Bandgap Narrowing in Europium(II)-Based Bromide Hybrids toward Improved X-ray Scintillation and Imaging

Chemical design of luminescent metal halides as high-performance X-ray scintillators is in urgent demand. Herein, rare earth Eu(II) was innovated as a B-site cation to create brand-new metal halide scintillators, and a regulating bandgap was further developed via organic molecule design based on the same anionic chain of [EuBr 3 MeOH] n n –, namely, [Cat]EuBr 3 MeOH [Cat = 1-butyl-1-methylpiperidinium (PP14), 1-propyl-1-methylpiperidinium (PP13), and 1-ethyl-3-methylimidazolium (Emim)]. Owing to the smaller bandgap of [Emim]Br, [Emim]EuBr 3 MeOH possesses an enhanced light yield of 43,000 ± 100 ph MeV –1 as scintillators. The conjugated attribute of Emim + also contributes to π–π stacking, resulting in a more rigid structure, reducing the nonradiative transition. The scintillator film by using [Emim]EuBr 3 MeOH emanates spatial resolution above 10 lp mm –1 . This study provides a design principle by B-site cations screening and bandgap engineering of organic cations for enhancing the light yield property and exemplifies novel materials in the family of Eu(II) halide hybrids as potential scintillators.