Rare‐Earth Mediated Engineering in ZnSe@ZnS:Eu ³ ⁺ to Simultaneously Achieve Structural Modulation and Atomic Eu Doping Sites for X‐Ray Imaging

Lanthanide ions offer distinctive optical features but have weak absorption due to parity‐forbidden 4f‐4f transitions, prompting strategies to boost absorption through host matrices, dopant engineering, and optimized nanostructures. Ln‐doped colloidal QDs enhance photoluminescence and broaden absorption for applications in solar energy and photo‐catalysis, yet integrating Ln 3+ into hosts and achieving efficient energy transfer, especially in Ln‐doped II‐VI sulfide QDs, still remains challenging and unsolved. Here, we report a “dual hard‐base anchoring” strategy for synthesizing rare‐earth doped ZnSe@ZnS:Eu 3+ QDs. Interestingly, based on the fluoride‐oleylamine synthetic interactions, Eu 3+ forms atomic Eu doping sites on the QD surface, as shown by extended X‐ray absorption fine‐structure analysis. Optimized temperature, Eu 3+ doping, and F − concentration yield controlled morphologies, including tetragonal growth, tip, island, and coupled flower forms. Surface passivation with oleylamine and a 1,10‐phenanthroline ligand broadens Eu 3+ ‐related emission ( 5 D 0 → 7 F 2 / 7 F 1 ). The approach also applies to six other rare‐earth dopants, delivering high performance in X‐ray imaging and enabling rare‐earth related new applications.