Size-Dependent Doping Synergy and Dual-Color Emission in CsPb1-xMnxCl₃ Nanocrystals

The doping of atomic impurities into colloidal semiconductor nanocrystals (NCs) is a powerful way to tune optical and electronic properties. Manganese (Mn)-doped CsPbCl3 NCs in particular show dual exciton/dopant emission in the visible spectrum, making them materials of current interest for optoelectronic applications. Here, we examine the impact of Mn doping on the photophysics of CsPbCl3 NCs from a different perspective. Using ultracentrifugation, we extract size-resolved fractions from a series of parent NC suspensions prepared at varied doping levels, and we measure the photoresponse as a function of NC size. Our results reveal synergistic radiative effects, with large enhancements in both blue (exciton) and red (dopant) quantum yield (QY) over a narrow range of Mn concentration. We ascribe the first effect to defect passivation and the latter to efficient exciton–dopant charge transfer near a critical point in the number of Mn per NC where the dopant spacing coincides with the Bohr exciton radius. Advanced computational techniques applied to Mn-doped CsPbCl3 reproduce emission colors and concentration trends, with a drop in QY at higher doping levels. Our results offer additional insight into the photophysical interplay of doping, quantum confinement, and radiative relaxation in lead-halide perovskites, while clarifying the complexity of the underlying kinetics and highlighting the critical role of the dopant number per NC at the nanoscale.