Ferroelectric　photo-thermochromic　(PTC)　materials　with　both　high　coloration　contrast　and　high　transparency　have　attracted　great　attention　for　their　applications　in　＇smart　window＇　for　non-contact　optical　information　storage.　Nevertheless,　it　has　been　challenging　to　develop　a　ferroelectric　PTC　material　that　simultaneously　meets　the　distinct　transparency　and　coloration　contrast　requirements.　Herein,　dual　rare-earth　ions　doping　of　1%Er-(K0.5Na0.5)0.985La0.015NbO6　(Er-KNLN)　ferroelectric　ceramics　is　aimed　at　increasing　the　optical　transmittance　and　obtaining　an　ideal　coloration　contrast.　The　traditional　solid-state　reaction　is　exploited　for　ceramics　fabrication,　and　the　optimal　optical　transmittance　(≈70%　at　900 nm)　can　be　obtained　due　to　finer　grains,　more　symmetrical　structure,　and　compact　structure　in　samples　sintered　at　a　suitable　temperature　(such　as　≤1165 °C).　Contributed　from　the　trapping　and　de-trapping　of　charge　carriers　in　vacancy-related　defects,　the　Er-KNLN　ceramics　exhibit　obvious　PTC　behavior　and　the　novel　impedance　modulation　is　developed.　The　coupling　between　PTC　behavior　and　optical　transparency,　lanthanide　up-conversion　emission,　patterned　display,　and　room　temperature　impedance　enables　nondestructive　rewritable　and　readout　characteristics　of　multi-mode　＇0＇　and　＇1＇　states.　This　work　solves　the　main　problems　hampering　the　promising　applications　of　ferroelectric　materials　and　paves　a　way　for　developing　multifunctional　optical　memory　smart　windows.　©　2021　Wiley-VCH　GmbH