Luminescence and electric dipole in Eu3+ doped strontium phosphate: Effect of SiO4

Eu³⁺-doped strontium phosphorous silicate phosphors were synthesized at 200 °C using microwave-assisted reaction and their crystal structure and optical properties were investigated. Cation/anion ratio and SiO₄ content in strontium phosphorous silicate are sensitive to processing conditions such as pH and starting composition of reaction precursors. Stoichiometric Sr₅(PO₄)₂(SiO₄):Eu³⁺ phosphor prepared by the microwave reaction emits more intense red light than previously reported Sr₅(PO₄)₂(SiO₄):Eu³⁺ and Sr₅(PO₄)₃OH:Eu³⁺ phosphors. As the amount of SiO₄ in the anion site increases and P/Si ratio gets close to stoichiometry, the intensity of red luminescence with a narrow band width increases. Strong red luminescence from Sr₅(PO₄)₂(SiO₄):Eu³⁺ synthesized by the microwave-reaction is explained from the viewpoint of defect formation, charge compensation during co-doping process, and local structural symmetry. Large electric dipoles near Eu³⁺ ions enhance photoluminescence of Sr₅(PO₄)₂(SiO₄):Eu³⁺ from ⁵D₀-⁷F₂ transition at a peak wavelength of 614 nm. This study shows that Sr₅(PO₄)₂(SiO₄):Eu³⁺ prepared by the microwave reaction is promising red phosphor for white light emitting diode.