Fabrication of upconversion‑particle‑doped polymer‑dispersed liquid crystal films with near‑infrared‑excited luminescence for anti‑counterfeiting applications

Traditional polymer-dispersed liquid crystals (PDLC) typically exhibit response delays when doped with photothermal conversion particles that respond to infrared stimulation. To overcome these limitations, this study proposes a PDLC composite doped with upconversion particles. By appropriately adjusting the content of the fluorinated monomer TFPMA and the loading of upconversion particles, the optical contrast of the PDLC was optimized to 102.09. Screen printing and laser etching techniques were used to fabricate pre-patterned PDLC anti-counterfeiting devices. The encrypted information remains concealed under ambient conditions and can be decoded via two independent pathways. Electric fields modulate the PDLC to switch its transparency, while upconversion particles emit light upon excitation by near-infrared light. The mutual independence of the electrically driven and photoluminescent channels provides great flexibility in encryption, supporting complex security architectures and multiple decryption paths. Unlike traditional photothermal PDLC systems, the composite material developed in this study bypasses the thermally mediated LC modulation process. Optical readout is achieved through upconversion luminescence, thereby overcoming the limitation of invisible response signals. This work provides a convenient and versatile approach for developing high-performance PDLC anti-counterfeiting composite materials.