Pure zero-dimensional Cs₄PbBr₆ single crystal rhombohedral microdisks with high luminescence and stability

Zero-dimensional (0D) perovskite Cs₄PbBr₆ has been speculated to be an efficient solid-state emitter, exhibiting strong luminescense on achieving quantum confinement. Although several groups have reported strong green luminescence from Cs₄PbBr₆ powders and nanocrystals, doubts that the origin of luminescence comes from Cs₄PbBr₆ itself or CsPbBr₃ impurities have been a point of controversy in recent investigations. Herein, we developed a facile one-step solution self-assembly method to synthesize pure zero-dimensional rhombohedral Cs₄PbBr₆ micro-disks (MDs) with a high PLQY of 52% ± 5% and photoluminescence full-width at half maximum (FWHM) of 16.8 nm. The obtained rhombohedral MDs were high quality single-crystalline as demonstrated by XRD and SAED patterns. We demonstrated that Cs₄PbBr₆ MDs and CsPbBr₃ MDs were phase-separated from each other and the strong green emission comes from Cs₄PbBr₆. Power and temperature dependence spectra evidenced that the observed strong green luminescence of pure Cs₄PbBr₆ MDs originated from direct exciton recombination in the isolated octahedra with a large binding energy of 303.9 meV. Significantly, isolated PbBr₆^4- octahedra separated by a Cs⁺ ion insert in the crystal lattice is beneficial to maintaining the structural stability, depicting superior thermal and anion exchange stability. Our study provides an efficient approach to obtain high quality single-crystalline Cs₄PbBr₆ MDs with highly efficient luminescence and stability for further optoelectronic applications.