Mid-infrared detection through ligand-driven local heating in lanthanide-doped nanoparticles

Mid-infrared photothermal detection, leveraging well-established visible/near-infrared detection techniques, holds significant potential for a wide range of scientific and industrial applications. Conventional mid-infrared photothermal methods show limited response at weak mid-infrared radiation due to insufficient thermal sensitivity. Here, we overcome this challenge by employing ligand-capped lanthanide nanoparticles, where organic molecules with strong and broadband mid-infrared absorption serve as localized heating sources under MIR irradiation. The increased temperature modulates the ratiometric photoluminescence of lanthanide ions via thermally sensitive energy transfer processes. This thermally mediated mechanism enables broadband (5-10 μm) mid-infrared detection at room temperature, achieving a detectivity of 4.8 × 10⁸ Jones at 6.3 μm. The system exhibits a response time of approximately 2 ms and demonstrates spectral fidelity and gas sensing performance competitive with state-of-the-art Fourier-transform infrared systems. Our results establish a new design paradigm for mid-infrared photodetection that bridges molecular photonics and nanotechnology, paving the way for next-generation optical sensing platforms.