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

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, (Ph₃MeP)SrI₃ and (Ph₃EtP)SrI₃ (Ph₃MeP = methyltriphenylphosphonium, Ph₃EtP = ethyltriphenylphosphonium), and equivalent Eu/Sr alloying have been identified experimentally in the full range of 0 ≤ x ≤ 1 for (Ph₃MeP)Sr_{(1- x )}Eu_xI₃ and (Ph₃EtP)Sr_{(1- x )}Eu_xI₃. These Eu/Sr-based hybrid iodides exhibit 1D [Sr_{(1- x )}Eu_xI₆]^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, (Ph₃MeP)Sr_0.5Eu_0.5I₃ 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.