Fabrication of photoluminescent thin films via tribochemical deposition of upconversion nanoparticles

Micro- and nano-scale manufacturing enables the creation of high-precision structures for diverse applications in optics, electronics, biomedical devices, and sensors. Tribochemistry, which harnesses friction-induced interfacial reactions, provides a promising route for film fabrication at these scales. Among various functional materials, upconversion nanoparticles (UCNPs) have gained significant attention over the years due to their unique characteristics, including anti-Stokes shifts, sharp emission peaks, resistance to photobleaching, and long luminescent lifetimes. In this study, lanthanide-doped UCNPs were investigated as tribofilm precursors for the fabrication of functionalized tribofilms responsive to near-infrared (NIR) light at both the micro- and nano-scale. Micro-scale fabrication experiments demonstrated that UCNPs could be successfully incorporated into iron oxide-based tribofilms after extended sliding, while retaining their luminescent properties. Secondary Ion Mass Spectrometry (SIMS) analysis revealed a layered tribofilm structure, with UCNPs predominantly concentrated in the upper and middle regions. At the nanoscale, in-situ AFM experiments showed that stable UCNPs tribofilm formation required the presence of iron oxide, which also account for the film’s limited thickness and high susceptibility to load-induced wear. This study demonstrates a viable strategy for integrating optical functionality into tribofilms, opening opportunities for tribochemistry-driven fabrication in sensing and micro/nanomanufacturing applications.