Studying On Fabrication And Luminescence Properties Of Polycrystalline BaF₂/CaF₂ Laser Transparent Ceramics

Ba F2/Ca F2 ceramics have been widely used as optical devices and the substrate of the solid-state lasers due to their several favorable properties, such as good optical transmission, chemical stability, wide transparency range and low phonon energy. The flouorcscence decay time of the Ba F2 is 0.6ns,which is the fastest inorganic scintilator materials ever found. The Ce ions are the most fitting element doped to the base materials, because they can turn self trapped excitation luminescence into self luminescence. Both of Tm3+ and Ho3+ have special energy levels, which is beneficial to gaining the multichannel excitation luminescence by Tm3+/Ho3+ Co-doping.The 0.1%Ce3+:Ba F2 nanoparticles were synthesized by co-precipitation method and the 0.1%Ce3+:Ba F2 transparent ceramics were prepared by vacuum sintering.Nanoparticles were characterized on their lattice structure, morphology, phase composition and fluorescence by the XRD, TEM, SEM, fluorescence spectrometer,respectively. The effects of sintering temperature, holding time and cold isostatic pressing on the transparency, relative density and the fluorescence intensity of the transparent ceramics were also been studied. The morphology of the 0.1%Ce3+:Ba F2 nanoparticles exhibited approximately granular with the particle size of 200-300 nm and good dispersibility. The XRD results showed that the powders had the best crystallinity at 600℃. The maximum transparency and relative density of the0.1%Ce3+:Ba F2 transparent ceramic were 69.2% and 98.93% respectively at 1275℃for 4h. The fluorescence intensity of the 0.1%Ce3+:Ba F2 transparent ceramics enhanced with increasing the sintering temperature. The peak 290 nm belonged to the characteristics absorption of Ce3+ions. The excitation wavelength located in 610 nm and 650 nm was originated from the electron of the Ce3+ ions f-f energy level transition.The transparency and fluorescence intensity of transparent ceramics prepared by the calcination after cold isostatic pressing was higher than those of synthesized by the reverse sequence. However, the difference between fluorescence intensity decreased with decreasing the sintering temperatures. The maximum transparency and relative density of the 0.1%Ce3+:Ba F2 transparent ceramic were 71.4% and 99.24%,respectively obtained at 1275℃ for 6h. At the same time, the fluorescence intensity also reached a maximum value with the excitition peaks located at 524nm(5d1â†'2F7/2).The Ce3+:Ca F2 nano-particles were prepared by hydrothermal process and characterized on their fluorescence. The results showed that the size of nano-particles decreased with increacing the reactant concentration. The addition of PEG was beneficial to graining the refinement Ce3+:Ca F2 grain with the size of 92.06 nm when the proportion of the additive was 3wt.%. On the other hand, the size of nano-particles without the addition of PEG was 126.76 nm. The grain size synthesized at 160℃ was fine and uniform. The concentrations of the reactants, the reaction temperature and holding time had few effects on fluorescence intensity of the Ce3+:Ca F2 ceramics. The limit doping amount of Ce3+ was 1% and with increasing the doping amount the lattice constant increased first, and then decreased. The absorption peak belonged to the characteristics absorption of Ce3+ ions and the excitation peaks was located at 620nm(2F5/2â†'2F7/2).The Tm3+/Ho3+:Ba F2 nano-powders were prepared by co-precipitation. The results showed that both of the maximum doping concentration of Tm3+ and Ho3+ in Ba F2 matrix were 0.3%. The maximum fluorescence intensity of the nano-powders after calcining was gained at 800℃. In this study, the Tm3+/Ho3+:Ba F2 transparent ceramics were prepared by the vacuum sintering, in which the cold isostatic pressing was carried out before calcining, and the ceramics were sintered at 1275℃ for 6h. The maximum transparency of transparent ceramic samples was 70.3%. The fluorescence results showed that the excitation peaks was located at 526nm(Tm3+, 1G4â†'3H5),586nm(Ho3+, 5F4/5S2â†'5I8) and 624nm(Ho3+, 5F5â†'5I8).