only has posed a serious threat to enterprises, governments as well as consumers, but also has caused immeasurable economic losses to society. [1,2] In order to protect the legitimate rights and interests of consumers and companies, governments and companies have spent huge sums of capital to develop various anticounterfeiting technologies to increase the recognizability and difficulty of replicating authentic products in response to endless counterfeiting methods. [3][4][5][6] Recently, several well-known types of anticounterfeiting methods, including watermarking technology, [7,8] laser holographic technology, [9,10] barcode technology, [11] and fluorescent anticounterfeiting technology [12,13] have been developed. Among them, fluorescent anticounterfeiting technology has attracted wide attention because of its high-efficiency, easy-toimplement, difficult-to-replicate, high concealment, low-cost, and large-scale preparation characteristics. [14] Currently reported fluorescent materials used in the field of anticounterfeiting mainly include carbon-based quantum dots (QDs), [15][16][17][18] silicon-based QDs, [19][20][21][22] perovskite quantum dots (PeQDs), [23][24][25][26][27] conjugated polymers, [28] rare earth luminescent materials, [1,[29][30][31][32][33] etc.Lanthanide ion (Ln 3+ )-doped upconversion nanoparticles (UCNPs) can emit high-energy UV-visible photons when excited by low-energy near-infrared (NIR) photons with excellent properties, such as narrow-band emission, long fluorescence lifetime, large anti-Stokes shifts, superior light and chemical stability, excellent detection sensitivity, and low biological toxicity, [34][35][36][37] which make them promising candidates for fluorescent anticounterfeiting materials. Generally, the UCNPs doped by Ln 3+ (Ln = Er, Tm, or Ho) ions could be classified into singlemodal luminescent materials for anticounterfeiting. However, the traditional single fluorescence mode and detection light source make this type of anticounterfeit luminescent materials still face the risk of being imitated by counterfeiting. [30,38] Thus, dual-modal fluorescent materials that combine upconversion luminescence (UCL) and down-conversion luminescence (DCL) mechanisms at the same time could greatly increase the difficulty of counterfeiting and are of great significance in the field of anticounterfeiting. As known, CsPbX 3 PeQDs (X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) have 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 ...
