Negative Thermal Quenching and Self-Trapped Exciton Emission in (R/S-C3H10ON)MnCl3

Thermal quenching presents a significant challenge for various phosphors, particularly in high-temperature applications. Therefore, uncovering novel optical characteristics such as negative thermal quenching (NTQ) holds promise for enhancing the efficiency of light-emitting diodes (LEDs). In this context, we have designed two new organic–inorganic hybrid halides, (R/S-C3H10ON)MnCl3, which crystallize in the P212121 space group featuring infinite chains of edge-sharing Mn octahedra. The presence of organic amine bonded to the Mn centers induces substantial octahedral distortion, resulting in self-trapped exciton (STE) emission. This STE emission is evident from a significant Stokes shift, a broad emission band, a prolonged photoluminescence (PL) lifetime, intense electron–phonon coupling, and a pliable lattice structure. Our density functional theory (DFT) calculations reveal localized excitonic states indicative of STE emission. With an increase in temperature, more number of STEs are generated, leading to the NTQ phenomenon.