The　phase　transition　temperature　(e.g.,　that　of　orthorhombic-tetragonal　TO-T)　of　relaxor　ferroelectrics　are　commonly　obtained　through　electrical　method　(i.e.,　temperature　dependence　of　dielectric　constant),　and　the　samples　need　to　be　coated　with　metal　electrode　and　tested　by　a　sophisticated　impedance　analyzer.　This　contact　measuring　method　is　inefficient,　inconvenient　and　easy　to　damage　the　sample　surface,　inapplicable　to　transparent　ferroelectrics.　Here,　we　successfully　fabricated　Bi/Sm　co-doped　K0.5Na0.5NbO3　transparent　ceramics　with　photoluminescent　behavior　and　relaxor-like　ferroelectricity,　which　simultaneously　realized　TO-T　monitoring　and　temperature　sensing　via　fluorescence　intensity　ratio　(FIR)　technology.　This　simple,　rapid,　noncontact　and　nondestructive　optical　way　displays　small　TO-T　deviation　(merely　0.78%)　compared　to　the　electrical　method.　And　the　temperature-dependent　optical　characteristics　and　coercive　electric　field　all　present　abrupt　changes,　whose　abnormal　temperature　regions　are　in　accordance　with　that　around　TO-T.　In　addition,　the　maximum　absolute　sensitivity　and　relative　sensitivity　of　the　ceramics　reach　0.0072　K−1　(at　533　K)　and　0.0111　K−1　(at　453　K),　respectively,　exhibiting　superior　optical　temperature　sensing　performance.　The　tactical　use　of　FIR　technology　is　of　great　significance　for　widening　the　applications　of　luminescent-ferroelectric　transparent　ceramics.　©　2023　The　American　Ceramic　Society.