Neutron detection materials are critical and irreplaceable in the fields of nuclear security monitoring, radioactive waste management, and particle physics research. The development of efficient neutron-gamma multimode scintillators that simultaneously offer high light yield, decent energy resolution, and efficient neutron-gamma discrimination capability remains a grand challenge. In this work, we report a neutron-gamma discrimination strategy by introducing ${}^6\mathrm{Li}$-enriched $\mathrm{Li}\mathrm{I}$ dopants, which has a high thermal neutron absorption cross section, into the highly efficient ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl}$ single crystals. The Bridgman-grown ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl},\mathrm{Li}$ single crystals demonstrate superior light yield of 81 000 photons/MeV under gamma irradiation and 200 000 photons/neutron under thermal neutron irradiation, respectively, higher than any reported multimode scintillators. Moreover, ${\mathrm{Cs}}_3{\mathrm{Cu}}_2{\mathrm{I}}_5:\mathrm{Tl},\mathrm{Li}$ single crystals possess a superior energy resolution of 4.2% at 662 keV, a decent neutron-gamma discrimination figure of merit of 2.35, and an intrinsic absence of radioactive background. By combining the density-functional-theory calculations, nuclear magnetic resonance, positron annihilation, and thermoluminescence measurements, the effects of ${}^6\mathrm{Li}$ codoping on the defect structure and scintillation performance were clarified. This work provides an alternative horizon for designing highly efficient neutron-gamma multimode scintillators.

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• Crystal growth
• Doping effects
• Gamma ray spectroscopy
• Neutron techniques
• Scintillators