Multicolor Luminescent Anti-Counterfeiting Barcode Based on Transparent Lanthanide-Doped NaYF4/Poly(Vinyl Alcohol) Nanocomposite with Tunable Full-Color Upconversion Emission

In this paper, we report the synthesis of transparent lanthanide-doped NaYF4 phosphors/poly(vinyl alcohol) (UCPs/PVA) nanocomposites with full-color upconversion emission for construction of multicolor luminescent anti-counterfeiting barcode. By deliberate design of water-dispersible lanthanidedoped NaYF4 upconversion phosphors and precise control of the doped lanthanide ions (dopant pairs and molar ratio), three-primary RGB UCPs with fine red, green and blue upconversion emission were synthesized. The as-prepared three-primary RGB UCPs were incorporated into poly(vinyl alcohol) (PVA) matrix at a fixed concentration to balance the transparence and fluorescence intensity of the UCPs/PVA nanocomposite. The combination of emissions from different types of UCPs with selected ratios in PVA matrix was used to prepare UCPs/PVA nanocomposite with various upconversion emissions. It was demonstrated that the separation distance between UCPs was large enough to suppress inter-particle energy transfer, and thus the emissions of each UCPs were well preserved. This facilitated the fabrication of UCPs/PVA nanocomposite with tunable full-color upconversion emission based on the trichromatic additive color theory. The relevance of these multicolor UCPs/PVA nanocomposites to barcode materials and application in anti-counterfeiting field were also confirmed.