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In this report, we present a new approach for the fabrication and application of Cs4PbBr6 microcrystals (Cs4PbBr6 MCs). The Cs4PbBr6 MCs are synthesized via an anti-solvent induced crystallization of PbBr2:CsBr directly in dimethylsulfoxide (DMSO) by introducing HBr (HBr, 48% aqueous solution). The ratio of HBr and DMSO plays a vital role in the formation of Cs4PbBr6. By controlling the HBr/DMSO ratio, pure Cs4PbBr6 or the CsPbBr3 phase can be obtained. The Cs4PbBr6 MCs were initially obtained by adding HBr to CsBr:PbBr2/DMSO. However, on increasing the amount of the added HBr, Cs4PbBr6 MCs were converted to CsPbBr3 MCs and the photoluminescence (PL) disappeared. It was also found that CsPbBr3 MCs can be transformed to Cs4PbBr6 MCs by simply adding DMSO to the dried CsPbBr3 MCs. The Cs4PbBr6 MCs exhibit a strong PL at 516 nm with a full width at half-maximum of 25 nm regardless of the crystal size (5–10 μm). On using Cs4PbBr6 MCs as a light converter in ultraviolet light emitting diodes, a PL intensity th...