Solvothermal synthesis and upconversion spectroscopy of monophase hexagonal NaYF4:Yb3+/Er3+ nanosized crystallines

The synthesis of single-phase hexagonal NaYF4:Yb3+/Er3+ upconversion phosphors was investigated by a facile solvothermal processing. It was found that solvents adopted could influence the phase composition, morphology and luminescence property of resultant NaYF4 nanosized crystals greatly. When a mixture of oleic acid–glycol–ethanol was used as solvent, the monophase hexagonal NaYF4:Yb3+/Er3+ nanocrystals were successfully obtained, which exhibited nanorods morphology with a longitude of about 200 nm and a diameter of 50–80 nm. By co-doping Yb3+ and Er3+, hexagonal NaYF4 nanorods emitted bright upconversion luminescence at 530 nm and 652 nm under excitation of 980 nm, which was much superior than those of NaYF4:Yb3+/Er3+ particles synthesized in other solvents such as deionized water, ethanol, glycol and oleic acid.

► Oleic acid–glycol–ethanol as solvent enables growth of hexagonal NaYF4:Yb3+/Er3+ nanorods.
► Different solvents adopted have great effects on the structure and morphology of NaYF4.
► Solvents with high viscosity value can promote the hexagonal NaYF4 nanocrystallines.
► Well crystallized particles are benefit for high luminous intensity.