Crystal structure of Na_2MMgP_2O_8 (M: Ba, Sr, Ca) orthophosphates and their luminescence properties activated by Eu _2; Analogous structural behaviors of glaserite-type phosphates and silicates

摘要

Rietveld refinements of X-ray powder diffraction data and vibrational spectroscopy have confirmed the crystal structure of Na_2MMgP _2O_8 (M: Ba, Sr, Ca) prepared by a standard solid state reaction. They have glaserite-type layered structure. Na_2MMgP _2O_8 has a trigonal P3 form for M=Ba, and monoclinic P2_1/c forms for M=Sr and Ca. The observed structural transition is analogous to the corresponding layered orthosilicate M_3MgSi _2O8. Eu_2-doped Na_2MMgP _2O_8 exhibits an intense blue to violet emission under ultraviolet excitation, based on 5d4f electron transition of Eu_2 ions. The emission character is very sensitive to the structural transition induced by M_2 and the subsequent site symmetry changes.