Spatial remote luminescence enhancement by a half-cylindrical Au groove

Abstract

Enhancing the luminescence emission from upconversion nanoparticles (UCNPs) is crucial to reduce the limits of biosensing based on UCNPs. Photonic crystal and surface plasmon structures have been used to enhance the emission of phosphor, while the enhancement distance is only limited to the near-field range. For in vitro biodetection, the distance between the UCNP and the substrate is usually in the far-field range. This work proposes the use of a half-cylindrical gold groove to enhance the emission of UCNPs even when the nanoparticles are at a far-field distance from the substrate. Due to scattering, constructive interference and coupling of optical modes in the Au groove, large-area/far-field range resonance modes can be created. Efficient resonance coupling between the optical mode and the excitation/emission of UCNPs can occur in the far-field range, which is able to enhance the absorption, quantum yield, extraction and collection of emission of UCNPs. The enhancement region is not only limited to the near-field range of the structure but also expands to the far-field range of the structure. By comparing different shapes and materials of the grooves, the proposed structure can improve the emission by 8.25 times when the UCNP is 4.4 μm away from the bottom of the groove compared with the bare glass. Besides, our structure is experimentally feasible and will greatly contribute to the development of high sensitivity and high SNR fluorescence biosensors.