NaYF 4 : Er 3+ Nanoparticles‐Graphene Photodetector for High‐Responsivity 1.5 µm Narrowband Imaging and Multi‐Wavelength Sensing

Silicon‐based photodetection in the 1.5 µm spectral window is important for next‐generation photonic systems, enabling critical applications in optical communication, LiDAR, and atmospheric gas sensing. Although erbium‐based upconversion photodetectors (UPDs) offer advantages in cost‐effective fabrication and stable spectral selectivity, their deployment is fundamentally limited by compromised responsivity, slow response times, and complex multilayer architectures that hinder scalability. Here, we report a UPD that synergistically integrates high‐efficiency Er‐based nanoparticles (ENPs) with an engineered graphene photogating architecture. Fabricated on SiO 2 /p+‐Si substrates, the optimized device achieves unparalleled performance metrics: a record‐high responsivity of 59.5 A/W at 1 V bias, millisecond‐scale response dynamics, and narrowband 1.5 µm detection. This exceptional performance originates from two synergistic mechanisms: the ENPs' high upconversion quantum yield (2.1%) and a substantial photoconductive gain (∼10 7 ) from the graphene photogating, increasing responsivity by a factor of 5 over conventional designs. Additionally, leveraging the intrinsic narrowband response of ENPs, we demonstrate a dual‐channel wavelength‐selective structure capable of effectively discriminating signals within the 1.5 µm band from those below 1.1 µm. This permits simultaneous multi‐wavelength detection, as demonstrated via spatially‐resolved imaging at 633 and 1523 nm. Combined with its fabrication simplicity and scalability, this work represents a significant leap forward for high‐performance UPDs.