Sr2BiF7: A New Bismuth-Based Host Material for Lanthanide Ions Doping: Synthesis, Downshifting, and Upconversion Luminescence Properties for Multimode Anticounterfeiting

doped nanomaterials show blue, magenta, and orange-red colors under 365, 395, and 980 nm light, respectively. These results establish that this material can be effectively used as a multimode photoluminescent covert tag to combat counterfeiting.