Up-conversion luminescence and optical temperature sensing of Er3+, Yb3+ co-doped Gd2O3 phosphors with different F-/Ln3+

•The process of grain forming self-assembled structure was revealed.•The morphology and up-conversion luminescence intensity of the phosphors are regulated by controlling the content of NH4F.•The absolute sensitivity of optical temperature sensing is improved through the florescence intensity ratio based on Stark sublevels.•Materials shows excellent luminescence properties and high absolute sensitivity, applicable in optical temperature sensing.