Cu²⁺-Facilitated Formation of Mn²⁺-Mn²⁺ Dimers Inducing Redshift of Mn²⁺ Emission in Co-Doped Perovskite Nanocrystals

Transition metal doping in perovskite nanocrystals is an important means to regulate their photophysical properties. In particular, the underlying concentration effect and optical process deserve further study. Herein, we investigate the phenomenon of continuous redshift in manganese-doped perovskite nanocrystals spectra with the Mn2+ doping concentration. The results from experiment combined with density functional theory (DFT) show that the spectral redshift primarily results from the heightened emission of Mn2+-Mn2+ dimers and the reduced contribution of isolated Mn2+ as the concentration of Mn2+ increases. What is more, appropriate introduction of Cu²⁺ ions with a Cu to Pb molar ratio of 1:1 can increase the formation energy of Mn-related defects, facilitate the formation of Mn²⁺-Mn²⁺ dimers, and simultaneously inhibit the non-radiative recombination process caused by the close spacing of Mn ions, thereby avoiding the occurrence of fluorescence quenching, thus the redshift of spectra is significant in the presence of Cu2+ ion. These findings enhance comprehension of the photoluminescence mechanism related to spectral redshift in nanocrystals doped with transition metals.