Sub-10 nm lanthanide doped BaLuF5 nanocrystals: Shape controllable synthesis, tunable multicolor emission and enhanced near-infrared upconversion luminescence

• Sub-10 nm cubic phase BaLuF5 nanocrystals were synthesized by a hydrothermal method for the first time.
• Tunable multicolor from yellow to yellow-green was achieved by controlling Gd3+ content in BaLuF5:Yb/Er system.
• Intense near-infrared upconversion luminescence in BaLuF5:Gd/Yb/Tm nanocrystal.
• The enhancement near-infrared luminescence can be realized by adjusting the content of Gd3+ in BaLuF5:Gd/Yb/Tm system.

In this study, sub-10 nm BaLuF5 nanocrystals with cubic phase structure were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared BaLuF5 nanocrystals were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and analyzed by the upconversion (UC) spectra. The TEM results reveal that these samples present high uniformity. Compared with Gd-free samples, the size of BaLuF5:Yb/Er doped with 10% Gd3+ decreased to 5.6 nm. In addition, BaLuF5:Yb/Tm/Gd upconversion nanoparticles (UCNPs) presented efficient near-infrared (NIR)-NIR UC luminescence. Therefore, it is expected that these ultra-small BaLuF5 nanocrystals with well-controlled shape, size, and UC emission have potential applications in biomedical imaging fields.

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