Green-Emitting Powders of Zero-Dimensional Cs(4)PbBr(6): Delineating the Intricacies of the Synthesis and the Origin of Photoluminescence

A detailed investigation into the synthesis of green-emitting powders of Cs(4)PbBr(6) and CsPbBr(3) materials by antisolvent precipitation from CsBr-PbBr(2) precursor solutions in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is reported. Various solvated lead bromide and polybromide species (PbBr(2), [PbBr(3)](−), [PbBr(4)](2−), and possibly [PbBr(5)](3−)or [PbBr(6)](4−)) are detected in the precursor solutions by optical absorbance and emission spectroscopies. The solvodynamic size of the species in solution is strongly solvent-dependent: ~1 nm species were detected in DMSO, while significantly larger species were observed in DMF by dynamic light scattering. The solvodynamic size of the lead bromide species plays a critical role in determining the Cs-Pb-Br composition of the precipitated powders: smaller species favor the precipitation of Cs(4)PbBr(6), while larger species template the formation of CsPbBr(3) under identical experimental conditions. The powders have been characterized by (133)Cs and (207)Pb solid-state nuclear magnetic resonance, and (133)Cs sensitivity toward the different Cs environments within Cs(4)PbBr(6) is demonstrated. Finally, the possible origins of green emission in Cs(4)PbBr(6) samples are discussed. It is proposed that a two-dimensional Cs(2)PbBr(4) inclusion may be responsible for green emission at ~520 nm in addition to the widely acknowledged CsPbBr(3) impurity, although we found no conclusive experimental evidence supporting such claims.