Meanwhile, the emission of Mn2+ decreases with the increasing Cl- content, which is caused by different thermal quenching of Mn2+ emission in the mixed Cl-/Br- coordination.  The former is due to the different thermal quenching for different coordinations of Mn2+ with Cl- and Br-, while the latter is due to the weaker spin-orbit coupling of the Mn2+ ion caused by the interaction with the lighter Cl- ions, which makes the spin selection rule stricter and leads to a longer lifetime of Mn2+ consequently.
THERM