Rare　earth-based　halide　double　perovskites　are　regarded　as　an　emerging　class　of　X-ray　scintillation　materials.　However,　the　majority　of　related　scintillator　applications　are　still　focused　on　single　crystal　and　powder　systems;　the　application　of　nanocrystal　(NC)　scintillators　is　rarely　reported.　Here,　we　present　the　synthesis　of　high-purity　Cs2NaTbCl6　NCs　by　an　improved　hot-injection　method.　Interestingly,　hollow　Cs2NaTbCl6　NCs　are　observed,　the　monitoring　of　the　growth　process　indicates　that　micrometer-sized　NaCl　is　the　initial　product,　and　then　the　NaCl　would　convert　into　Cs2NaTbCl6　NCs　through　the　diffusion　of　Cs+　and　Tb3+　into　NaCl　lattice,　and　the　faster　outward　diffusion　of　Na+　results　in　the　formation　of　hollow　NCs.　The　double　perovskite　NCs　exhibit　green　light　emission,　and　the　photoluminescence　intensity　can　be　significantly　enhanced　through　Ce3+　doping.　In　particular,　the　Cs2NaTbCl6:5%Ce3+　scintillator　exhibits　a　linear　response　and　a　low　detection　limit　of　79.09　nGy/s　when　exposed　to　X-rays.　Furthermore,　a　flexible　scintillator　film　for　X-ray　imaging　is　prepared　by　mixing　NCs　with　polymer,　showing　a　high　spatial　resolution　imaging　capability　of　10　lp/mm.　This　work　provides　a　new　strategy　for　hollow　perovskite　NCs　and　may　shed　light　on　the　synthesis　of　related　hollow　NCs　and　their　applications　in　X-ray　detection.　©　2024　American　Chemical　Society