Luminescence properties of Eu2+ in M2MgSi2O7 (M = Ca, Sr, and Ba) phosphors

The photoluminescence properties of alkali-earth magnesium silicates (M2MgSi2O7, M = Ca, Sr, and Ba) doped with Eu2+ were investigated. Solid solutions of BaxSr2-xSi2O7, Ca2MgSi2O7, and Sr2MgSi2O7 were prepared. BaxSr2-xSi2O7 retained a tetragonal crystal structure similar to the structure of the other compounds up to a stoichiometry of x = 1.6, which enabled a systematic study of the common structure. Monoclinic Ba2MgSi2O7 was prepared, and the luminescence properties were compared with those of other samples. The emission and excitation spectra of tetragonal M2MgSi2O7 (M = Ca, Sr, and Ba) changed as a function of the covalency, site symmetry, and crystal field strength. The luminescence properties showed excellent agreement with theoretical predictions based on these factors. The Stokes shift differentiated the emission behaviors of the tetragonal and monoclinic structures.