Scintillators　with　high　light　yield,　spatial　resolution,　and　detection　sensitivity　are　desirable　for　X‐ray　imaging.　Howerer,　it　remains　challenging　to　improve　the　light　yield　and　radiation　detection　capability　of　alkali　metal　rare‐earth　fluoride　(ALnF4).　Herein,　a　type　of　Cu2+　ion　heterovalent　co‐doped　LiLuF4:Tb,Cu　microcrystalline　scintillation　material　with　high　light　yield,　persistent,　and　thermostimulated　luminescence　is　obtained　by　defect　engineering.　The　heterovalent　codoping　strategy　not　only　increases　the　radioluminescence　(RL)　intensity,　but　also　introduces　more　carrier　traps　in　the　material　to　enhance　the　long‐afterglow　and　thermoluminescence　intensity　of　LiLuF4:Tb　microcrystals.　After　doping　of　3　mol%　Cu2+　ions,　the　RL　efficiency　is　increased　by　88.61%,　and　the　X‐ray　detection　limit　of　LiLuF4:Tb,Cu　reaches　2.7928　nGy·s‒1.　This　detectivity　is　considerably　lower　than　the　medical　imaging　requirements　(5.5　µGy·s‒1).　Furthermore,　a　large‐area　flexible　scintillation　film　of　dimensions　30 × 30　cm2　is　prepared　to　achieve　high　spatial　resolution　X‐ray　imaging　of　22　LP mm−1@MTF(modulation　transfer　function)　=　0.2.　Besides,　this　flexible　film　enables　X‐ray　imaging　of　curved　objects　and　stores　optical　information　for　＞48 h.　This　work　provides　a　paradigm　for　improving　the　RL　intensity　and　X‐ray　detection　sensitivity　of　alkali　rare‐earth　fluorides　by　crystal　defect　engineering,　and　enriches　X‐ray　high　resolution　extended　imaging　applications.