Enhancing the Photocatalytic Activity of Sr4Al14O25:Eu2+,Dy3+ Persistent Phosphors by Codoping with Bi3+ ions

Abstract

The photocatalytic activity of Bismuth codoped Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a post-annealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase of Sr₄Al₁₄O₂₅: Eu²⁺,Dy³⁺,Bi³⁺ phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micro grains with sizes in the range of 0.5-20 μm. The samples present an intense greenish-blue fluorescence and persistent emissions at 495 nm, attributed to the 5d-4f allowed transitions of Eu²⁺. The fluorescence decreases as Bi concentration increases; that suggest bismuth induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation whereas only 62.49% MB degradation is achieved under UV irradiation. Our Results suggest that codoping the persistent phosphors with Bi³⁺ can be an alternative to enhance their photocatalytic activity.

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