X-ray scintillation and photoluminescence of isomorphic ionic bismuth halides with [Amim]+ or [Ammim]+ cations

Three isomorphic ionic bismuth(III) halides were synthesized, utilizing 2,2′-bipyridyl-1,1′-dioxide (bp2do) as the organic ligand decorated on the halobismuthate(III) moieties, namely, [Ammim][BiBr4(bp2do)] (1, Ammim = 1-allyl-2,3-dimethylimidazolium), [Ammim][BiCl4(bp2do)] (2) and [Amim][BiCl4(bp2do)] (3, Amim = 1-allyl-3-methylimidazolium). They all crystallize in the space group of Pca21 with a similar supramolecular packing mode. However, the average adjacent Bi–Bi distances are slightly different, that is 1 > 2 > 3. Moreover, they possess different phosphorescence quantum yields (QYs) with 0.38% for 1, 27.83% for 2 and 34.76% for 3. Note that the QY of 3 remains the highest for bp2do-based halobismuthate hybrids. Their phosphorescence originates from the organic ligand bp2do, in which an inorganic-to-organic charge transfer (IOCT) process exists, as confirmed by density functional theory (DFT) calculations. The three compounds possess X-ray scintillation properties. Eventually, a WLED could be fabricated by mixing commercial nitride red phosphor with cyan-emitting 3. This study provides a method for the synthesis of organic ligand based ionic bismuth halide hybrids with higher QYs, and enriches X-ray scintillation materials.