Tuning of Emission by Eu3+ Concentration in a Pyrophosphate: the Effect of Local Symmetry

The local symmetry of a Eu 3+ ion has a crucial effect on its luminescence properties. In this work, we show that the red/orange ratio in the emission of Eu 3+ -doped MgIn 2 P 4 O 14 phosphors is tunable by adjusting the Eu 3+ concentrations, due to the change in the local symmetry of metal ions. The substitution of Eu 3+ for In 3+ lowers the distortion in the lattice of monoclinic MgIn 2 P 4 O 14, and an increase in Eu 3+ doping concentration causes the metal ion sites to shift closer to an inverse center, leading to a reversal of the relative emission intensity of a magnetic dipole transition to an electric dipole transition. Meanwhile, the higher asymmetry of metal ion sites occupied by Eu 3+ in MgIn 2 P 4 O 14 makes the luminescence less thermally stable than that in Mg 3 In 4 P 6 O 24 .