Abstract Lanthanide (Ln)-based metal halides with excellent luminescence properties, large Stokes shifts, and low toxicity have aroused wide attention as scintillators for X-ray imaging. However, the lack of fast and mild synthesis methods of Ln-based metal halides, as one of the technical challenges, limits their applications. Here, benefiting from the innovative selection of methanol and ethanol as the solvent and anti-solvent, respectively, a series of Cs3LnCl6 (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) microcrystals (MCs) were prepared via the recrystallization method at room temperature for the first time. This recrystallization method could also realize large-scale production at one time and recyclable recrystallization of single-element MCs and the preparation of high-entropy five-element Cs3{TbDyHoErTm}1Cl6 crystals. Among these Cs3LnCl6 MCs, Cs3TbCl6 MCs with 4f → 5d absorption transition possess the highest photoluminescence quantum yield of 90.8%. Besides, under X-ray irradiation, Cs3TbCl6 MCs show a high light yield of ~51,800 photons MeV−1 and the as-fabricated thin films possess promising X-ray imaging ability and excellent spatial resolutions (12 lp mm−1). This work provides a new method for ultrafast preparing Ln-based metal halides under mild synthetic conditions and highlights their excellent potential as scintillators for X-ray imaging.