Near-Infrared Photodetector Based on UCNPs-Covered Violet Phosphorus

Violet phosphorus (VP) is a layered material developed in recent years with a tunable bandgap, high carrier mobility, and better thermal stability than its phosphorus allotrope, black phosphorus (BP). The bandgap of VP varies with thickness, ranging from 1.68 to 2.02 eV, with a high responsivity in the visible range. Combining lanthanide-doped upconversion nanoparticles (UCNPs) with VP and taking advantage of the energy transfer between them is a feasible strategy to achieve near-infrared (NIR) photodetection and expand the application scenarios of devices. In this work, we designed a novel strategy for NIR detection by simply combining UCNPs and VP using the spin-coating method. The prepared UCNPs/VP photodetector exhibits an excellent photoresponsivity of 2.8 mA/W and a high specific detectivity of 2.04×10⁹ Jones (@ 980 nm, 2.8 mW/cm², 10 V). Compared to the weak photoresponse of bare VP, the UCNPs/VP device shows a significant improvement in photoresponse in the near-infrared band. Additionally, we conducted the photoresponse characterization of the UCNPs/VP device at different temperatures, aiming to enhance its performance by adjusting the temperature. In conclusion, we found that the hybrid device performs better in high-temperature environment. This work provides new ideas and approaches for VP-based optoelectronic devices.