Lead halide perovskite nanocrystals have recently demonstrated great potential as x-ray scintillators, yet they still suffer toxicity issues, inferior light yield (LY) caused by severe self-absorption. Nontoxic bivalent europium ions (Eu2+) with intrinsically efficient and self-absorption-freed–ftransition are a prospective replacement for the toxic Pb2+. Here, we demonstrated solution-processed organic–inorganic hybrid halide BA10EuI12(BA denotes C4H9NH4+) single crystals for the first time. BA10EuI12was crystallized in a monoclinic space group ofP21/c, with photoactive sites of [EuI6]4−octahedra isolated by BA+cations, which exhibited high photoluminescence quantum yield of 72.5% and large Stokes shift of 97 nm. These properties enable an appreciable LY value of 79.6% of LYSO (equivalent to ~27,000 photons per MeV) for BA10EuI12. Moreover, BA10EuI12shows a short excited-state lifetime (151 ns) due to the parity-allowedd–ftransition, which boosts the potential of BA10EuI12for use in real-time dynamic imaging and computer tomography applications. In addition, BA10EuI12demonstrates a decent linear scintillation response ranging from 9.21 μGyairs−1to 145 μGyairs−1and a detection limit as low as 5.83 nGyairs−1. The x-ray imaging measurement was performed using BA10EuI12polystyrene (PS) composite film as a scintillation screen, which exhibited clear images of objects under x-ray irradiation. The spatial resolution was determined to be 8.95 lp mm−1at modulation transfer function = 0.2 for BA10EuI12/PS composite scintillation screen. We anticipate that this work will stimulate the exploration ofd–ftransition lanthanide metal halides for sensitive x-ray scintillators.