Abstract: Y₂O₃ ∶Er,Yb nanocrystals were synthesized by the reverse microemulsion under hydrothermal treatmentwhich became high luminescent Y₂O₃ ∶Er,Yb upconversion nanocrystals via calcination at a certain temperature. Compared with nanocrystals prepared by reverse microemulsion, the enhancement of upconversion luminescent emission was observed. The hydrothermal treatment improved the crystallinety of the nanocrystals which favored the population of electron on the ^{4F_9/2 level of Er ion. This led to the enhancement of the red emission.}

Key words: Y₂O₃, nanocrystals, upconversion