Crystal structure of Na2MMgP2O8 (M: Ba, Sr, Ca) orthophosphates and their luminescence properties activated by Eu2+; analogous structural behaviors of glaserite-type phosphates and silicates

Rietveld refinements of X-ray powder diffraction data and vibrational spectroscopy have confirmed the crystal structure of Na2MMgP2O8 (M: Ba, Sr, Ca) prepared by a standard solid state reaction. They have glaserite-type layered structure. Na2MMgP2O8 has a trigonal P3̄ form for M=Ba, and monoclinic P21/c forms for M=Sr and Ca. The observed structural transition is analogous to the corresponding layered orthosilicate M3MgSi2O8. Eu2+-doped Na2MMgP2O8 exhibits an intense blue to violet emission under ultraviolet excitation, based on 5d–4f electron transition of Eu2+ ions. The emission character is very sensitive to the structural transition induced by M2+ and the subsequent site symmetry changes.