Impurity　doping　is　an　effective　approach　to　tuning　the　optoelectronic　performance　of　host　materials　by　imparting　extrinsic　electronic　channels.　Herein,　a　family　of　lanthanide　(Ln3+)　ions　was　successfully　incorporated　into　a　Bi:Cs2AgInCl6　lead-free　double-perovskite　(DP)　semiconductor,　expanding　the　spectral　range　from　visible　(Vis)　to　near-infrared　(NIR)　and　improving　the　photoluminescence　quantum　yield　(PLQY).　After　multidoping　with　Nd,　Yb,　Er　and　Tm,　Bi/Ln:Cs2AgInCl6　yielded　an　ultrabroadband　continuous　emission　spectrum　with　a　full　width　at　half-maximum　of　~365　nm　originating　from　intrinsic　self-trapped　exciton　recombination　and　abundant　4f–4f　transitions　of　the　Ln3+　dopants.　Steady-state　and　transient-state　spectra　were　used　to　ascertain　the　energy　transfer　and　emissive　processes.　To　avoid　adverse　energy　interactions　between　the　various　Ln3+　ions　in　a　single　DP　host,　a　heterogeneous　architecture　was　designed　to　spatially　confine　different　Ln3+　dopants　via　a　“DP-in-glass　composite”　(DiG)　structure.　This　bottom-up　strategy　endowed　the　prepared　Ln3+-doped　DIG　with　a　high　PLQY　of　40%　(nearly　three　times　as　high　as　that　of　the　multidoped　DP)　and　superior　long-term　stability.　Finally,　a　compact　Vis–NIR　ultrabroadband　(400~2000　nm)　light　source　was　easily　fabricated　by　coupling　the　DiG　with　a　commercial　UV　LED　chip,　and　this　light　source　has　promising　applications　in　nondestructive　spectroscopic　analyses　and　multifunctional　lighting.　©　2022,　The　Author(s).