• • Optimal stoichiometry n(CsI)=0.62 yields crack-free, inclusion-free Cs3Cu2I5 crystals with a photoluminescence quantum yield (PLQY) of 79.3%, directly improving scintillator fabrication yield and reducing optical losses.
• • The optimized crystal achieves a light yield of 24,380 photons/MeV and an energy resolution of 3.8% at 662 keV (137Cs), surpassing many conventional scintillators and enabling superior gamma-ray spectroscopy.
• • Exciton binding energy of 473.9 meV and Huang-Rhys factor S=79.8 confirm strong exciton-phonon coupling, which underpins efficient self-trapped exciton emission and guides material engineering for further performance tuning.
• • Dominant decay time of 957 ns and excellent linear response in the medium-to-high energy region make the material suitable for applications requiring timing resolution and quantitative gamma-ray detection.