Sodium Controlled Synthesis of Hexagonal-Phase NaGdF4:Yb,Er Nanocrystals with Enhanced Upconversion Fluorescence for Bioimaging

摘要

In this study, we demonstrate a Na+ induced cubic-to-hexagonal phase transition in NaGdF4 nanocrystals. Based on such mechanism, a convenient method has been established to synthesize water-soluble and hexagonal-phase NaGdF4 nanocrystals by employing excess Na+ ions in the ethylene glycol solvent. By co-doping Yb, Er or Yb, Tm ions, the synthesized NaGdF4:Yb, Er and NaGdF4:Yb, Tm nanocrystals exhibit bright upconversion fluorescence upon 980 nm diode laser excitation. This strategy will facilitate the synthesis of hexagonal phase lanthanide-doped NaGdF4 nanocrystals with good biocompatibility for bioimaging applications.