Preparation And Spectroscopic Properties Of Nd³⁺,La³⁺:CaF₂ Transparent Ceramics

With the continuous deepening of laser technology in national defense,medical and industrial applications,materials selection and preparation for laser medium have aroused great interests.Compared with single crystal and glass,transparent ceramic becomes the important research direction of solid laser materials because of its comprehensive excellent properties.The rare earth ions doped CaF₂ ceramic is a promising solid laser material due to its excellect properties such as the low phonon energy,high transmittance,rich vancancy structure to facilitate doping.Nd³⁺ions have abundant energy level structures due to three isolated parallel electrons in 4f orbit,and it has light emission from ultraviolet to infrared wavelengths.However,single doped Nd³⁺:CaF₂ transparent ceramic has low quantum efficiency due to its serious fluorescence quenching effect.In order to solve the problem,La³⁺ions are added to break the cluster and improve the fluorescence spectrum performance.In this paper,the Nd³⁺,La³⁺:CaF₂ nanopowders were prepared by chemical precipitation method.The effects of technological parameters?titration rate and rare earth ion content?on the phase composition,particle size and cell parameters of powder were studied.The Nd³⁺,La³⁺:CaF₂ ceramics were fabricated by hot-pressed method using the as-prepared nanoparticles as raw materials and study the effects of sintering temperature and concentrations of rare earth ions on the optical properties and microstructure.The Nd³⁺,Y³⁺:CaF₂ ceramics were prepared at the same concentrations and discuss the effects of different buffer ions Y³⁺and La³⁺on the fluorescence properties of Nd³⁺:CaF₂ ceramics.The contents of the study are as follows:1.The Nd³⁺,La³⁺:CaF₂ nanopowders were obtained using chemical precipitation method.It was found that the actual doping concentration of rare earth is closer to the theoretical doping concentration at slow speed.In addition,Nd³⁺ions and La³⁺ions interfere with each other's incorporation into the CaF₂ lattice.Codoping with high concentration of La³⁺ions would lead to the second phase of LaF₃.Under the environment of low concentration of La³⁺ions,the particle sizes of nanopowder decreased from 23.63 nm to 19.07 nm and the lattice parameter increased from 5.466?to 5.493?with the increase of La³⁺ions from 0 at.%to 7 at.%.2.The Nd³⁺,La³⁺:CaF₂ ceramics were fabricated by hot-pressed method.It was found that the optical transmittance and relative density of ceramics were the best at700?,the transmittance was 88.16%at 1200 nm and the relative density was 99.5%.Besides,the effects of concentrations of La³⁺ions on the structure and transmittance of Nd³⁺:CaF₂ transparent ceramics were also studied.The ceramic has the highest transmittance when the La³⁺ions reached to 1 at.%.With the increase of La³⁺ions,the grain size of Nd,La:CaF₂ ceramics decreased.The proper concentration of La³⁺ions can promote the process of ceramic sintering.Too much La³⁺ions reduced the quality of ceramic because of the high speed of grain boundary wrapping the bubbles.3.The emission properties of 1 at.%Nd³⁺:CaF₂ transparent ceramics with different concentrations of La³⁺ions or Y³⁺ions were investigated.It was found that the intensity of the fluorescence spectrum was greatly enhanced with the increase of buffer ions(La³⁺,Y³⁺).The newly generated emission peak at 1050 nm changes significantly with the increase of La³⁺ions which was attributed to the new[Nd³⁺-La³⁺]clusters on the emission spectra of Nd³⁺,La³⁺:CaF₂ transparent ceramics.The similar phenomenon happened in the Nd³⁺,Y³⁺:CaF₂ transparent ceramics.The emission peak at 1054 nm was attributed to the new[Nd³⁺-Y³⁺]clusters.Compared with Nd³⁺,Y³⁺:CaF₂ ceramics,Nd³⁺,La³⁺:CaF₂ ceramics have longer luminescence lifetime due to the larger radius of La³⁺ions at the same doping concentration.Codoping with La³⁺ions could better increase the average distance of Nd³⁺ions which can effectively reduce the cross-relaxation effect and increase the fluorescence lifetime of Nd³⁺:CaF₂ transparent ceramics.