A dicationic ionic liquid strategy to enhance the thermal stability of manganese bromide scintillators

Conventional organic-inorganic hybrid manganese halides (Mn-OIMHs) as scintillators face challenges in thermal stability. This work proposes a strategy of introducing dicationic ionic liquids (DILs) to construct dicationic Mn-OIMHs with improved thermal stability. Comparative studies for the structures and X-ray scintillation properties are done for a series of Mn-OIMHs, that is, dicationic AMnBr₄ (A = PP214²⁺ (1,4-bis(N-methylpiperidinyl)-butane) for 1, P214²⁺ (1,4-bis(N-methylpyrrolidinium)-butane) for 3, and PP215²⁺ (1,5-bis(N-methylpiperidinyl)-pentane) for 5) and monocationic A₂MnBr₄ (A = PP14⁺ (N-methyl-N-butylpiperidinium) for 2, P14⁺ (N-methyl-N-butylpyrrolidinium) for 4, and PP15⁺ (N-methyl-N-pentylpiperidine) for 6). By leveraging the unique "dual charge centers" to enhance the electrostatic interactions and hydrogen bonding forces, the increased structural rigidity not only improves the photoluminescence quantum yield (PLQY) of materials, but also results in significantly enhanced thermal stability, enabling 1 to maintain 86% of its luminescence intensity at 450 K (vs. 300 K). Furthermore, compared to 2/4/6, the light yield (LY) of 1/3/5 is increased by several fold. Finally, a flexible scintillation film fabricated by embedding 1 in polydimethylsiloxane (PDMS) achieves a spatial resolution of 14.1 lp mm^-1, surpassing that of commercial CsI:Tl detectors (∼10 lp mm^-1). This work provides an effective design strategy for the preparation of Mn-based X-ray scintillators with high thermal stability and excellent photophysical properties.