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.