Fig. 1.

Nanoparticle morphology and spectrum. a–f the TEM images of the NPs with different sizes and surface modification. Scale bar, 200 nm. g the excitation peaks lays on 214 and 308 nm, keeping the emission fixed at 620 nm. h an emission peak of 620 nm was displayed under 214 nm excitation. i emission peaks of 460 nm, 620 nm, and 700 nm were displayed under 308 nm excitation light. j, k the XPS spectrum of Gd (j) and Eu (k) from the Gd₂O₃:Eu-100 NP. l XRD patterns of the Gd₂O₃:Eu-100 NP