Highly Efficient and Tunable Emission of Lead-Free Manganese Halides toward White Light-Emitting Diode and X-Ray Scintillation Applications

Environmental friendly metal halides have become emerging candidates as energy downconverting emitters for lighting and X-ray imaging applications. Herein, luminescent single crystals of tetramethylammonium manganese chloride (C₄H₁₂NMnCl₃) and tetraethylammonium bromide ((C₈H₂₀N)₂MnBr₄) are synthesized via a facile room-temperature evaporation method. C₄H₁₂NMnCl₃ and (C₈H₂₀N)₂MnBr₄ with octahedrally and tetrahedrally coordinated Mn²⁺ have correspondingly exhibited red and green emission peaking at 635 and 515 nm both originating from ⁴T₁–⁶A₁ transition of Mn²⁺ with high photoluminescence quantum yield (PLQY) of 91.8% and 85.1% benefiting from their specific crystal structures. Thanks to their strong photoexcitation under blue light, high PLQY, tunable emission spectra, good environmental stability, the white light-emitting diode based on blending of C₄H₁₂NMnCl₃ and (C₈H₂₀N)₂MnBr₄ delivers an outstanding luminous efficacy of 96 lm W⁻¹, approaching commercial level, and shows no obvious photoluminescence intensity degradation after 3000 h under operation. In addition, manganese halides also demonstrate interesting characteristics under X-ray excitation, C₄H₁₂NMnCl₃ and (C₈H₂₀N)₂MnBr₄ exhibit steady-state X-ray light yields of 50 500 and 24 400 photons MeV⁻¹, low detectable limits of 36.9 and 24.2 nGy_air s⁻¹, good radiation hardness, and X-ray imaging demonstration with high-resolution of 5 lp mm⁻¹. This work presents a new avenue for luminescent Mn-based metal halides toward multifunctional light-emitting applications.