Luminescent nanoparticle-arrays synthesized via polymer pen lithography

We report a high-throughput approach to generating lanthanide-doped upconversion nanoparticle (UCNP) arrays through polymer pen lithography (PPL), where instead of the expensive block co-polymer, two types of polymers are employed with one working as ink carrier, e.g., polyethylene glycol-400 (PEG-400) to facilitate smooth transfer from the tip to the substrate and the other, e.g., polyvinyl pyrrolidone (PVP), as chelator to ensure successful patterning of metal ions. The strong coordination of PVP with rare earth ions (RE³⁺) is the key for weakening the interaction between RE³⁺ ions and the carrier PEG-400 so that the good mobility of ink can be retained. Further experimental results have shown that besides PVP, small molecules with functional groups that can coordinate with RE³⁺ ions, such as oleic acid, can also serve the same role as PVP, which greatly enriches the ink library for PPL. Over 1 cm² area arrays comprising individual UCNP can be reliably generated with characteristic upconversion luminescence. This strategy not only allows reliable production of individual UCNP arrays, it also paves new avenue to the precise synthesis of multifunctional NPs for lasing, imaging, encryption, and anticounterfeiting.