Abstract: x(Yb)=18%，x(Er)=2% codoped α-NaYF₄, α-NaLuF₄,β-NaYF₄,β-NaLuF₄4 and LiYF₄ nanocrystals were synthesized by using high temperature thermal decomposition method. X\|ray diffraction (XRD)， transmission electron microscopy (TEM) and photoluminescence spectroscopy were used to characterize the crystal structure， morphology and luminescence properties of the samples. The results show that all as-prepared samples are pure phase. The  size distribution of the as-prepared samples with a nearly spherical shape is about 10—15 nm.    The as-prepared samples exhibit emission at around 1 550 nm under the excitation of 980 nm  laser. Among them， β-NaLuF₄∶Yb,Er has the strongest emission at the around of 1 550 nm.

Key words:  ytterbium/erbium; , fluoride; , nanocrystal; , near infrared; , downconversion