Tridoped Upconversion Nanoparticles with Tuneable Emissions for Anti-Counterfeiting — 101a — Gopala Krishna Murthy Kalapala, Anjaneyulu Putta

Counterfeiting is one of the major menaces affecting the global economy. It has been estimated that sales of counterfeit and pirated goods amount to several trillions a year globally. Various luminescent materials have been used in traditional anti-counterfeiting techniques. However, those luminescent materials lack complex features and are vulnerable to illegal replication. It is thus essential to develop novel anti-counterfeiting luminescent materials with complex multi-level security features. Lanthanide-doped sodium yttrium fluoride (NaYF₄) upconversion nanoparticles (UCNPs) have been explored for information encryption and anti-counterfeiting in the last decade. However, most studies are confined to single or dual-doped UCNPs. There are only a few reports on UCNPs with multiple dopants. Furthermore, there is a lack of sufficient understanding of the interactions among these dopants and their impact on the overall optical performance. Herein, we synthesized NaYF₄: Yb-Er-Tm tridoped UCNPs and studied the effect of Tm doping concentration on the luminescence behavior. When irradiated with a 980 nm laser, the synthesized tridoped UCNPs have green, red, and near-infrared (NIR) emissions. We found that the intensities of red and NIR emissions increase with the increase of the Tm concentration while the green emission decreases. Such phenomena can be well explained by using the proposed energy diagram of the tridoped NaYF₄ nanocrystals. Furthermore, we demonstrated that this type of UCNP materials can be used in fabricating anti-counterfeiting labels with multi-level security features that can be revealed under various optical conditions. The developed tridoped UCNPs with their unique optical properties will significantly enhance the security level of next-generation anti-counterfeiting labels.

University of South Dakota
Chaoyang Jiang