Embellishment of Upconversion Nanoparticles with Ultrasmall Perovskite Quantum Dots for Full‐Color Tunable, Dual‐Modal Luminescence Anticounterfeiting

Abstract Advanced fluorescent anticounterfeiting technology has attracted widespread attention and encourages people to develop reliable luminescent materials with multiple colors and tunable luminescence. Here, novel nanocomposites composed of perovskite quantum dots (PeQDs) and upconversion nanoparticles (UCNPs) are successfully designed and served as efficient anticounterfeiting inks. NaYF 4 :Yb/Tm@NaYF 4 :Yb core–shell UCNPs are formed first and then ultrasmall CsPbX 3 (X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) PeQDs linked on the surface of UCNPs by seeded‐growth strategy. UCNPs‐CsPbX 3 nanocomposites can not only provide multicolor downconversion luminescence (DCL) under ultraviolet (UV) excitation, but also produce tunable upconversion luminescence (UCL) under 980 nm continuous‐wave laser excitation. Finally, UCX 3 nanocomposites are mixed with prepolystyrene (PS) and the resulting UCX 3 /PS with excellent water stability and photostability can be employed as multicolor fluorescent ink for both writing and printing. These findings not only present a general method to fabricate novel nanocomposites combining both advantages of UCNPs and PeQDs, but also provide insight for the practical application in the field of anticounterfeiting.