Fig. 7From: Synthesis and Luminescence Properties of Water Soluble α-NaGdF4/β-NaYF4:Yb,Er Core–Shell NanoparticlesUC luminescence spectra of the as-prepared heterogeneous core/shell α-NaGdF4/β-NaYF4:Yb,Er crystals with varied reaction time (black: 2 h, red: 6 h, green: 12 h, blue: 24 h) excited by 980-nm infrared light. (Inset: Local magnified patterns of UC spectra in the region of 265–330 nm, in which the characteristic peaks of Gd3+ were observed)Back to article page