Solvothermal Synthesis Of CaF₂,SrF₂,BaF₂ Nanocrystals And Study On BaF₂: Yb/Er

In this paper, monodisperse CaF2,SrF2,BaF2,BaF2: Yb/Er nanocrystals with high crystallinity which can be easily dispersed in nonpolar organic solvent (such as cyclohexane and carbon tetrachloride ) were synthesized by solvothermal method under a relatively mild condition. Then i study on BaF2: Yb/Er for the optimum conditions of the synthesis.The structure and morphology of the nanocrystals were characterized by XRD, TEM and HRTEM. The results showed the nanocrystals were rather monodisperse and with a relatively narrow size distribution and high crystallinity. The nanocrystals could be easily dispersed in nonpolar organic solvent (such as cyclohexane and carbon tetrachloride) thus forming transparent colloidal stable solution. The size of CaF2,SrF2,BaF2 nanocrystals was 15 nm,5-7 nm and 10-20 nm, respectively. SrF2 and BaF2 were cubic. CaF2 was hexagonal phase. The selected area electron diffraction (SAED) pattern showed the CaF2,SrF2 and BaF2 were polycrystalline. The inter-planar spacing of the CaF2 was about 0.315 nm, which was identical to the [111] facet distance of bulk CaF2 phase. It grew along the [111] direction. The inter-planar spacing of the SrF2 and BaF2 was 0.29 and 0.310 nm, respectively. Both of them grew along the [200] direction.Using Ba(NO3)2 and BaCl2 as primal materials, respectively. We got Ba2ClF3 when using BaCl2, so the optimum material is nitrate. The products were BaF2 at room temperature, 100°C, 150°C, 180°C, 200°C, but BaF2: Yb/Er nanocrystals obtained at lower than 180°C were nonluminescence. So the appropriate temperature is 180-200°C. Doping Yb/Er with different molar ratio to investigate upconversion luminescence of BaF2: Yb/Er nanocrystals, we obtained the optimum molar ratio of Yb/Er was 6:1. From the Fourier transform infrared spectroscopy of the as-prepared nanocrystals we can clearly see that they were coated with oleic acid molecules. That is why they could be dispersed in nonpolar organic solvent (such as cyclohexane and carbon tetrachloride).We got the monodisperse CaF2,SrF2,BaF2 nanocrystals by solvothermal methods with a simple instrument under a relatively mild condition for the first time. A good result of the upconversion luminescence of BaF2: Yb/Er was achieved also.