Fluorescent Alloy CsPb Mn_1- I₃ Perovskite Nanocrystals with High Structural and Optical Stability

CsPbI₃ nanocrystals are still limited in their use because of their phase instability as they degrade into the yellow nonemitting δ-CsPbI₃ phase within a few days. We show that alloyed CsPb Mn_1- I₃ nanocrystals have essentially the same optical features and crystal structure as the parent α-CsPbI₃ system, but they are stable in films and in solution for periods over a month. The stabilization stems from a small decrease in the lattice parameters slightly increasing the Goldsmith tolerance factor, combined with an increase in the cohesive energy. Finally, hybrid density functional calculations confirm that the Mn²⁺ levels fall within the conduction band, thus not strongly altering the optical properties.