Efficient　and　stable　scintillators　play　a　crucial　role　in　X-ray　detection　applications.　To　enhance　the　luminescence　efficiency　under　X-ray　excitation,　the　incorporation　of　multiple　emission　centers　into　scintillators　is　widely　explored.　Here,　it　is　found　that　the　cesium　copper　halide　Cs5Cu3Cl6I2　exhibits　dual　emission　centers,　enabling　high-performance　scintillators　with　an　X-ray　light　yield　of　49000 photon MeV−1　and　a　low　detection　limit　of　4 nGy s−1.　The　emissions　of　Cs5Cu3Cl6I2　are　from　intrinsic　self-trapped　exciton　(STE)　and　Frenkel　defect-assisted　STE.　High-energy　X-rays　can　induce　an　increased　fraction　of　Frenkel　defect-assisted　STEs,　which　can　serve　as　an　effective　scintillation　channel.　Furthermore,　large-area　flexible　scintillators　with　a　high　resolution　of　18 lp mm−1　are　developed,　making　them　suitable　for　X-ray　imaging　applications.　These　findings　offer　promising　insights　for　developing　more　efficient　scintillators.　©　2024　Wiley-VCH　GmbH.