Up-convertion (UC) perovskite Er³⁺-doped PbTiO₃ (Er-PTO) nanoparticles with green and red emissions were synthesized via the hydrothermal method. The UC properties were manipulated by adjusting the concentration of Er³⁺ ions dopant. The green emission intensity was decreased as the doping concentration increased from 1% to 4% (mole fraction), whereas the red emission intensity was increased. The influences of Er³⁺ ions on the temperature-sensing performance were further investigated. The results demonstrated that Er-PTO nanoparticles with doping 1% Er³⁺ ions possessed a sensitivity of 3.1 × 10^-3 K^-1 at 475 K, presenting a high potential in optical heating devices.