Suppressed Concentration Quenching Via Divalent Eu/Sr Alloying in Hybrid Iodides Scintillators Toward Bright Luminescence for X‐ray Imaging

Abstract Overcoming concentration quenching in rare‐earth‐activated luminescent materials always remains a challenge for enhancing photoluminescence quantum yield (PLQY). Herein, we report two divalent Sr‐based hybrid iodides, (Ph 3 MeP)SrI 3 and (Ph 3 EtP)SrI 3 (Ph 3 MeP = methyltriphenylphosphonium, Ph 3 EtP = ethyltriphenylphosphonium), and equivalent Eu/Sr alloying have been identified experimentally in the full range of 0 ≤ x ≤ 1 for (Ph 3 MeP)Sr (1‐ x ) Eu x I 3 and (Ph 3 EtP)Sr (1‐ x ) Eu x I 3 . These Eu/Sr‐based hybrid iodides exhibit 1D [Sr (1‐ x ) Eu x I 6 ] 4− octahedra chains, suppressing nonradiative energy loss effectively by maintaining optimal spacing and dispersion between adjacent Eu(II) emission centers. Upon even heavily Eu(II) alloying, (Ph 3 MeP)Sr 0.5 Eu 0.5 I 3 exhibits efficient green emission ( λ em = 525 nm) with a high PLQY of ∼92.2%. Accordingly, it achieves a high scintillation light yield of 54 000 ± 300 ph MeV −1 and a low detection limit of 49.9 nGy s −1 . Furthermore, ceramic wafers counterparts of Eu/Sr alloy prepared via cold sintering process demonstrate high‐resolution X‐ray imaging with a spatial resolution up to 15.7 lp mm −1 . These findings not only present a new family of hybrid bimetallic iodides via Eu/Sr alloying, but also provides structurally guided strategy to suppress concentration quenching toward bright luminescence for scintillation applications.