Effects of the reaction time and size on the up conversion luminescence of NaYF4:Yb(20%),Er(1%) microcrystals

► The effect of reaction time on the up conversion properties of NaYF4:Yb,Er microprisms is studied. ► The effects of particle size on the up conversion properties of NaYF4:Yb,Er microprisms are studied. ► Hexagonal microprisms with medium size possess a higher emission intensity and Fg/r ratio.