Green-Emitting Powders of Zero-Dimensional Cs₄PbBr₆: Delineating the Intricacies of the Synthesis and the Origin of Photoluminescence

Abstract

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.

Lead-Halide Scalar Couplings in 207Pb NMR of APbX3 Perovskites (A = Cs, Methylammonium, Formamidinium; X = Cl, Br, I)

“…Of fundamental importance are the first observations of lead-halide J-coupling in MAPbCl 3 ( 1 J Pb-Cl ) and in CsPbBr 3 as well as Cs 4 PbBr 6 27,32 . J-couplings are mediated through bonds by hyperfine interactions between the nuclei and their local electrons.…”

Exciton Relaxation Dynamics in Perovskite Cs4PbBr6 Nanocrystals

“…Various research groups have described the origin of PL emission from Cs 4 PbBr 6 crystals in different ways. 23 , 24 Ray et al proposed that the green emission appeared from the formation of impurities in the Cs 4 PbBr 6 crystals. Jung et al theoretically explained that the green emission originated from the native defect states.…”

Laser-Assisted Fabrication for Metal Halide Perovskite-2D Nanoconjugates: Control on the Nanocrystal Density and Morphology

“…In the second explanation, this emission was attributed to point-defects emission originating from the intrinsic features or bromide vacancies [33] in the non-fluorescent 0D perovskite structure [34]. Our indication is the first experimental observation that the strong photoluminescence of the Cs 4 PbBr 6 nanohexagons arises from the inclusion of a fluorescent phase in a non-fluorescent similar to that observed in green emitting Cs 4 PbBr 6 powders [35] or due to synergetic effects at CsPbBr 3 -Cs 4 PbBr 6 interfaces [36].…”