Zn(II) alloying improves the luminescence efficiency of hybrid tetrahedral Mn(II) halides ((DMAPH) 2 MnX 4 ; X = Cl, Br, and I) to near-unity

Abstract

Zero-dimensional (0D) tetrahedral Mn(II) halides (MnX42– (X = Cl, Br, I)) have emerged as solid-state green emitters with high photoluminescence quantum yield (PLQY). However, their PLQYs are significantly dependent on the environment surrounding the Mn(II), i.e., the organic cation and the halide. Although the tetrahedral Mn(II) bromide is highly emissive, Mn(II) iodide exhibits relatively low PLQY. Herein, we report the preparation of organic–inorganic hybrid tetrahedral Mn(II) halides (Cl, Br, and I) using the organic cation protonated 4-dimethylaminopyridine ((DMAPH)+), and they all exhibit bright green luminescence with high PLQY (∼76%–80%), regardless of the halide ion. Surprisingly, DMAPH undergoes N-demethylation exclusively in the case of tetrahedral Mn(II) iodide. Furthermore, we find that the controlled Zn2+-doping/alloying in the Mn(II) halide lattice improves the PLQY to near-unity (∼88%–94%) and is stable for more than 60 days. The increase of the excited state decay time in time-resolved PL lifetime measurements revealed that the improved luminescence is due to reduced Mn(II)–Mn(II) interactions of the lattice upon replacing some of the Mn(II) with Zn(II). This is further supported by the Zn-alloying-induced hyperfine splitting of Mn(II) ions observed in the electron paramagnetic resonance (EPR) measurements. However, excess alloying reduces PLQY due to the decrease in the tetrahedral Mn(II) concentration in the lattice. These results demonstrate the fabrication of hybrid Mn(II) halide (Cl, Br, and I) single crystals with near-unity PLQY and provide design strategies to improve their PLQY by selective organic cations and doping/alloying.