Whether or Not Emission of Cs4PbBr6 Nanocrystals: High-Pressure Experimental Evidence

The origin of green emission in the zero-dimensional (0D) perovskite Cs4PbBr6 nanocrystals (NCs) remains a considerable debate. Herein, an approach involving a combination of high-pressure experiments and theoretical simulation was employed to elucidate the controversial origin of photoluminescence from emissive Cs4PbBr6 NCs (E416). Results obtained from first-principles density functional theory (DFT) calculations, as implemented in the Vienna ab initio simulation package codes, implied that the photoluminescence energies from bromine vacancy decreased persistently with pressure. Experimentally, the photoluminescence energies tended to decrease in the low-pressure region, followed by an increase beyond similar to 1.4 GPa. While the emergent disagreement between the first-principles calculation and highpressure experiment excludes the possibility of vacancy-tuning, the consistent change observed in the pressure-dependent emission between E416 and CsPbBr3 NCs offered a reliable interpretation for the occurrence of green emission from a CsPbBr3 impurity embedded in the Cs4PbBr6 matrix. Further comprehensive analysis demonstrated that the strong green emission of E416 NCs originated from the impurity CsPbBr3 NCs embedded in Cs4PbBr6 matrix. Our study represents a significant step forward to a deeper understanding of the emissive origins of Cs4PbBr6 NCs and promotes the application of this novel strategy in light-emitting devices.