Structural characterization, vibrational, optical properties and DFT investigation of a new luminescent organic-inorganic material: (C6H14N)3Bi2I9

The new organic-inorganic compound (C6H14N)3Bi2I9 has been grown by the solvent evaporation method. The zero-dimensional (0-D) structure for the bismuth-iodide (C6H14N)3Bi2I9 has been determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group P1c1 and consists of a cyclohexylammonium cations and a discrete (0-D) anion built up of face-sharing bioctahedra which are interconnected by means of hydrogen bonding contacts N-H⋯I. The optimized molecular structure and vibrational spectra were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the LanL2DZ basis set. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out. Optical transmission measurements performed on thin films of (C6H14N)3Bi2I9 revealed three absorption bands at 3.51, 2.91 and 2.46 eV. Photoluminescence measurements showed a peak at around 2.06 eV. The unaided-eye-detectable red luminescence emission comes from the excitonic transition in the Bi2I9 anions.