Complete Dopant Substitution by Spinodal Decomposition in Mn-Doped Two-Dimensional CsPbCl₃ Nanoplatelets

The introduction of dopants plays a key role in the physical properties of semiconductors for optoelectronic applications. However, doping is generally challenging for nanocrystals (NCs), especially for two-dimensional (2D) NCs, due to the self-annealing effect and high surface energies required for dopant addition. Here, we report an efficient doping strategy for Mn-doped 2D CsPbCl₃ (i.e., Mn:CsPbCl₃) nanoplatelets (NPLs) through a postsynthetic solvothermal process. While the original lightly doped 2D Mn:CsPbCl₃ NPLs were obtained from growth doping, higher Mn doping efficiencies were achieved through diffusion doping under pressure-mediated solvothermal conditions, resulting in enhanced Mn photoluminescence (PL). Surprisingly, a new CsMnCl₃ phase with complete dopant substitution by spinodal decomposition was observed with extended solvothermal treatment, which is confirmed by powder X-ray diffraction, X-ray absorption fine structure, and electron paramagnetic resonance. Compared with Mn:CsPbCl₃ NPLs, the pure CsMnCl₃ NPLs give rise to shorter Mn PL lifetime, which is consistent with the short Mn-Mn distance within CsMnCl₃ NPLs. This work provides an efficient strategy for doping inside NCs as well as new insights on the dopant concentration-dependent structural and optical properties of perovskite NCs.