The Study On The Preparation Process And Optical Properties Of Eu³⁺:CaF₂ Transparent Fluorescent Ceramic

Since its appearance in the middle of the last century,Eu:CaF₂ transparent fluorescence ceramic materials have attracted the attention of researchers because of their unique optical properties.The optical properties of Eu:CaF₂ ceramics are derived from Eu ions.The two different valence states of Eu ions caused the difference in performance:The spectrum of Eu³⁺is derived from the f-f energy level transition of the electron.The performance does not change with the matrix and has a long fluorescence lifetime.Eu³⁺:CaF₂ ceramic is a common fluorescent material.Eu²⁺electrons are mainly occurs in the F-D level,the fluorescence lifetime is short and spectrum can be controlled at random in the range of visible light.These advantages make it can be used for radiation detection and scintillation materials.The two different properties of Eu ions have different degrees of conversion in some matrix materials,but there is little research about the reduction of valence state in the CaF₂matrix.CoMPared with the optical properties,few scholars have reported on the improvement of Eu:CaF₂ ceramics.However,in fact,the most fundamental of the optical performance is based on the properties and structure of the material itself.In this paper,Eu:CaF₂ transparent ceramic nanopowders were prepared by coprecipitation method,then Eu:CaF₂ transparent ceramics were obtained by vacuum hot pressing.The ceramics were characterized and discussed by phase analysis,quantitative analysis and spectral testing:1.After the investigation of the reaction concentration,it is found that the loss of Eu³⁺is increased with the rises of the concentration,and the agglomeration degree of the nanopowder increases,which is not conducive to the sintering;For different Eu³⁺content experiments,it is found that with the increase of doping concentration,the grain size decreases,and the cell parameters increase,the powders are slightly reunite,the CaF₂ crystallinity decreases and line defects appear;By XPS spectrum analysis,it was found that the Eu ions in the sample showed two valence states of Eu²⁺and Eu³⁺,and the content of Eu²⁺decreased with the increase of doping concentration.2.Through analysis of sintering process parameters:it is found that the sintering pressure can counteract the stress concentration on the grain surface and promote the discharge of the pores.For Eu:CaF₂ ceramics,the relatively suitable sintering pressure is 30MPa;By discuss the influence of sintering temperature:Decreasing internal defects of materials can enhance transmittance.Increasing temperature can promote densification process,increase grain size,move pores at grain boundaries,and increase material density.However,due to the high temperature of the ceramics under 700^oC,the overheating appeared.High temperature makes the abnormal growth appeard,caused the intragranular pores and other defects,which makes the density and transmittance of ceramics decreased.The suitable sintering temperature was determined to be 600^oC.3.The Eu:CaF₂ transparent ceramics with different rare-earth doping concentrations were detected by fluorescence spectroscopy.It was found that the intensity of emission peak increased with the rise of Eu³⁺content,and the symmetry structure changed due to the different lattice positions occupied by F ions,which caused the the difference of emission peak.In addition,The intensity of hypersensitive transition?⁵D₀,⁷F₂?emission change with the difference of crystal field environment,so as to obtain the location information of rare earth ions;combined with the life of fitting it can be found that the Eu³⁺lifetime reach the ms level,and with the increase of rare earth ions,the non radiative transition probability increases,resulting in the fluorescence lifetime reduced.4.Through XEL analysis it can be found that Eu²⁺have the characteristic transition due to the excitation of high-energy rays,but the intensity of emission peak decrease with the increase of Eu³⁺content.Through the coMParison of the two valence states,it can be found that the growth of Eu³⁺can also play an inhibitory role in the Eu²⁺yield.