Ultra-small sized Y2O3:Eu3+ nanocrystals: One-step polyoxometalate-assisted synthesis and their photoluminescence properties

► Y2O3:Eu3+ nanocrystals with narrow size distribution were prepared. ► The sample were highly uniform and dispersed in water solution. ► Y2O3:Eu3+ nanocrystals show stable fluorescence with high quantum yield (about 15%).