Rapid Identification of Nanoscale Point Defects in Two-Dimensional Crystals by Rare-Earth-Enhanced Fluorescence

Identifying nanoscale point defects (NPDs) is essential for producing high-quality two-dimensional (2D) crystals and moving them towards scalable device integration. However, existing methods face a fundamental compromise between spatial resolution and detection throughput: atomic-resolution techniques provide limited testing area or sampling rates, whereas conventional optical methods often lack sufficient sensitivity required for low-density NPDs. Here, we present a highly sensitive, non-destructive strategy that employs erbium chloride (ErCl₃) to form erbium-rich nanoparticles (Er-NPs) as fluorescent markers at NPD sites on 2D crystal surfaces, enabling rapid and precise mapping of NPDs in large-area samples. Both theoretical modeling and experimental observations demonstrate that Er-NPs preferentially accumulate at defect sites, substantially enhancing localized photoluminescence (PL) signals and enabling direct visualization of NPD locations and distributions. This approach complements established optical techniques, including Raman spectroscopy, by providing higher-contrast and more efficient localization of low-density nanoscale defects across large-area samples. Importantly, Er-NPs can be fully removed through annealing under ultrahigh vacuum (UHV), ensuring the non-destructive nature of the method. This work provides a powerful tool for quality control of 2D materials, supporting their transition from laboratory synthesis to large-scale industrial applications.