The synthesis of Nd3＋,Y3＋：CaF2 nanopowder was conducted by azeotropic distillation method,which effectively dehydrated hydrous CaF2 and prevented forming hard agglomerates.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,scanning calorimetries-thermalgravimetry（DSC-TG）,Fourier transform infrared spectroscopy（FT-IR） and absorption spectroscopy were performed to characterize the powder properties.The experimental results showed that products obtained by azeotropic distillation were single phased,rather monodispersed,successfully prevented the hard agglomerate formation and effectively removed the residual water inside the as-prepared precipitate than that of the direct drying.The absorption spectra showed a wider and stronger absorption bands around 792 nm,which should be profitable for LD pumping.
The aim of this work was to prepare MgF2 translucent ceramic by using nanopowders as raw materials and to study its properties.The MgF2 nanopowders were prepared using chemical precipitation and the translucent ceramics were fabricated by hot-pressing sintering in a vacuum environment. X-ray diffraction analysis showed that the powders were homogeneous with an average particles size about 13 nm. By comparing the results of transmission electron microscopy, it could be concluded that the porous structure of precursor powders could be improved by calcination. The SEM images of MgF2 indicated that the as-prepared ceramics were well densified at 900 ℃. The photo of the ceramic sample showed that high translucence is a main breakthrough in the field of MgF2 materials preparation. For the translucent ceramic sample sintered at 900 ℃, the Viekers hardness and density were 5.55 GPa and 98.74%, respectively, and its highest transmittance with thickness of lmm reached 87% in the wavelength from 2.5 lain to 10 btm, all which made it advantageous to be a kind of infrared windows and dome materials.
The effects of different sintering addictives on the preparation of CaF2 transparent ceramics were studied. Transparent CaF2 ceramics were fabricated by vacuum sintering and hot isostatic pressing （HIP） method, using CaF2 nanopowders synthesized by chemical precipitation method as raw materials. The nanopowders and transparent ceramics were studied using X-ray diffraction, transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and spectrophotometer. The experimental results indicated that the obtained nanopowders presented normal distribution with grain size about 30 nm; transmittance of CaF2 transparent ceramics was 39% and 26% at 1100 nm for LiF and NaF as sintering addictives, respectively, with corresponding mean grain size 188 μm and 44 μm. Loss of transmission could be attributed to the residual closed porosity. Sintering mechanism was liquid-phase sintering at pre-stage, then solid-phase sintering at later stage, as well as solid solution of lithium ions and sodium ions in the CaF2 lattice structure.
Calcium fluoride nanoparticles with various amounts of erbium ion dopants were prepared by CTAB/C_4 H_9OH/C_7H_(16)/H_2O reverse micro-emulsion method.The nanoparticles were studied by X-ray diffraction(XRD),transmission electron microscopy(TEM),fourier transform infrared spectroscopy(FTIR),absorption and fluorescence spectra.The XRD patterns indicate a typical cubic fluorite structure and no other impurities.TEM results show the synthesized particles having uniform grain size and without agglomeration.FTIR spectra reveal that there are some amounts of-OH,NO_3^-and other organic functional groups on the particle surfaces before the annealing process.Many absorption peaks and bands are present in the absorption spectra,corresponding to the rich energy levels of erbium ion.The Red-Shift of absorption bands and Blue-Shift of fluorescence peaks can be attributed to the weakened energy level split as a result of the decrease in crystal field strength.
