High-Sensitivity Near-Infrared Upconversion Detector Using Hybrid Plasmonic-Photonic Structure

In an array-format optical-readout configuration, near-infrared (NIR) upconversion detectors transform NIR excitation into visible emission that can be recorded by standard cameras, enabling direct imaging without complex readout circuits. However, these optical-readout upconversion detectors typically rely on lanthanide-doped transducers, and their performance is often constrained by the intrinsically weak NIR absorption of 4f-4f transitions and the nonlinear multiphoton excitation dynamics, which together reduce the excitation-to-emission conversion yield and ultimately limit detectivity of the device. Here, we report a camera-readable NIR upconversion detector based on a UCNPs-PDMS microarray integrated with cascaded plasmonic and photonic field-modulation elements. In this configuration, resonance-matched Au nanorods (Au NRs) provide nanoscale near-field amplification, while a pitch-matched polydimethylsiloxane (PDMS) microlens array (MLA) concentrates the excitation light at the detector plane. The cascaded hybrid architecture delivers more than 8-fold enhancement in raw upconversion luminescence. Under fixed camera and image-processing settings, the noise-equivalent irradiance (NEI) falls from 83.98 to 0.674 mW·cm^-2 and the effective optical-readout specific detectivity increases from 2.17 × 10³ to 2.70 × 10⁵ Jones, yielding a 124.6-fold enhancement in overall device detection performance. A time-lapse drying demonstration further validates stable, quantitative optical-readout monitoring sensing, where the extracted ratio metric follows a Page-model form and yields kinetic descriptors of moisture evolution.