The　intense　2.9　mu　m　MIR　(mid-infrared)　luminescence　corresponding　to　the　Dy3+:　H-6(13/2　)-＞　H-6(15/2)　transition　was　achieved　for　the　first　time　in　Dy3+/Yb3+　ions　co-doped　SrF2　crystals.　2　at%　Dy3+:　SrF2,　2　at%　Dy3+/5　at%　Yb3+:　SrF2,　and　5　at%　Yb3+:　SrF2　crystals　were　grown　by　Bridgman　method.　The　influence　of　Yb3+　on　its　spectral　properties　and　energy　transfer　mechanisms　has　been　studied.　In　comparison　to　Dy3+　doped　SrF2　crystals,　Dy3+/Yb3+　co-doped　crystals　exhibit　not　only　intense　2.9　mu　m　emission　but　also　longer　high　laser　energy　level　lifetimes,　favoring　2.9　mu　m　population　inversion　and　lasing　behavior.　Furthermore,　the　ET　efficiency　from　Yb3+　to　Dy3+　in　Dy3+/Yb3+　co-doped　crystals　is　found　to　be　as　high　as　95.34%,　indicating　that　the　ET　from　Yb3+　is　efficient.　The　results　show　that　incorporating　Yb3+　into　Dy3+:　SrF2　crystals　improves　the　ability　to　achieve　2.9　mu　m　lasing　action,　which　could　be　used　as　a　potential　gain　media　for　laser　diode-pumped　MIR　lasers.　(C)　2022　Elsevier　B.V.　All　rights　reserved.