Proposed mechanism of proton scintillation in a CsPbBr 3 nanocrystal. Process 1 represents multiple exciton generation via impact ionization. Process 2 represents the second route for multiple exciton generation via below-bandgap low-energy δ-ray pumping. The biexcitons are converted from the excitons formed via processes 1 and 2. Subsequently, de-excitation from the biexcitonic state (| XX ) to the excitonic state (| X ) results in the emission of ionoluminescence photons at 537 nm (2.32 eV). De-excitation from the excitonic state (| X ) to the ground state (|0) results in 526 nm emission ( E g , 2.36 eV). Note that the virtual state |2 X corresponds to an energy level of 2 E g . e − , electron; h + , hole.
