Design,Fabrication And Property Of Eu-activated Alkaline Earth Orthosilicate Luminescent Materials

The Eu-activated alkaline earth orthosilicate phosphors were synthesized by high temperature solid-state reaction.The matrix crystal structure was adjusted by composition and the calcination temperature,so as to make suitable luminescence properties.The influence of cation substitution on phase composition,Eu ion valence state,Eu²⁺site preference and luminescence properties were systematically studied.The relationship among component-structure-luminescence performance was then established.The work provides a theoretical basis for qualitative/quantitative luminescence control ling.（1）(Mg_1-x-yBa_xSr_y)_1.95SiO₄:0.05Eu phosphors were synthesized at different calcination temperature.The influences of composition and temperature on the phase components and luminescence performances were explored.The phase components are gradually changed as the composition changing,and there is a Ba₂SiO₄-phase region.As the calcination temperature increases,the green phosphor component region extends and all the phosphors’brightness increases.The brightest phosphor should be the one who has the highest solid solubility.（2）(Me1_1-xMe2_x)_1.95SiO₄:0.05Eu（Me1,Me2=Ba,Sr,Mg,Ca）phosphors were also synthesized to explore equivalent cation substitution effect.Cation substitution could extend temperature rang of high-temperature phase in the single-phase region.Eu²⁺and Eu³⁺always coexist in alkaline earth orthosilicate matrix.Equivalent cation substitution with a small radius in Ba₂SiO₄ can promote Eu²⁺to be Eu²⁺（Ⅰ）,which has a larger coordination space and higher luminescence efficiency.Furthermore,equivalent cation substitution also improves luminescence thermal stability.The higher solid solubility,the better luminescence properties are.（3）Lu³⁺doped Ba_1.95SiO₄:0.05Eu phosphor was synthesized too.Unequivalent cation substitution effects were disscussed then.Lu³⁺dopant could improve the Ba₂SiO₄ phase crystal rigidity,which promotes the self-reduction reaction as Eu³⁺→Eu²⁺.It leads to the green luminescence intensity and thermal stability promotion.（4）First-principle calculations were done to study the crystal structure and electronic structure of Ba₂SiO₄:Eu²⁺.Eu²⁺site preference,energy level and related luminescence performance have been studied in details.Mg²⁺substitution effect was also investigated.Eu²⁺prefers as Eu²⁺（Ⅰ）in Ba₂SiO₄ crystal,which has a shorter green emission wavelength and poorer thermal stability than Eu²⁺（Ⅱ）.Mg²⁺substitution makes the system volume shrinking,E_g smaller,and Eu²⁺E_d-f smaller.Furthermore,Mg²⁺prefer Mg（Ⅱ）substitution.Furthermore,it has less effects on Eu²⁺（Ⅰ）than Mg²⁺（Ⅰ）.