Novel lead-free double perovskite phosphors of Mn-doped Cs2KBiCl6(Cs2KBiCl6:Mn2+) have been facilely synthesized by using typical hydrothermal method. X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and photoluminescence measurements confirm that the synthesized Cs2KBiCl6:Mn2+phosphors behave double perovskite structure, good morphology, excellent stability, and superior optical properties. An optimal doping concentration of Mn/Bi = 0.4 is achieved in Cs2KBiCl6:Mn2+phosphors, showing maximum photoluminescence quantum yield of 87.2%, lifetime of 0.98 ms, and orange-red fluorescence with the emission peak at 595 nm under UV light excitation. The probable luminescence mechanism could be ascribed to excitation energy transferring from Cs2KBiCl6to Mn, and accordingly contributing to the4T1–6A1transition of the Mn d electron. Superb optical properties provide much room for in-depth fluorescence researches and potential applications of Cs2KBiCl6:Mn2+phosphors.Supplementary InformationThe online version contains supplementary material available at 10.1186/s11671-023-03820-w.