Microwave-assisted synthesis and upconversion luminescence of NaYF4:Yb, Gd, Er and NaYF4:Yb, Gd, Tm nanorods

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles are emerging as potential candidate in diverse areas, ranging from biomedical imaging to photonics. Here, we develop a facile strategy to synthesize NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods via microwave synthesis route by controlling the synthesis time and compared the optical properties similar nanorods prepared via solvothermal technique. With the increase in synthesis time, the phase of the particle found to change from mixed phase to purely hexagonal and morphology of the particles change mixed phase of spherical and rod-shaped particles to completely nanorods for a synthesis time of 60 min. Further, the intrinsically hydrophobic particles changed to hydrophilic by removal of oleic capping via acid treatment and the amine functionalized silica coating. The upconversion luminescence as well as laser power dependent emission properties of the surface modified particles elucidate that surface modification route influence the upconversion luminescence as well as solvent dependent emission properties. Moreover, the laser power dependent studies elucidate that the upconversion process in a multi-photon process.

Automated summary

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles have great potential in various fields, and a facile strategy to synthesize the particles was developed in this study. By controlling the synthesis time, NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods were successfully synthesized via microwave synthesis route, and their optical properties were compared with those prepared via solvothermal technique. The phase and morphology of the particles were found to change with the increase in synthesis time. Surface modification of the particles transformed their hydrophobicity to hydrophilicity, and the surface modification route influenced the upconversion luminescence and solvent-dependent emission properties. Furthermore, the laser power dependent studies revealed that the upconversion process is a multi-photon process.