Record‐High Responsivity and High Detectivity Broadband Photodetectors Based on Upconversion/Gold/Prussian‐Blue Nanocomposite

The development of high‐quality and strongly Au conjugated upconversion nanoparticles (UCNPs) is time‐consuming and requires specific chemicals. Therefore, a one‐pot hydrothermal method is adopted for novel in situ preparation of UCNP@Au composites using a binary functional ethylenediaminetetraacetic salt, which is employed as a surfactant and reducing agent. The composites are electrostatically conjugated with metal‐coordinated Prussian blue (PB) to yield UCNP@Au+PB nanocomposites (NCs), which demonstrate 21‐fold upconversion emission quenching by fluorescence resonance energy transfer compared to UCNPs. Additionally, the PB, UCNP@Au, and NCs demonstrate a synergistically reduced trap (α ≈ 0.85) and enhance ultrasensitive broadband (432–980 nm) photodetection. The NCs‐based gate‐free epitaxial graphene device demonstrates excellent high photoresponsivity (5.9 × 105 A W–1), detectivity (2.17 × 1014 cmHZ​W−1${\rm{cm}}\sqrt {{{\rm{H}}_{{\rm{Z}}} {{\rm{W}}^{{\bm{ - }}1}}$), and normalized gain (2.06 × 10−4 m2 V–1) at 318 nW cm–2 (532 nm) and a bias voltage of 1 V. The Au plasmons enhance the one‐photon‐enabled visible absorption of Er3+ ions, and PB exhibits broad absorption and enhances the carrier density of the device, resulting in an ultrahigh photoresponse. The obtained device performance is the highest to date among their class of nanohybrids. Also, these NCs can readily detect polychromatic light and signals from daily‐use appliances, indicating their potential for applications in consumer electronics. A novel metal‐coupled upconversion‐nanoparticle‐based nanocomposite is synthesized in situ by a one‐step hydrothermal method. The nanocomposite‐based device demonstrates record‐high photoresponsivity (5.9 × 105 A W‐1) and high detectivity (2.17 × 1014 cmHZW−1${\rm{cm}}\sqrt {{{\rm{H}}_{\rm{Z}}} {{\rm{W}}^{ - 1}}$) at 318 nW cm‐2 (532 nm) and a bias voltage of 1 V. The performance of the device is the highest to date among its class of nanohybrids.