Currently,　lanthanide　(Ln3+)　doped　Pb‐free　double　perovskites　(DPs)　suffer　from　competitive　emissions　of　the　self‐trapped　exciton　(STE)　and　Ln3+.　Herein,　a　new　type　of　Nd3+‐doped　Cs2AgInCl6　DPs　with　Na+/Bi3+　co‐alloying　is　developed.　Benefiting　from　Na+/Bi3+‐induced　local　structural　modification,　both　STE　broadband　visible　luminescence　and　Nd3+　near‐infrared　(NIR)　emissions　are　boosted　via　free　exciton　sensitization.　Specifically,　a　total　648‐fold　enhancement　in　emitting　intensities　compared　to　the　Na+/Bi3+‐free　counterpart　is　realized,　with　a　significantly　improved　NIR　photoluminescence　quantum　yield　(PLQY)　from　0.16%　to　30.3%.　First‐principles　density　functional　theory　calculations,　Raman　spectra,　and　steady/transient‐state　PL　spectra　verify　the　modification　of　local　site　symmetry,　breakdown　of　parity‐forbidden　absorption,　and　reduction　of　electron‐phonon　coupling　via　Na+/Bi3+　doping.　Finally,　a　compact　vis–NIR　broadband　light‐emitting　diode　(LED)　is　designed　by　coupling　the　Na/Bi/Nd:　Cs2AgInCl6　DP　with　a　commercial　ultraviolet　LED　chip,　which　shows　promising　applications　in　spectroscopic　analyses　and　multifunctional　lighting.