The Study On The Microstructure And Optical Properties Of Nd³⁺,Y³⁺: CaF₂ Transparent Ceramics

The fluoride laser materials command many advantages such as wide spectra,good thermal conductivity,low refractive index and low phonon energy,so that it has been widely applied in windows materials and laser gain materials.Nd³⁺ions belong to four-level energy system,which center laser wavelength is at 1054 nm.Meanwhile,it is easy to achieve the population inversion and continuous tuning between 1000 nm and 1100 nm,so that it is very appropriated to be applied in the field of nuclear fusion energy.However,fabricating high quality transparent ceramics is very difficult.Meanwhile,the quality of the fabricated ceramics has a significant impact on the optical properties of the samples.In this paper,we successfully synthesized the Re³⁺:CaF₂ nanopowders by co-precipitation method.We fabricated the CaF₂ transparent ceramics by hot-pressed method and studied their microstructure and optical properties.The main contents of this research are as follows:The Nd³⁺:CaF₂ and Nd³⁺,Y³⁺:CaF₂ nanoparticles were synthesized by co-precipitation method.The effects of Nd³⁺ions,Y³⁺ions doped concentrations on the grain size,lattice constant and nanopowders morphology were studied,which were judged from the point of charge compensation.With the increase of Re³⁺ions doped concentrations,the grain size gets decreased and the lattice constants get increased.Meanwhile,the impact of grinding degree of on the agglomeration degree of the nanopowders was also invesitagetd.The Re³⁺:CaF₂ transparent ceramics were obtained by hot pressed method.The effects of sintering conditions such as the agglomeration degree of the nanopowders,sintering pressure,dwelling time and heating rate on the microstructure and in-line transmittance were studied.To some extent,the well dispersed nanoparticles,high pressure,long dwell time,slow heating rates are beneficial for the grain growth and pores exclusion.In addition,the effects of the Nd³⁺ions doped concentrations and the Y³⁺ions doped concentrations on the microstruture and optical propertiess of Nd³⁺:CaF₂ and Nd³⁺,Y³⁺:CaF₂ ceramics were studied.With the increase of Nd³⁺ions doped concentrations,the grain size of Nd³⁺:CaF₂ ceramic gets decreased.To some extent,doping Y³⁺ions improves the in-line transmittance of the transparent ceramics.At 1054 nm,the in-line transmittance of the 1 at.%Nd³⁺,2 at.%Y³⁺:CaF₂ ceramics reached up to 87%.The fluorescent spectra of the Nd³⁺,Y³⁺:CaF₂ nanopowders,ceramic powders and ceramics were compared in one group,which reveals that the emission intensity of the transparent ceramics is the highest among these samples.The emission properties of different optical in-line transmittance ceramics fabricated by different sintering pressure were investigated.Meanwhile,the effects of Nd³⁺ions doped concentrations and Y³⁺ions doped concentrations on the absorption and emission spectra of the CaF₂ ceramics were investigated.With the increase of Nd³⁺ions doped concentrations,the emission intensity of the Nd³⁺:CaF₂ ceramic get decreased.Doping the Y³⁺ions highly improves the emission properties of the fabricated ceramics.And the Nd³⁺cluster and cross relaxation effect were explained from the perspective of charge compensation and rare earth coordination.The ⁴F_3/2 energy level's decay time of 1 at.%Nd³⁺,2 at.%Y³⁺:CaF₂ ceramics reached up to 220.52?s.