Yellow-Orange Emission in Sb³⁺-Doped Hexakis(thiocarbamidium) Hexabromoindium(III) Tribromide

A luminescent zero-dimensional organic-inorganic hybrid indium halide (TUH)(6)[In1-xSbxBr6]Br-3 (TU = thiourea, 0 <= x <= 0.0998) was synthesized via the solvothermal method. In structures, resolved by single-crystal X-ray diffraction, isolated distorted [InBr6](3-) and [SbBr6](3-) octahedra are linked to organic TUH+ cations by intermolecular N-HBr and N-HS hydrogen bonds. The crystals were characterized by elemental analysis, TG-DSC, powder X-ray diffraction, FTIR analysis, and steady-state absorption and photoluminescence spectroscopy. (TUH)(6)[In1-xSbxBr6]Br-3 exhibits a broadband yellow-orange emission centered at 595-602 nm with a half-width of 141-149 nm (0.48-0.52 eV) and a large Stokes shift of 232-238 nm (1.33-1.35 eV). This emission can be attributed to the self-trapped exciton emission of triplet states of the octahedral anion [SbBr6](3-) or [InBr6](3-). Two possible emission mechanisms were discussed. Doping with Sb3+ leads to a significant increase in photoluminescence quantum yield from 25.7 at x = 0 to 48.4% at x = 0.0065, when excited at 365 nm, indicating the potential use of (TUH)(6)[In1-xSbxBr6]Br-3 compounds in the field of photonics.