Highly Concentrated, Zwitterionic Ligand-Capped Mn 2+ :CsPb(Br x Cl 1- x ) 3 Nanocrystals as Bright Scintillators for Fast Neutron Imaging.

Fast neutron imaging is a nondestructive technique for large-scale objects such as nuclear fuel rods. However, present detectors are based on conventional phosphors (typically microcrystalline ZnS:Cu) that have intrinsic drawbacks, including light scattering, γ-ray sensitivity, and afterglow. Fast neutron imaging with colloidal nanocrystals (NCs) was demonstrated to eliminate light scattering. While lead halide perovskite (LHP) FAPbBr 3 NCs emitting brightly showed poor spatial resolution due to reabsorption, the Mn 2+ -doped CsPb(BrCl) 3 NCs with oleyl ligands had higher resolution because of large apparent Stokes shift but insufficient concentration for high light yield. In this work, we demonstrate a NC scintillator that features simultaneously high quantum yields, high concentrations, and a large apparent Stokes shift. In particular, we use long-chain zwitterionic ligand capping in the synthesis of Mn 2+ -doped CsPb(BrCl) 3 NCs that allows for attaining very high concentrations (>100 mg/mL) of colloids. The emissive behavior of these ASC18-capped NCs was carefully controlled by compositional tuning that permitted us to select for high quantum yields (>50%) coinciding with Mn-dominated emission for minimal self-absorption. These tailored Mn 2+ :CsPb(BrCl) 3 NCs demonstrated over 8 times brighter light yield than their oleyl-capped variants under fast neutron irradiation, which is competitive with that of near-unity FAPbBr 3 NCs, while essentially eliminating self-absorption. Because of their rare combination of concentrations above 100 mg/mL and high quantum yields, along with minimal self-absorption for good spatial resolution, Mn 2+ :CsPb(BrCl) 3 NCs have the potential to displace ZnS:Cu as the leading scintillator for fast neutron imaging.