Organic　fluorescence　scintillators,　owing　to　the　ultrafast　response　time,　versatile　chemical　structures,　low　processing　temperature,　and　low　cost,　are　considered　as　one　of　the　promising　materials　for　medical　diagnostics,　radiation　detection,　and　X-ray　astronomy.　However,　the　low　radioluminescence　(RL)　intensity　and　low　sensitivity　hinder　their　practical　applications.　In　this　work,　a　highly　efficient　organic　fluorescent　scintillator,　4,4′-bis(9-carbazolyl)biphenyl　(CBP),　is　presented,　exhibiting　a　high　X-ray　RL　intensity,　narrow　full　width　at　half-maximum　of　49　nm,　and　ultrafast　decay　time　of　1.15　ns.　More　importantly,　it　has　a　low　detection　limit　of　25.5　nGy　s−1,　which　is　only　1/215　dose　rate　compared　with　the　commercial　X-ray　diagnostics.　Such　an　excellent　scintillation　performance　is　mainly　attributed　to　its　high　photoluminescence　quantum　yield　(PLQY　=　61.92%)　and　good　carrier　transport　(average　hole　mobility　of　0.094　cm2　V−1　s−1).　By　mixing　the　CBP　into　polydimethylsiloxane,　the　fabricated　large　area　flexible　film　can　be　applied　in　X-ray　radiography,　which　exhibits　a　high　spatial　resolution　of　14.3　lp　mm−1　at　MTF　＞　0.2.　This　work　paves　a　way　for　the　implementation　of　organic　fluorescence　dyes　with　high　PLQY,　high　carrier　mobility　in　efficient　X-ray　scintillation　and　imaging.　©　2023　Wiley-VCH　GmbH.