Exploring the limits of 3D dopant localization in phosphor nanoparticles: A simulation-to-experiment perspective via through-focus HAADF-STEM

Accurate three-dimensional (3D) localization of rare-earth dopants in crystalline phosphor nanoparticles (NPs) remains a critical challenge for understanding structure-property relationships and optimizing luminescent performance. Through-focus High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) offers promising depth sectioning for bulk materials, but its systematic application to beam-sensitive NPs is unexplored. We investigate through-focus HAADF-STEM feasibility for 3D dopant distributions in SrF2:Eu NPs via a comprehensive simulation-to-experiment approach, addressing complex channeling effects. Multislice simulations reveal that electron channeling along Sr atomic columns significantly broadens the electron probe and introduces systematic positioning errors at greater depths. A developed depth correction function accounts for channeling effects, achieving high localization accuracy for individual Eu atoms in simulated focal series. Critical spatial resolution limits for multiple dopant detection have been established, as individual dopants become indistinguishable due to overlapping channeling effects. Experimental implementation has revealed fundamental practical constraints limiting through-focus analysis of SrF2:Eu NPs. Beam damage and specimen instability (such as rigid-body motion or beam-induced atomic displacement), pronounced in NPs, critically compromise localization precision. Despite unachieved 3D dopant characterization for these NPs, this investigation establishes quantitative frameworks for understanding through-focus HAADF-STEM capabilities and limitations in beam-sensitive crystalline systems. Developed correction methodologies guide future implementations in more stable materials, while systematic characterization of damage and stability defines realistic boundaries for NP depth sectioning.