Hexadecylpyridinium Chloride Mediated Hydrothermal Synthesis of NaYF4:Yb, Er Nanocrystal and Their Luminescent Properties

Upconversion nanocrystals with uniform size and hydrophilic surface have potential applications in biological medical engineering. In this study, hydrophilic NaYF4:Yb, Er nanospheres were synthesized via hexadecylpyridinium chloride (CPC) mediated hydrothermal process. The synthesized NaYF4:Yb, Er upconversion nanospheres (UCNSs) were characterized by various characterization methods. Results showed that the synthesized UCNSs exhibited a uniform sphere-like structure with average diameter of ~250 nm. The surface of UCNSs was captured by CPC molecule indicating hydrophilic properties of UCNSs. The spherical UCNSs composed of mixed phase (α+β) NaYF4 nanocrystals. This is the novel study for synthesis of NaYF4:Ln3+ crystal employing CPC as ligand. Moreover, the effect of CPC concentration on synthesis of UCNSs was investigated by comparatively studying morphology, crystal phase and luminescent properties of desired sample prepared under different experimental conditions. It was found that high concentrations of CPC ligands were more favorable for forming NaYF4 crystal nanospheres with morphology that is more regular, have smoother surface, with higher crystallinity and better upconversion fluorescent properties. The possible growing mechanism was proposed and growing of NaYF4:Yb, Er nanospheres followed the classical Ostwald ripening process.