Photochemical Anchoring of Singly Er³⁺ Ion-Doped NaYF₄ Nanoparticles for Scalable Fabrication of Single-Photon Emitting Devices: Implications for Quantum Light Sources in the Telecom Window

Scalable methods to access single-photon sources on demand are highly sought after. As a potential strategy, we demonstrate the optical trapping and chemical anchoring of NaYF4 nanoparticles (NPs) and NaYF4 NPs doped with on average a single Er3+ ion. The anchoring method we present involves surface coating the NPs with thiol-functionalized phospholipids, where the thiol group is protected with a chemical group photoremovable at 340 nm 2-bromo-4′-hydroxyacetophenone. Functionalized NPs are trapped optically in a gold double-nanohole aperture using a 980 nm laser. A 340 nm light beam is focused on the particle, resulting in deprotection of the thiol groups and attachment of the thiols to the gold surface, permanently anchoring the NPs. Electron microscopic imaging proves the successful anchoring after removal of the trapping laser, 340 nm light source, and solvent. The approach is promising for reliably fabricating a single-photon emitting material in a scalable and potentially automatable manner.