Synthesis of the TiO₂-long lasting phosphor (Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺) composite and its photocatalytic reaction properties

This study has investigated on the photocatalytic behavior of the nanocrystalline TiO2 coupled with long lasting phosphorescent materials. Nanocrystalline titanium dioxide layers were directly deposited on the long lasting phosphor plates of strontium aluminates, Sr4Al14O25:Eu2+,Dy3+, by low-pressure chemical vapor deposition (LPCVD). The photocatalytic reaction was examined by measuring the decomposition of benzene gas by gas chromatography under ultraviolet, visible light (λ> 410 nm) irradiation, as well as in the dark. The LPCVD TiO2-coated Sr4Al14O25:Eu2+,Dy3+ showed an active photocatalytic reaction under visible irradiation. The mechanism of the photocatalytic reactivity for the TiO2-coated Sr4Al14O25:Eu2+,Dy3+ phosphor was identified in terms of the energy band structure and phosphorescence. The coupling of TiO2 with the Sr4Al14O25:Eu2+,Dy3+ phosphor might result in energy band bending in the junction region, which makes the TiO2 crystal at the interface photo-reactive under visible light irradiation. The LPCVD TiO2-coated Sr4Al14O25:Eu2+,Dy3+ phosphor was also photo-reactive in the dark through the light photons emitted from the Sr4Al14O25:Eu2+,Dy3+ phosphor. In addition, the TiO2-coated Sr-Al-O long lasting phosphors were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Auger electron microscopy, and fluorescence spectrophotometer.