Ionic Liquid Engineered Defect-Driven Green Emitting Zero-Dimensional Cs₄PbBr₆ Microdisks

Quantum-confined perovskites represent an emerging class of materials with great potential for optoelectronic applications. Specifically, zero-dimensional (0D) perovskites have garnered significant attention for their unique excitonic properties. However, achieving phase-pure, size-tunable 0D perovskite materials and gaining a clear understanding of their photophysical behavior remains challenging. Herein, we report a simple, room-temperature synthesis of phase-pure Cs4PbBr6 microdisks (MDs) via the ionic liquid (IL)-mediated antisolvent precipitation method. By varying the alkyl-chain length, type, and concentration of mono/di- cationic ILs, we have successfully modulated the morphology and optical characteristics of the resulting MDs. Structural characterization through TEM, SAED, PXRD, and EDX confirms the formation of highly crystalline, compositionally pure Cs4PbBr6 MDs. Photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) have revealed strong, intrinsic green emission from the MDs, with no detectable contribution from CsPbBr3 impurities. Moreover, FLIM studies indicate heterogeneity in PL intensity and lifetime, attributed to variations in trap-state distributions across the MDs. Temperature-dependent PL measurements have further substantiated an excitonic PL mechanism, exhibiting a high exciton-binding energy (∼222 meV) and pronounced exciton–phonon coupling. These findings affirm that the green emission originates from defect-mediated midgap recombination within Cs4PbBr6, highlighting the utility of ILs as effective ligands in tuning the morphology and optical response of 0D-perovskites.