Synthesis of lanthanide-doped NaYF4@TiO2 core–shell composites with highly crystalline and tunable TiO2 shells under mild conditions and their upconversion-based photocatalysis

NaYF4:Yb,Tm@TiO₂ core-shell composites were synthesized via a facile hydrothermal method. The highly crystalline TiO₂ shell can be uniformly coated onto lanthanide-doped NaYF₄ microrods and nanorods under mild conditions without calcination. The thickness of the TiO₂ shell can be tuned by varying the ratio of fluoride rods and Ti precursors. The microcomposite with a moderate TiO₂ shell shows excellent photocatalytic activity under near-infrared irradiation.