Preparation And Luminescence Properties Of Rare Earth Doped SiO₂-B₂O₃-TiO₂-Y₂O₃ System Glass Ceramics

The up-conversion luminescent material emits visible light under infrared excitation（980 nm）,so it has a wide range of applications in biomonitoring,lighting,printing and other fields.Titanate glass ceramics have titanate crystalline phases uniformly distributed in the oxide glass network,which not only have high chemical stability and mechanical strength of oxide glass ceramics,but also have high luminescence intensity in titanate matrix.Titanate glass ceramics is one of the excellent matrix materials for rare earth ion upconversion luminescence.In this thesis,Er³⁺-Yb³⁺、Ho³⁺-Yb³⁺and Tb³⁺-Yb³⁺doped transparent glass ceramics containing Y₂Ti₂O₇crystal phase were prepared by the melting crystallization method,respectively.By discussing the effects of heat treatment time and temperature on the crystallinity,average grain size and light transmittance of glass ceramic samples,the optimal heat treatment conditions for Er³⁺-Yb³⁺、Ho³⁺-Yb³⁺and Tb³⁺-Yb³⁺co-doped with Y₂Ti₂O₇crystalline phase were determined as follows:690℃/2 h,730℃/2 h and 720℃/2 h,respectively.According to up-conversion emission spectra,the Judd-Ofelt theory,and the Eu³⁺ion as a fluorescent probe is used to explain the higher luminescence intensity of the glass ceramics than the precursor glass.The optimum doping concentrations of Er³⁺-Yb³⁺and Tb³⁺-Yb³⁺are determined to be0.5%-0.9%and 0.4%-0.7%,respectively,and the optimum doping concentrations of Ho₂O₃-Yb₂O₃are 0.3%and 0.6%by up-conversion emission spectra.According to the relationship between pump power and emission intensity,the up-conversion processes of Er³⁺-Yb³⁺,Ho³⁺-Yb³⁺and Tb³⁺-Yb³⁺are all two-photon processes.According to CIE chromaticity coordinates,the chromaticity coordinates of all glass ceramics are in the green light region.Using Ge O₂instead of SiO₂in the 0.3%Ho₂O₃-0.6%Yb₂O₃doped glass ceramics,with the increase of Ge O₂,the Vickers hardness gradually decreases,while the up-conversion luminescence intensity gradually increases.The up-conversion green light emission at 980nm excitation was enhanced about 4.48 times by adding Li⁺ions in 0.4%Tb³⁺-0.7%Yb³⁺doped glass ceramics.According to the variable temperature fluorescence spectra,the maximum absolute and relative sensitivities of 8%Li⁺-0.4%Tb³⁺-0.7%Yb³⁺doped glass ceramics containing Y₂Ti₂O₇crystal phase are 0.97×10^-2K^-1and 0.91%K^-1,respectively.The quantitative relationship between the three-dimensional structural parameters and the light transmittance of glass ceramics containing Y₂Ti₂O₇crystal phase is investigated by stereology principle.The results show that the light transmittance increases with the increase of the three-dimensional free distance（λ）or the average specific surface area(S_VP)of a single grain.While the surface area（S_V）per unit volume or the spherical diameter(D_3S)increases,the light transmittance decrease.Therefore,controlling the distance between grains,the radius and shape of grains can improve the light transmission of glass ceramics.The microstructures of Er³⁺-Yb³⁺,Ho³⁺-Yb³⁺,and Tb³⁺-Yb³⁺doped glass ceramics containing Y₂Ti₂O₇crystal phase is analyzed by fractal theory.It is proved that the structure of glass ceramics has fractal characteristics.The results show that the transmittance tends to decrease as the fractal dimension of the glass ceramic samples increases.The fractal dynamics theory is applied to analyze the grain growth process of glass ceramics and establish the relationship between the dynamics parameter h and the percentage of crystal area.The dynamics parameters h of Er³⁺-Yb³⁺,Ho³⁺-Yb³⁺,and Tb³⁺-Yb³⁺doped glass ceramics containing Y₂Ti₂O₇crystal phase were obtained by linear fitting and the fractal subspectral dimensions ds were calculated as 1.9254,1.8958,and 1.8138,respectively.