Enhancing upconversion emissions of Er3+/Tm3+/Yb3+ tridoped (NaY(WO4)2/YF3) through TiO2 coating and Bi3+ doping and its photocatalytic applications

Enhanced upconversion property is important for the improvement of photocatalytic activity in the TiO2 based near-infrared (NIR) photocatalysts. Herein, an excellent NIR photocatalyst of Er3+/Tm3+/Yb3+/Bi3+ doped (NaY(WO4)(2)/TiO2/YF3) (ETYB-NTY) was synthesized with a multi-stage upconversion nanocrystal formation process. It is found that TiO2 coatings not only provide photocatalytic activity, but also improve the upconversion emission intensity, which is further enhanced greatly by the doped Bi3+ ions. Under NIR irradiations, ETYB-NTY possesses better photocatalytic activities compared to Er3+/Tm3+/Yb3+ doped (NaY(WO4)(2)/TiO2/YF3) and Er3+/Tm3+/Yb3+ doped (NaY(WO4)(2)/TiO2), since more (OH)-O-center dot and O-2(center dot-) radicals can be produced by the much stronger UV (364 and 380 nm) and violet (409 nm) upconversion emissions in ETYB-NTY. There are also clear improvements for ETYB-NTY in degradation of methyl orange, salicylic acid, and the leachate from incineration plant under UV-vis-NIR irradiation. ETYB-NTY is a novel NIR photo catalyst with special structure and enhanced upconversion property, which has promising applications in organic pollution treatment and solar energy utilization. (C) 2014 Elsevier B.V. All rights reserved.