Upconversion Amplification through Aggregation Modulation in a Multimodal Luminescent System

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted interest in broad fields but are hindered by intrinsic low photon responsiveness. To overcome the limitation, many strategies have been developed to enhance the performance of UCNPs, including dye sensitization, core–shell engineering, photonic crystal engineering, and so on. While the luminescence intensity has been improved by these methodologies, the terms of luminescence mode diversity have not been further enriched and tunable, such as the wavelength and lifetime, which are from the UCNPs only. In addition, these methodologies are based on a cumbersome preparation process. Herein, we develop an approach to modulate the aggregation of UCNPs through the persistent luminescence (PersL) micrometer particles for upconversion luminescence enhancement. Compared to the individual UCNPs in ethanol, in which emissions are quenched in all directions, the emission of UCNP aggregation on the surface of the PersL micron particles is significantly preserved from quenching. In addition, the near-infrared absorption is increased in UCNP aggregation through the multiple reflection–absorption effect. With the cooperative efforts of suppressive quenching and the enhanced interaction between the incident light and luminescent ions, the UCNPs-PersL systems achieve about a 2-fold enhanced upconversion. Furthermore, promising applications in the realm of dynamic anticounterfeiting have been demonstrated. Thus, this strategy not only realizes enhanced upconversion by modulating the aggregation of UCNPs but also endows the hybrid system with multimodal luminescence.