Photocatalytic characteristics for the nanocrystalline TiO₂ supported on Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor beads

The photocatalytic behaviors of TiO₂-supported on the long lasting phosphor beads were examined. Nanocrystalline TiO₂ was coated on ellipsoidal-spherical beads of an alkaline earth aluminate phosphor, Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺, by low pressure chemical vapor deposition (LPCVD). The photocatalytic reaction was examined by measuring the decomposition of benzene and toluene gases 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 mechanisms of the photocatalytic reactivity for the TiO₂-coated Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor beads were discussed in terms of the crystal structure at the interface, energy band structure and phosphorescence. The coupling of TiO₂ with the Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor resulted in energy band bending in the junction region between TiO₂ and Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor, which makes the TiO₂ crystal at the interface photo-reactive under visible light irradiation. The LPCVD TiO₂-coated Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor beads were also photo-reactive in the dark through the light photons emitted from the Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor.