The　Er3+　doped　double　perovskite　Ba2CaWO6　crystal　is　a　promising　ratiometric　thermometer　based　on　the　fluorescence　intensity　ratio　(FIR)　of　transitions　from　2H11/2　and　4S3/2　to　the　lowered　4I15/2　level.　However,　the　Ca2+　vacancy　defect　caused　by　the　charge　difference　between　rare-earth　ions　and　the　substituted　alkaline-earth　ions　gives　rise　to　the　non-radiative　probability　and　limits　the　thermal　sensitivity.　Here,　the　up-conversion　luminescence　and　thermometric　performance　of　Er3+,　Yb3+　doped　Ba2CaWO6　are　tuned　by　tri-doping　with　alkaline　ions.　The　Ca2+　vacancy　defect　can　be　eliminated　by　the　introduction　of　Na+,　which　occupies　the　Ca2+　site　when　it　is　doped　into　Ba2CaWO6　with　Er3+　and　Yb3+.　On　the　contrary,　the　doping　of　Cs+　into　Ba2CaWO6　with　Er3+　and　Yb3+　enhances　the　defect　concentration　because　it　occupies　the　site　of　Ba2+.　Thus,　the　tri-doping　of　Na+　reduces　the　non-radiative　probability　and　enhances　the　quantum　efficiency　of　Er3+,　leading　to　the　improvement　of　the　thermometric　sensitivity　of　Ba2CaWO6.　As　a　result,　we　get　an　excellent　thermometric　Ba2CaWO6:8%Yb3+,3.5%Er3+,6%Na+　powder　with　a　luminescence　lifetime　of　515　μs　and　maximum　thermal　sensitivity　(Sr)　of　1.45%/K,　which　is　more　than　three　times　higher　than　that　of　the　BCWO:Er3+　powder.　©　2022　Chinese　Society　of　Rare　Earths