UV, Green, and Red Emissions of Cs ₄ PbBr ₆ Investigated by Cathodoluminescence Electron Microscopy

High Resolution Image Download MS PowerPoint Slide We investigated ultraviolet (UV), green, and red emissions observed in Cs 4 PbBr 6 using cathodoluminescence (CL) electron microscopy. Nanoscale CL spectral mapping revealed that the UV and red emissions exhibit uniform intensity distributions over the entire Cs 4 PbBr 6 particle. The temperature-dependent spectral measurements indicate that these UV and red emissions are attributed to localized electronic states such as ions or defect levels, which are homogeneously distributed throughout the entire sample. In particular, the red emission, observable only by high-energy excitation, has a phosphorescence-like component with a long lifetime of tens of seconds, which can be activated by temperature increase. In contrast, the green emission showed granular intensity distributions in the CL mapping. Together with the temperature-dependent spectroscopic and lifetime measurements, it is confirmed that this emission originates from CsPbBr 3 nanocrystals embedded in the matrix. Through assignment of the excitation states, we propose an energy-level diagram of Cs 4 PbBr 6 that accounts for these three distinct emission bands observed in CL.