Luminescent Zero-Dimensional Hybrid Lead Thiohalide Nanostructures for High Quantum Yield and Broadband Excitation
Luminescent trans-[Pb(DMTU-S)4Cl2] (DMTU: N,N′-dimethylthiourea) was designed and prepared via either mechanochemical or solvothermal methods, and the structures of DMTU and trans-[Pb(DMTU-S)4Cl2] have been resolved using X-ray single-crystal diffraction. Upon excitation over broadband covering the range from 450 to 250 nm, trans-[Pb(DMTU-S)4Cl2] shows yellow-green emission peaking at 549 nm with a spectral width of 110 nm, which is assigned to the triplet–singlet transition of Pb2+ ions within distorted heterogeneous S4Cl2 octahedra. The broadband excitation comprised singlet–singlet transitions of Pb2+ ions and energy transfer from orbitals involving those of organic ligands. Simultaneous analysis of the luminescent bandwidth and Stokes shift gives for Pb2+ ions in S4Cl2 octahedra the value of the Huang–Rhys parameter S = 4.25 and the energy of phonon involved in the formation of the luminescence spectrum of the order of 90 meV. Quantum yield as high as 91% is detected for excitation at 365 nm. This high quantum yield indicates the absence of noticeable concentration quenching at an average distance of 9.4 Å between the Pb2+ ions within the structure of trans-[Pb(DMTU)4Cl2]. The weak spin–orbit intersystem crossing is deduced from a high photoluminescence quantum yield (PLQY) value. Time dependent-density functional theory (TD-DFT) calculations of the nanocluster indicate the red shift of absorption bands in Pb(DMTU)4Cl2 with respect to parent DMTU. The high-performance photoluminescence and stability demonstrated promising applications in photonics.