The　lead-free　Er　3+　-doped　(K　0.48　Na　0.48　Li　0.04　)(Nb　0.96　Bi　0.04　)O　3　(KNLNB-Er-x)　ceramics　were　fabricated　by　conventional　pressureless　sintering.　They　possess　a　tetragonal　perovskite　phase　with　dense　microstructure.　High　transmittances　of　the　ceramics　are　obtained　both　in　the　visible　and　infrared　regions.　The　optical　band　gap　energies　of　them　are　3.07–3.11　eV,　close　to　other　KNN-based　materials.　The　relaxor-like　characteristics,　good　dielectric,　ferroelectric　and　piezoelectric　properties　of　the　ceramics　have　been　obtained.　The　up-conversion　photoluminescence　spectra　have　been　studied　and　obvious　color-tunable　emissions　have　been　observed　by　modulating　temperature.　The　fluorescence　intensity　ratio　(FIR)　value　based　on　green　emissions　at　533　and　555　nm　in　the　temperature　ranging　from　300　to　750　K　have　been　investigated,　giving　the　maximum　sensitivity　of　~　0.0038　K　−1　.　Furthermore,　the　FIR　technique　opens　up　a　method　to　detect　the　Curie　temperature　of　the　ceramics.　Owing　to　both　optical　and　electrical　properties,　the　KNLNB-Er-x　transparent　ceramics　could　be　a　promising　candidate　in　the　application　of　color-tunable　solid-state　lightings,　optical　temperature　sensors,　and　electrical-optical　coupling　devices.　©　2017　Elsevier　Ltd　and　Techna　Group　S.r.l.