Lead-free　bismuth-based　halide　perovskites　and　their　analogues　have　attracted　research　interest　for　their　high　stability　and　optoelectronic　properties.　However,　the　morphology-controlled　synthesis　of　bismuth-based　perovskite　nanocrystals　has　been　rarely　demonstrated.　Herein,　we　report　the　colloidal　synthesis　of　zero-dimensional　(0D)　Cs3BiCl6　nanosheets　(NSs),　Cs3Bi2Cl9　NSs/nanoplates　(NPs)　and　Cs4MnBi2Cl12　NPs　through　a　hot-injection　method.　We　demonstrate　that　the　Cs3BiCl6　NSs,　as　an　initial　product　of　Cs3Bi2Cl9　and　Cs4MnBi2Cl12　NPs,　can　transform　into　Cs3Bi2Cl9　NSs　or　Cs4MnBi2Cl12　NPs　via　Cl-induced　metal　ion　insertion　reactions　under　the　templating　effect　of　Cs3BiCl6.　This　growth　mechanism　is　also　applicable　for　the　synthesis　of　Cs4CdBi2Cl12　nanoplates.　Furthermore,　the　alloying　of　Cd2+　into　Cs4MnBi2Cl12　lattice　could　weaken　the　strong　coupling　effect　between　Mn　and　Mn,　which　leads　to　a　prolonged　photoluminescence　lifetime　and　an　enhanced　photoluminescence　quantum　yield　(PLQY).　As　a　proof　of　concept,　the　alloyed　Cs4MnxCd1-xBi2Cl12　NPs　are　used　as　a　scintillator,　which　show　a　lowest　detection　limit　of　134.5　nGy/s.　The　X-ray　imaging　results　display　a　high　spatial　resolution　of　over　20　line　pairs　per　millimeter　(lp/mm).　These　results　provide　new　insights　in　the　synthesis　of　anisotropic　bismuth-based　perovskite　nanocrystals　and　their　applications　in　radiation　detection.