Regulating Oxygen Defects And Upconversion Fluorescence Of Ba₂ScAlO₅:Yb³⁺/Ho³⁺ Via Vacuum Annealing

Upconversion materials doped with rare earth has great application potential in the solar cell,non-contact temperature measurement,medical treatment and biological imaging and other fields.There are many factors that can influence on the conversion efficiency,such as the host materials,the type and concentration of doped with rare earth ions,material microstructure and defects,etc.Our group successfully preparedβ-Ba₂ScAlO₅:Yb³⁺/Er³⁺upconversion fluorescent materials by high-temperature solid-states method in hydrogen atmosphere and showed good fluorescence,but the up-conversion fluorescence intensity decreased significantly or even quenched after annealing in air atmosphere.Based on the first principles calculation,it is proposed that the"gap oxygen"defect is the cause of the up-conversion luminescence quenching.In order to further study the effect of oxygen defects on luminescence properties of rare-earth doped withβ-Ba₂ScAlO₅ upconversion fluorescent materials,in this paper,β-Ba₂ScAlO₅:Yb³⁺/Ho³⁺upconversion fluorescent materials were prepared by high-temperature solid-states in hydrogen and air atmosphere respectively,and their upconversion luminescence properties were studied.The upconversion intensity of samples prepared in air atmosphere followed by vacuum annealing was achieved by samples prepared in hydrogen.The research results obtained in this thesis are summarized as follows:（1）Using Ba:Sc:Al:Yb:Ho=2.2:1.1–x–y:0.9:x:y（0<x<0.3,0<y<0.011）as raw material ratio,β-Ba₂ScAlO₅:Yb³⁺/Ho³⁺upconversion fluorescent material was prepared in hydrogen and air atmosphere respectively.The optimal doping concentration of rare earth ions are x=0.2,y=0.008 and x=0.15,y=0.005 respectively.The upconversion fluorescence ofβ-Ba₂ScAlO₅:Yb³⁺/Ho³⁺samples prepared in hydrogen decreased significantly to quenching after air annealing,similar to the previous Er³⁺activated samples.（2）After vacuum annealing ofβ-Ba2ScAlO5:0.15Yb³⁺,0.005Ho³⁺upconversion fluorescent materials prepared in air,the integrated intensity of green、red and near infrared increased by 39.5,128.6 and 35.2 times,respectively.The luminescence intensity ofβ-Ba₂ScAlO₅:0.15Yb³⁺,0.005Ho³⁺upconversion fluorescent materials was almost consistent with that of samples prepared in hydrogen.（3）Oxygen defect is the structural reason that affects the upconversion fluorescence ofβ-Ba₂ScAlO₅ activated by rare earth ions.Different oxygen defect content leads to different absorption of visible light in the matrix,resulting in different fluorescence intensity.XRD refinement showed that the oxygen vacancy content of the sample after vacuum annealing was 1.3%,which was 1.1%higher than that of the sample prepared in air.EPR results also showed that the oxygen vacancy content of the sample after vacuum annealing was increased.The sample prepared in air has strong absorption in the range of visible and near infrared,which makes the upconversion fluorescence of the material absorbed by the host,so the luminous efficiency is low.The absorption of samples annealing in vacuum in visible and near infrared range is low,and the luminous efficiency is greatly improved.（4）The study of the cell point defect ofβ-Ba₂ScAlO₅ reveals the reason of obtaining single-phase samples by non-stoichiometric ratio.In addition to oxygen vacancy,the sample prepared in air also has certain vacancy of metal Ba²⁺,and Sc³⁺can replace Al³⁺,which is easy to obtain Ba Al₂O₄ by sintering in the stoichiometric ratio sample.Therefore,excessive barium carbonate and scandium oxide need to be added in the raw material ratio to obtain the target product.