Fabrication And Optical Properties Of Er:SrF₂ Transparent Ceramics

Due to the well air permeability,overlap with strong water absorption sites and high absorption of water,the mid-infrared lasers have the potential applications in remote sensing,medicine,communications and spectrum detection.The transition from energy level ⁴I_11/2 to ⁴I_13/2 of Er³⁺will produces the light with the wavelength ranged from 2.6-3?m.Because of the lifetime of the lower level is larger than that of the higher level,the laser matrix material needs to have the small phonon energy to realize the mid-infrared laser.Compared with the phonons energy of the oxides and CaF₂,the SrF₂ has the smaller phonons energy,higher thermal conductivity and negative thermal optical coefficient.In particularly,the negative thermal optical coefficient can compensate the thermal lens effect in the process of the laser oscillation.Furthermore,compared with single crystal,the ceramics have the excellent mechanical properties and can realize the ions doping with higher concentration.Therefore,the SrF₂transparent ceramics are the potential good mid-infrared laser matrix materials.At present,the deformation of the single crystal and powder densification are the main methods to fabricate the SrF₂ transparent ceramics.Among them,the higher optical quality de poly crystal SrF₂ can be obtained through single crystal thermal deformation,but the problems existed in the grow process of the single crystals still exist.For the powder densification method,the SrF₂ transparent ceramics were also fabricated successful.However,the investigation on the microstructure evolution and sintering behavior in the densification process of the SrF₂ powder are so rare in the references.For this reason,the thesis is focusing on the synthesis of the SrF₂ powder and the optimization of the sintering technology of the SrF₂ transparent ceramic.The SrF₂ powders were synthesized by precipitation,and the powders were densified by vacuum hot pressing sintering.The high optical quality SrF₂ transparent ceramics were fabricated by controlling the synthesized parameters of the powder and the hot pressing sintering parameters.The densification mechanism of the Sr F₂ transparent ceramics were clarified by investigating the microstructure evolution of the SrF₂ ceramics under different sintering parameters.The researches in the thesis are as follows:1.The synthesis of the Sr F₂ powder by chemical precipitation methodThe SrF₂ nano-powders were synthesized by chemical precipitation,the synthesized parameters,such as fluoride sources,titration rate,aging time and doping concentration of Er³⁺,were studied systematically.The morphology of the powders were obtained by SEM,and the phase composition of the powders were recorded by XRD.The different powders were densified under the same sintering conditions.The effect of the synthesized parameter of the powder on the in-line transmittance of the samples were investigated.The results showed that the SrF₂ transparent ceramics fabricated using the KF as the fluoride sources have the better optical transmittance.Furthermore,the SrF₂ powder with size of 50 nm possess the well dispersity can be synthesized when the titration rate was 2.5 ml/min,aging time was 20 h and doping concentration of Er³⁺was 5 at.%.2.The densification of the SrF₂ powderThe SrF₂ powder were synthesized by the optimized powder synthesis technology.The SrF₂ powder were densified through sintering by hot pressing.The relative density of the sintered samples were got by the Archimedes method.The microstructure of the sintered ceramics were obtained by SEM,and the phase composition of the sintered ceramics were recorded by XRD.The in-line transmittance of the ceramics samples were carried out by UV-Visible.The effect of the sintering temperature,heating rate and holding time on the microstructure evolution and densification degree of SrF₂ceramics were investigated systemically.The results showed that the optimized sintering parameter is the heating rate of 1°C/min,the sintering temperature of 700°C and the holding time of 40 h.The transmittance of SrF₂ transparent ceramics fabricated under this sintering parameter can reach 92%at 2000 nm.The grain growth mechanism was clarified by the investigating of the microstructure evolution.It showed that the lattice diffusion is the grain growth mechanism in the SrF₂ ceramics.Furthermore,the emission spectrum of the Er³⁺doped SrF₂ transparent ceramics was recorded under the excitation of 975 nm.The results showed that the strongest emission peak located 2735nm,which meant the laser round 2.7 nm can be realized in the SrF₂ transparent ceramics.