Enhancing upconversion emissions of Er super(3+)/Tm super(3+)/Yb super(3+) tridoped (NaY(WO sub(4)) sub(2)/YF sub(3)) through TiO sub(2) coating and Bi super(3+) doping and its photocatalytic applications

Enhanced upconversion property is important for the improvement of photocatalytic activity in the TiO sub(2) based near-infrared (NIR) photocatalysts. Herein, an excellent NIR photocatalyst of Er super(3+)/Tm super(3+)/Yb super(3+)/Bi super(3+) doped (NaY(WO sub(4)) sub(2)/TiO sub(2)/YF sub(3)) (ETYB-NTY) was synthesized with a multi-stage upconversion nanocrystal formation process. It is found that TiO sub(2) coatings not only provide photocatalytic activity, but also improve the upconversion emission intensity, which is further enhanced greatly by the doped Bi super(3+) ions. Under NIR irradiations, ETYB-NTY possesses better photocatalytic activities compared to Er super(3+)/Tm super(3+)/Yb super(3+) doped (NaY(WO sub(4)) sub(2)/TiO sub(2)/YF sub(3)) and Er super(3+)/Tm super(3+)/Yb super(3+) doped (NaY(WO sub(4)) sub(2)/TiO sub(2)), since more times OH and O sub(2) super( times -) 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 photocatalyst with special structure and enhanced upconversion property, which has promising applications in organic pollution treatment and solar energy utilization.