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

Abstract

A luminescent zero-dimensional organic–inorganic hybrid indium halide (TUH)6[In1–x Sb x Br6]Br3 (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–H···Br and N–H···S 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–x Sb x Br6]Br3 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–x Sb x Br6]Br3 compounds in the field of photonics.