The　efficient　production　of　high-quality　scintillators　with　long　radioluminescence　afterglow　is　crucial　for　high-performance　X-ray　luminescence　extension　imaging.　However,　scaling-up　the　synthesis　of　ligand-free　scintillators　to　fabricate　large-area　X-ray　imaging　screens　for　industrial　applications　remains　a　challenge.　In　this　study,　we　report　an　efficient　method　to　synthesize　ligand-free,　lanthanide-doped　microscintillators　by　a　one-pot　reaction　via　the　concentrated　hydrothermal　method.　The　as-synthesized　microscintillators　exhibit　prolonged　persistent　radioluminescence　for　up　to　30　days　after　X-ray　exposure　and　remain　high　stability　in　air　or　water　for　more　than　18　months　without　deterioration.　Monte　Carlo　simulations　indicate　that　the　size　effect　is　responsible　for　the　excellent　afterglow　performance　of　the　microscintillators.　We　employ　these　high-quality　lanthanide-doped　microscintillators　to　fabricate　a　large-area　X-ray　imaging　detector　using　a　blade-coating　method,　a　spatial　resolution　of　24.9　lp/mm　for　X-ray　imaging.　Our　study　offers　a　solution　for　scaling-up　the　synthesis　of　low-cost　microscintillators　for　practical　applications.