Eu³⁺ (or Tb³⁺)-doped ZrO₂ nanoparticles with average sizes of 3 ∼ 4 nm were synthesized by us-ing a solvothermal method at 250 ?C. X-ray di?raction (XRD) measurement showed that the crystal structures of the nanoparticles were cubic, tetragonal, and monoclinic phases at room temperature after calcination at 400 ?C, 700 ∼ 900 ?C, and 1200 ?C, respectively. The photoluminescence (PL) the photoluminescence excitation, and the decay curves were measured. From Eu³⁺-doped ZrO₂ nanoparticles, not only the oscillator strength calculated from the lifetime but also the PL intensity obtained from the experiment on the monoclinic phase was found to be 5 ∼ 6 times greater than for the cubic or the tetragonal phase. On the contrary, the PL intensity of Tb³⁺ from Tb³⁺-doped ZrO₂ nanoparticles. Fianlly, dramatically decreased with increasing calcination temperature. PL emitted from Tb³⁺ could not be found in the monoclinic phase.