Enhanced Photoluminescence in Hybrid Manganese Halides via Halogen Regulation for LED Applications

Organic-inorganic Mn(II)-based halides have aroused a great deal of attention due to their unique optoelectronic properties. Selecting the appropriate valence and size of organic groups and adopting halogen regulation of inorganic genes are two effective strategies to enhance the luminescence properties of Mn(II)-based halides. Herein, two new zero-dimensional (C₈H₁₈N)₂MnX₄ (X = Cl and Br) compounds were synthesized by choosing monovalent and large <i>N</i>-ethylcyclohexylaminium (C₈H₁₇N⁺) to combine [MnCl₄]^2- and [MnBr₄]^2- tetrahedra, respectively. They exhibit bright green-light emission with maximum peaks centered at 530 and 525 nm and lifetimes of 3.0 ms and 294 μs for (C₈H₁₈N)₂MnCl₄ and (C₈H₁₈N)₂MnBr₄, respectively. Amazingly, the photoluminescence quantum yield (PLQY) was significantly enhanced from 33.87% to 81.12% when Cl^- was replaced with Br^-. Moreover, both crystals exhibit high thermal, environmental, and optical stability. Theoretical calculations reveal that the photoluminescence of both (C₈H₁₈N)₂MnX₄ (X = Cl and Br) compounds originated from [MnX₄]^2- tetrahedra, namely, the radiative recombination of the ⁴T₁ → ⁶A₁ spin-forbidden transition of Mn²⁺. To demonstrate practical optoelectronic applications, LED devices were assembled by using (C₈H₁₈N)₂MnX₄ (X = Cl and Br) crystals, exhibiting remarkable color stability. This work not only presents promising applications of (C₈H₁₈N)₂MnX₄ in solid-state lighting but also provides an effective strategy to design novel Mn(II)-based halides with outstanding photoluminescence.