Composites of Silver Nanoclusters and Cellulose Nanocrystals with Tunable Emission as Multicolor Inks

Here, we report fluorescent films of silver nano-clusters (AgNCs), polyvinylpyrrolidone (PVP), and photonic cellulose nanocrystals (CNCs) with a tunable fluorescence emission color by an evaporation-induced self-coassembly route. The AgNCx-CNC films with a low AgNC loading display a red structural color, in which the chiral nematic structures of the CNCs are preserved. The typical film of AgNC6-CNCs exhibits a negative circularly polarized luminescence signal because of the photonic band gap effect, and the glum value at 650 nm reaches -0.12. The AgNC-CNC films show promising anticounterfeiting potential for their humidity responsiveness. Additionally, the AgNCs show changes in emission color in response to the pH of the medium, which is attributed to the pH influencing the electron transfer from the ligands to the metal core through Ag-S bonds and the size of AgNCs. Furthermore, the suspension of AgNC-CNCs at different pH values is stable enough, which can be used as a multicolor fluorescent ink to write on paper to obtain photoluminescent patterns with different colors.