Photocatalytic Reaction Properties of TiO2-Supported on the Long Lasting Phosphor: Sr4Al14O25:Eu2+,Dy3.

ABSTRACT

The TiO2/Sr4Al14O25Eu2+,Dy3+ 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 (C6H6) gas under UV, visible light illumination, and in the darkness. The photocatalytic composite of TiO2-deposited Sr4Al14O25Eu2+,Dy3+ 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/Sr4Al14O25Eu2+,Dy3+, 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 Sr4Al14O25Eu2+,Dy3+. 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 Sr4Al14O25Eu2+,Dy3+ long lasting phosphor was analyzed by a XRD (X-ray diffraction), TEM (transmission electron microscopy), UV/visible spectroscopy and AES.