Controllable Multicolor Upconversion Luminescence by Tuning the NaF Dosage

Multicolor upconversion (UC) luminescence of NaYF₄:Yb³⁺/Er³⁺ nanoparticles (NPs) was successfully tuned by simply controlling the NaF dosage. Unlike UC nanocrystals previously reported in the literature with multicolor emission obtained by varying the rare‐earth dopants, the current work developed a new approach to tune the UC emission color by controlling the NaF concentration without changing the ratio and dosage of rare‐earth ions. TEM and powder XRD were used to characterize the shape, size, and composition of the UC luminescent nanocrystals. The luminescence images, emission spectra, and multicolor emission mechanism of the NPs have also been demonstrated. As a result of the excellent ability of this new method to manipulate color emission, this will open up new avenues in the areas of bioprobes, light‐emitting devices, color displays, lasers, and so forth. To demonstrate their biological applications, the water‐stable, biocompatible, and bioconjugatable NaYF₄:Yb³⁺/Er³⁺@poly(acrylic acid) NPs were synthesized by this developed strategy and applied in targeted‐cell UC luminescence imaging.