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

Abstract

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 is 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, PP215²⁺ (1,5-bis(N-methylpiperidinyl)-pentane) for 5) and monocationic A₂MnBr₄ (A = PP14⁺ (N-methyl-Nbutylpiperidinium) for 2, P14⁺ (N-methyl-N-butylpyrrolidinium) for 4, 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 maintaining 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, surpassing that of commercial CsI: Tl detectors (~10 lp/mm). This work provides an effective design strategy for the preparation of Mn-based X-ray scintillators with high thermal stability and excellent photophysical properties.