Zn(II) Alloying Improves the Luminescence Efficiency of Hybrid Tetrahedral Mn(II) Halides ((DMAPH)₂MnX₄; X = Cl, Br, and I) to Near-Unity

Abstract

Zero-dimensional (0D) tetrahedral Mn(II) halides (MnX4 2– (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.

Near-unity photoluminescence quantum yield in zero-dimensional lead-free indium-based hybrid perovskites by antimony doping

“…24,25 Constructing single crystal materials with zero-dimensional (0D) structures by using larger organic cations is an efficient approach to obtain suitable host–guest systems, because larger organic cations make it easier for luminescent substances to be regularly embedded in the matrix. 26–28 Due to the strong electron–phonon coupling effect, the formation of self-trapped excitons (STEs) is more likely in this 0D structure. 29–31 In particular, STE state formation in a 0D isolated polyhedron structure is closely related to dielectric confinement effects and structural distortion, which is one reason for the higher PLQY.…”

Enhancing the Water‐Stability of 1D Hybrid Manganese Halides by a Cationic Engineering Strategy

“…[ 21–24 ] Furthermore, the stannum(II), copper(I) and cerium(II) with low valence states are easily oxidized in an atmospheric environment, especially in the presence of a trace amount of water, leading to material instability. [ 25–27 ] Therefore, exploring water‐stable lead‐free hybrid halides is pivotal for more expansive optoelectronic application fields.…”

Tailoring the π–π stacking interaction among organic cations in hybrid metal halide crystals towards tunable light emission

“…0D OIMHs with optically active ions such as Mn 2+ and Sb 3+ as a metal center always feature typical optical emission due to the intrinsic electronic transition of these metal ions. 12–15 For instance, the (MTP) 2 MnBr 4 (MTP: methyltriphenylphosphonium) 12 and (BZA) 2 SbCl 5 (BZA = 2,4-diamino-6-phenyl-1,3,5-triazine) 13 crystals which possess a 0D structure display strong blue and orange emissions under the excitation of ultra violet (UV) light. However, in OD OIMHs with Zn 2+ or Cd 2+ as metal centers, the optical emission mostly originates from the electronic transition of the organic component or the self-trapped excitons (STEs).…”