In this work, (1Àx)(K 0.48 Na 0.52 )(Nb 0.95 Sb 0.05 )O 3Àx ÀxEr 0.5 (Na 0.82 K 0.18 ) 0.5 ZrO 3 (x = 0-0.05) ceramics were fabricated by solid-state reaction techniques. The rhombohedral-tetragonal (R-T) phase boundary of the ceramics was identified at 0.04 £ x, thus providing an opportunity to investigate the upconversion emission derived from the Er 3+ ions at the R-T phase boundary. Under 980 nm laser excitation, the R-T phase ceramics exhibited a strong green emission. In addition, the fluorescence intensity ratios of green emissions at 530 nm and 550 nm were investigated in a temperature range of 180-510 K, and maximum sensing sensitivity was found to be 0.0037 K À1 . The results indicate that Er 3+ -doped ceramics with R-T phase boundaries can be applied to new multifunctional electro-optical temperature sensors. Laser excitation heating effects were also observed in detail.