting phosphor substrate of strontium aluminate, using a low-pressure chemical vapor deposition (LP-CVD). The photocatalysis characteristic was studied by examining the photodegradation of benzene (C ₆ H ₆ ) gas under UV, visible light illumination, and in the darkness. The photocatalytic composite of TiO₂-deposited Sr₄Al ₁₄ O ₂₅ :Eu ²⁺ ,Dy ³⁺ showed an active photocatalytic reactivity under UV-light as well as visible-light illumination. The mechanism of the photocatalysis reaction for the TiO₂-deposited strontium aluminate phosphor composite was interpreted in point of the energy band structure and phosphorescent emission. The coupling of nanocrystalline TiO₂ with the strontium aluminate phosphor might result in an energy band bending at the interface of TiO₂/Sr₄Al ₁₄ O ₂₅ :Eu ²⁺ ,Dy ³⁺ , making the titanium dioxide at the junction to be photo-reactive even in a visible wavelength region. In addition, the depth profile of Auger electron spectroscopy (AES) confirmed a possible formation of oxygen vacancies at the interface between TiO₂ and Sr₄Al ₁₄ O ₂₅ :Eu ²⁺ ,Dy ³⁺ . Then, oxygen defects create extra electrons which may excited subsequently to the conduction band and participate in a photocatalytic reaction, resulting in an enhancement of the photodecomposition of benzene. The LP-CVD TiO₂-strontium aluminate phosphor was also photoactive in the darkness because of light emission from the long lasting phosphor. Also, the TiO₂-deposited Sr₄Al ₁₄ O ₂₅ :Eu ²⁺ ,Dy ³⁺ long lasting phosphor was analyzed by a XRD (X-ray diffraction), TEM (transmission electron microscopy), UV/visible spectroscopy and AES.