Luminescent　metal　halides　doped　with　ns2-metal　ions　such　as　6s2-metal　Bi3+　have　aroused　reviving　interest　owing　to　their　outstanding　optical　properties;　however,　the　origin　of　the　photoluminescence　(PL)　remains　controversial　and　unclear.　Herein,　we　report　a　strategy　for　the　controlled　synthesis　of　Bi3+-doped　vacancy-ordered　double　perovskite　Cs2SnCl6　nanocrystals　(NCs)　and　unravel　the　triplet　excited-state　dynamics　of　Bi3+　through　temperature-dependent　PL　and　ultrafast　femtosecond　transient　absorption　spectroscopies.　Owing　to　the　aliovalent　Bi3+　doping　in　the　spatially　confined　zero-dimensional　(0D)　structure　of　Cs2SnCl6,　Bi3+　ions　experience　an　enhancive　Jahn-Teller　distortion　in　the　excited　state,　which　results　in　intense　broadband　blue　PL　originating　from　the　inter-configurational　3P0,1　→　1S0　transitions　of　Bi3+　at　450　nm,　with　a　large　Stokes　shift　and　a　quantum　yield　of　35.2%.　Specifically,　an　unusual　thermal-enhanced　Jahn-Teller　splitting　of　the　excitation　band　and　a　remarkable　transition　of　the　PL　lifetime　from　ms　at　10　K　to　µs　at　300　K　were　observed,　as　solid　evidence　for　the　isolated　Bi3+　emission.　These　findings　clarify　the　controversy　about　the　PL　origin　in　ns2-metal　ion-doped　lead-free　luminescent　metal　halides,　thereby　paving　the　way　for　exploring　their　optoelectronic　applications.　[Figure　not　available:　see　fulltext.].　©　2022,　Tsinghua　University　Press.