Study On Purification And Sintering Properties Of Nd³⁺,Y³⁺:CaF₂ Nanoparticles

The novel properties of nanocrystalline materials,especially its applications as optical materials,made them current research focus.CaF₂ transparent ceramics,especially rare earth doped CaF₂ transparent ceramics,which can be used as laser medium,generally show extended properties,such as larger doping concentration with controllable distribution in the material volume,larger size,good mechanical and thermal properties.Among the trivalent lanthanide ions,the up conversion mechanism of Nd³⁺ions has been extensively studied in various kinds of host materials.Nd-doped CaF₂ transparent ceramics have a relatively large emission cross section and a long upper level lifetime which are beneficial to obtain the high power pulses.Nd³⁺-doped CaF₂ as a laser system has been abandoned because of a very detrimental concentration quenching effect which results from the clustering of the Nd³⁺ions.Codoping with Y³⁺ions can reduce the fluorescence concentration quenching on a ccount of the formation of new[Nd³⁺-Y³⁺]clusters.Nd³⁺,Y³⁺:CaF₂ceramics were obtained by hot pressing method using Nd³⁺,Y³⁺:CaF₂ nanoparticles as raw material.In this paper,Nd³⁺,Y³⁺:CaF₂ nanoparticles were obtained using direct precipitation method.Then the effect of calcination treatment on the sintering activity of powders and the quality of ceramics were mainly explored.The mainly points of this work were summarized as follows:1.The Nd³⁺,Y³⁺:CaF₂ nanopowders were obtained by direct precipitation method.The effects of calcination temperature on the sintering properties of the obtained nanoparticles were studied by XRD?SEM?FTIR and emission spectroscopy method.The results showed that the size and surface impurity of the powder changed little under the calcination temperature of 200?.Increasing the calcination temperature to 400?,the size of the powder was obviously larger.The boundary of the particle is clear and the surface impurity is removed thoroughly.Increasing the calcination to 500?,the impurity content did not change anymore.Considering the particle size and impurity content of the powders,400?was the optimum calcination temperature.2.The effect of calcination time on the sintering activity of the powder was studied at the optimum calcination temperature of 400?.XRD?SEM and FTIR results showed that the particle size of the nanoparticle has a certain degree of growth with the increase of calcination time.The influence of calcination time on the powders is less than the that of the calcination temperature.The impurities in the powders were basically removed when the powder was calcined for 1.5 h.Considering the sintering activity of the powder and Energy-saving,the best calcination time of the nanoparticles is 1.5 h.3.Nd³⁺,Y³⁺:CaF₂ transparent ceramic were prepared by hot pressed method.The influence of calcination temperature on the properties of Nd³⁺,Y³⁺:CaF₂ ceramic were studied by testing the microstructures and transmittance of Nd³⁺,Y³⁺:CaF₂ceramics calcined different calcination temperatures.The results showed that the prepared ceramic was compact and the grain size distribution was uniform at the calcination temperature of 400?.When the calcination temperature was lower than400?,the impurity did not remove completely.When the calcination temperature was higher than 400?,the size of the nanoparticle was too large with“sintering neck”.All of the above could hinder the densification process of the ceramic.Therefore,the optimum calcination temperature is 400°C.4.Nd³⁺,Y³⁺:CaF₂ transparent ceramic were prepared by hot pressed method.The influences of sintering temperature on the microstructure and optical properties of the ceramics were studied.Higher sintering temperature could lead to burned phenomenon for the ceramic.Lower sintering temperature could lead to a worse densification process.It was confirmed that 800?was the optimum sintering temperature.