| Rare earth ion-activated garnet is an important luminescent material.There are different requirements for lighting and scintillation application on the wavelength,intensity,lifetime and thermal stability.The phase structure and energy band structure of rare earth ion-activated garnet will be adjusted by the cation composition changes,and the defects of garnet can be modulated by processing atmosphere and doping,and accordingly accompanied by changes in luminescence properties such as excitation and emission spectra,fluorescence lifetime,thermal stability,etc.Rare-earth ion-activated garnet materials based on these property changes have potentially important application prospects.In this paper,three new rare-earth ion-activated garnet luminescent materials,RE3（Al,Ga）5O12:Ce3+,RE3（Al,Ga）5O12:Tb3+,RE3（Al,Ga）5O12:Eu3+（RE=Gd,Lu）,were prepared by high temperature solid phase method,and X-ray powder diffraction,UV-vis diffuse reflectance spectroscopy,excitation spectra and emission spectra,variable temperature emission spectra,quantum efficiency,fluorescence decay curves,thermally stimulated luminescence spectra and X-ray excitation emission spectra were characterized,the research content is as follows:（1）The effects of cation composition changes on the phases and luminescence properties of RE3（Al,Ga）5O12:Ce3+,RE3（Al,Ga）5O12:Tb3+,RE3（Al,Ga）5O12:Eu3+（RE:Gd,Lu）were investigated.It is found that Lu with smaller ionic radius than Gd is favorable to stabilize the garnet phase;Ga move into the oxygen tetrahedron can reduce the oxygen dodecahedron distortion rate,as a result,help Gd to move into the dodecahedron,which is favorable to stabilize the garnet phase.In the(GdxLu0.99-xCe0.01)3(Al1-yGay)5O12system,when Al/Ga is certain,with the increase of Gd composition,the 4f-5d2leap excitation peak of Ce3+is blue-shifted,while the4f-5d1 leap excitation peak and emission peak are red-shifted;when the Gd/Lu ratio is constant,with the increase of Ga composition,the 4f-5d2leap excitation peak is red-shifted,while the 4f-5d1 leap excitation and emission peaks are blue-shifted.In（Gd1-x Tbx）3（Al1-y Gay）5O12 and（Gd0.66Lu0.33Eu0.01）3（Al1-y Gay）5O12 garnet system,the characteristic excitation and emission peak of Tb3+,Eu3+ions are unchanged with the Ga composition increasing;in(Gd1-xTbx)3(Al1-yGay)5O12garnet system,the thermal quenching temperature energy decreases with the Ga composition increasing,and the highest quantum efficiency of(Gd0.9Tb0.1)3(Al1-yGay)5O12is 87.72%when y=0.4.For(Gd0.66Lu0.33Eu0.01)3（）Al1-yGay5O12,the quantum efficiency is 60-70%when y=0.2-0.8.（2）The effect of calcination atmosphere on the luminescence properties of((Gd0.67Lu0.33)0.995Ce0.005)3(Al0.4Ga0.6)5O12 was investigated.Calcination under oxygen atmosphere helps to suppress the generation of oxygen vacancies and shorten the fluorescence lifetime,while calcination and heat treatment under reducing atmosphere are favorable to the reduction of Ce4+to Ce3+ions and the corresponding generation of oxygen vacancies;the luminescence intensity for specimen calcined in reducing atmosphere is stronger and the fluorescence lifetime is longer than that calcined under oxidizing atmosphere,and an obvious afterglow phenomenon appears in specimen calcined under reducing atmosphere.The thermal quenching of fluorescence contains two mechanisms:ionization quenching,cross relaxation quenching.The activation energy of thermal quenching of samples calcined in different atmosphere is related to the concentration of Ce4+ions in the specimens and is not a constant value.Calcined in O2,2%O2+98%Ar,2%H2+98%Ar,the activation energy of thermal quenching of samples is 0.2777,0.3868,0.5319 e V respectively,the calcination in reducing atmosphere is beneficial to improve the fluorescence thermal stability.（3）The effect of F-co-doping on the phase and luminescence properties of RE3（Al,Ga）5O12:Ce3+was investigated,and a method to modulate the luminescence properties of Ce3+-activated garnet using anionic F-co-doping was proposed.It was found that the F-ions in(Gd0.99Ce0.01)3(Al0.4Ga0.6)5O12with F/Ce（mol）=1 increased the volume of oxygen tetrahedra and decreased the distortion of oxygen dodecahedra.the F-co-doping could adjust the valence state of Ce activated ions in phosphor and the concentration of oxygen vacancies.With the increase of F/Ce（mol）,the fluorescence intensity of the specimen and its quantum efficiency and fluorescence lifetime both increase at first and then decrease.When F/Ce（mol）=1 in F-co-doping（Gd0.99Ce0.01）3（Al0.4Ga0.6）5O12,and F/Ce（mol）=2 in the F-co-doping(Gd0.66Lu0.33Ce0.01)3(Al0.4Ga0.6),the corresponding sample have the strongest fluorescence intensity,the highest quantum efficiency and the largest fluorescence lifetime.The F-co-doping affected the fluorescence thermal stability of the specimens,the highest thermal quenching activation energy for(Gd0.99Ce0.01)3（）Al0.4Ga0.65O12(F/Ce（mol）=1)and(Gd0.66Lu0.33Ce0.01)3（）Al0.4Ga0.65O12(F/Ce（mol）=2)is 0.4685e V,0.3737 e V respectively,which significantly improves the high temperature fluorescence performance.F-co-doping concentration with the F/Ce（mol）below 0.5and above 2 reduces the characteristic spectral intensity and the luminescence lifetime of the phosphor.This study provides a new idea for anion-modulated GGAG:Ce3+scintillation materials. |
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