Boosting Trapping in Dark Mode and Emission in Bright Mode using a Quad‐Nanohole

Abstract Single‐emitter luminescence is attractive for various applications, including single‐molecular biology, super‐resolution optical imaging, and single‐photon sources. Optical trapping as a particle positioning method is promising for enhancing luminescence by a precise matching of the nanoemitter to the sub‐wavelength mode volume of the photonic structure. Simultaneously satisfying the requirement of both luminescence and trapping enhancement, however, is challenging. Here, stable optical trapping and the in situ excitation of highly bright photoluminescence of a single up‐conversion nanoparticle (UCNP) are demonstrated. A quad‐nanohole structure with two bright‐field modes for enhanced excitation and emission of the UCNP, as well as a dark‐field mode for enhanced optical trapping is designed. It is experimentally demonstrated that the photoluminescence of the UCNP optically trapped in the quad‐nanohole is enhanced by a factor of 87 (as compared to a UCNP trapped in the single nanohole), and this enhancement factor surpasses that from a bowtie nanohole—one of the “gold standards” for local field enhancement. This work provides a route to assemble super‐bright single‐emitter luminescence by optical trapping.