Tunable CsPbBr3/Cs4PbBr6 phase transformation and their optical spectroscopic propertiesElectronic supplementary information (ESI) available: Table S1 and Fig. S1-S6. Experimental details, the evaluated lifetimes, PLQYs, XRD patterns, temperature-dependent PL spectra, decay curves spectra, FTIR as well as PL images. See DOI: 10.1039/c8dt00430g

As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs 4 PbBr 6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr 3 and zero-dimensional Cs 4 PbBr 6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs 4 PbBr 6 and CsPbBr 3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs 4 PbBr 6 is much longer than that of CsPbBr 3 , and photo-blinking is easily detected in the Cs 4 PbBr 6 product, proving that the zero-dimensional Cs 4 PbBr 6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs 4 PbX 6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr 3 /Cs 4 PbBr 6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs 4 PbX 6 products. As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics.