In　this　work,　two　spiro-type　compounds　are　investigated　with　similar　molecular　structure　and　stacking　structure.　By　simply　altering　the　acceptor＇s　heteroatoms,　a　strategy　to　enhance　room　temperature　phosphorescence　(RTP)　performance　is　presented.　The　intersystem　crossing　process　can　effectively　be　accelerated　by　reducing　the　energy　gap　between　the　singlet　and　triplet　states　(Delta　E-ST)　through　adjusting　the　molecular　energy　level.　Besides,　thermally　activated　delayed　fluorescence　(TADF)　is　emerging　in　dilute　solution　due　to　such　small　Delta　E-ST.　This　is　helpful　for　deeply　understanding　the　mechanism　of　competition　in　different　radiative　decay　pathways　(RTP　and　TADF).