Yan Yinzhou, He Jing, Wang Mengyuan, Yang Lixue, Jiang Yijian
Institute of Laser Engineering, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing 100124, China.
Key Laboratory of Trans-scale Laser Manufacturing Technology, Beijing University of Technology, Ministry of Education, Beijing 100124, China.
ACS Appl Mater Interfaces. 2022 Jun 1;14(21):24636-24647. doi: 10.1021/acsami.2c05144. Epub 2022 May 17.
Increasing upconversion luminescence (UCL) to overcome the intrinsically low conversion efficiency of upconversion nanoparticles (UCNPs) poses a fundamental challenge. Photonic nanostructures are the efficient approaches for UCL enhancement by tailoring the local electromagnetic fields. Unfortunately, such nanostructures are sensitive to environmental conditions, and the regulation strength is varied in flexible applications. Here, we report giant UCL enhancement from a flexible UCNP-embedded film coupled with a microsphere photonic superlens (MPS), by which the enhancement ratio of UCL is over 10-fold under 808 nm excitation down to 0.72 mW. The enhancement pathways of MPS-enhanced UCL are attributed to Mie-resonant nanofocusing for high excitation-photon density, optical whispering-gallery modes (WGMs) for fast radiative decay, and the directional antenna effect for far-field emission confinement. The contribution of optical resonance in the MPS to suppressing the phonon-induced nonradiative transition and thermal quenching is experimentally validated. The UCL quantum yield is therefore improved by 3-fold to 4.20% under 120 mW/cm near-infrared excitation, consistent with the enhancement ratio via the Purcell effect of WGMs. Furthermore, the MPS demonstrates the robust optical regulation capability toward flexible applications, opening up new opportunities for facilitating multiphoton upconversion in wearable optoelectrical devices for nanoimaging, biosensing, and energy conversion in the future.
提高上转换发光（UCL）以克服上转换纳米颗粒（UCNP）固有的低转换效率是一项根本性挑战。光子纳米结构是通过调整局部电磁场来增强UCL的有效方法。不幸的是，此类纳米结构对环境条件敏感，且在灵活应用中调节强度会有所不同。在此，我们报道了一种由嵌入UCNP的柔性薄膜与微球光子超透镜（MPS）耦合实现的巨大UCL增强，在808 nm激发下，当激发功率低至0.72 mW时，UCL的增强倍数超过10倍。MPS增强UCL的增强途径归因于用于高激发光子密度的米氏共振纳米聚焦、用于快速辐射衰减的光学回音壁模式（WGM）以及用于远场发射限制的定向天线效应。实验验证了MPS中的光学共振对抑制声子诱导的非辐射跃迁和热猝灭的贡献。因此，在120 mW/cm的近红外激发下，UCL量子产率提高了3倍，达到4.20%，这与通过WGM的珀塞尔效应实现的增强倍数一致。此外，MPS在灵活应用方面展现出强大的光学调控能力，为未来在可穿戴光电器件中促进多光子上转换用于纳米成像、生物传感和能量转换开辟了新机遇。
