Intrinsic Lead Ion Emissions in Zero-Dimensional Cs₄PbBr₆ Nanocrystals

High Resolution Image Download MS PowerPoint Slide We investigate the intrinsic lead ion (Pb 2+ ) emissions in zero-dimensional (0D) perovskite nanocrystals (NCs) using a combination of experimental and theoretical approaches. The temperature-dependent photoluminescence experiments for both “nonemissive” (highly suppressed green emission) and emissive (bright green emission) Cs 4 PbBr 6 NCs show a splitting of emission spectra into high- and low-energy transitions in the ultraviolet (UV) spectral range. In the nonemissive case, we attribute the high-energy UV emission at approximately 350 nm to the allowed optical transition of 3 P 1 to 1 S 0 in Pb 2+ ions and the low-energy UV emission at approximately 400 nm to the charge-transfer state involved in the 0D NC host lattice (D-state). In the emissive Cs 4 PbBr 6 NCs, in addition to the broad UV emission, we demonstrate that energy transfer occurs from Pb 2+ ions to green luminescent centers. The optical phonon modes in Cs 4 PbBr 6 NCs can be assigned to both Pb–Br stretching and rocking motions from density functional theory calculations. Our results address the origin of the dual broadband Pb 2+ ion emissions observed in Cs 4 PbBr 6 NCs and provide insights into the mechanism of ionic exciton–optical phonon interactions in these 0D perovskites.