“…On the contrary, the emission intensities at the blue region of the NaYF 4 :Yb,Tm@TiO 2 are slightly suppressed likely due to the shielding effect of TiO 2 since the energy is insufficient to excite TiO 2 . Ln element–induced upconversion visible–NIR capture has been validated by many reports through the construction of diverse upconversion/semiconductor composites, including a great number of binary NaYF 4 :Yb,Tm@TiO 2 composites with different structures, NaYF 4 :Yb,Tm–BiOCl nanosheets, ZnWO 4 :Er,Tm,Yb–BiOI, NaGdF 4 :Yb,Tm@TiO 2 , NaYF 4 :Yb,Tm@ZnO, BiVO 4 /CaF 2 :Er,Tm,Yb, NaYF 4 :Yb,Er/Au/CdS, NaYF 4 :Yb,Er,Tm@TiO 2 –Au, and so on.…”