Upconverting Near‐Infrared Light Detection in Lead Halide Perovskite with Core–Shell Lanthanide Nanoparticles

Abstract

Light detection in the near‐infrared (NIR) region is necessary in a wide range of optical applications, such as optical communication, medical diagnostics, and environmental analysis. Herein, a novel NIR detection method based on energy conversion by upconversion (UC) materials is demonstrated. Nanoparticles (NPs) containing erbium (Er) ions are used as the UC material. Conventional NPs that contain ≈2 mol% Er ions have very weak light absorption ability, which is dramatically improved by incorporating high concentrations of Er ions (≈100 mol%). By coating the NP surfaces with inorganic perovskite containing heavy atoms (CsPbBr3) instead of organic alkyl chains, the thermal vibrations that deactivate the UC emission are suppressed effectively, resulting in high UC emission quantum efficiency of >5%. The perovskite coating process facilitates the introduction of the NPs into CsPbI3 thin films (which absorbs visible light only) and forms highly crystalline and uniform thin films. The resulting CsPbI3 thin film can be excited with NIR light, showing the emission from CsPbI3 via the UC. This enables fabrication of a UC‐based photodetector generating a photocurrent signal through the energy conversion process from NIR to visible light. The photodetector shows a high responsivity to weak NIR light with the quantum conversion efficiency of 75%.