Preparation And Up-conversion Luminescence Properties Of Ho³⁺/Tm³⁺/Yb³⁺ Doped Transparent Glass Ceramics Containing Sr₃Gd（PO₄）₃

Up-conversion luminescence materials are able to emit visible light under near-infrared excitation,which is widely used in in lighting,biological monitoring,precision machining,printing and other fields.A series of Ho³⁺doped,Ho³⁺/Yb³⁺co-doped and Ho³⁺/Tm³⁺/Yb³⁺tri-doped transparent glass ceramics containing Sr₃Gd（PO₄）₃ were prepared by melting-crystallization method.The crystal phase of the prepared glass ceramics is Sr₃Gd（PO₄）₃ by comparing the X-ray diffraction data with the standard card.The microscopic morphology,grains distribution and grains size in glass ceramics are observed by scanning electron microscope（SEM）.Combined with the analysis results of differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,SEM and light transmittance,the optimum heat treatment conditions for Ho³⁺doped,Ho³⁺/Yb³⁺co-doped and Ho³⁺/Tm³⁺/Yb³⁺tri-doped precursor glasses are determined to be 760℃/140 min,780℃/3 h and 770℃/2.5 h,respectively.Comparing the Vickers hardness,density and chemical stability of precursor glass and glass ceramics,and the reasons of the increase of hardness,density and acid-alkali resistance of glass ceramics after heat treatment are analyzed.Up-conversion emission spectra of Ho³⁺/Tm³⁺/Yb³⁺doped glass ceramics with different concentrations are analyzed to determine the optimum doping concentration of rare earth ions,and obtained the cause of the concentration quenching by calculating the critical distance.CIE chromaticity coordinate software is used to determine the chromatics coordinate of glass ceramics,which more directly shows the change trend of up-conversion luminescence color of glass ceramic,and it is found that the tunable up-conversion emission from green to white can be realized by adjusting the concentration of different rare earth ions.When doped with 0.3%Ho₂O₃-0.8%Yb₂O₃,the green up-conversion luminescence intensity of the glass ceramic is the strongest.When doped with0.1%Ho₂O₃-0.2%Tm₂O₃-0.8%Yb₂O₃,the glass ceramic can produce white light emission,and the corresponding color coordinates are（0.3384,0.3309）,which is the closest to the standard white light.The up-conversion emission processes of Ho³⁺and Tm³⁺are determined to be two-photon processes according to the relationship between pump power and luminescence intensity,and the energy transfer mode among Ho³⁺,Tm³⁺and Yb³⁺is shown by the schematic diagram of up-conversion luminescence process.The results indicate that Ho³⁺/Tm³⁺/Yb³⁺doped transparent glass ceramics containing Sr₃Gd（PO₄）₃have wide application prospect in the field of safety channel signage,solid-state lighting,medical treatment and so on.