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

The local symmetry of a Eu3+ ion has a crucial effect on its luminescence properties. In this work, we show that the red/orange ratio in the emission of Eu3+-doped MgIn2P4O14 phosphors is tunable by adjusting the Eu3+ concentrations, due to the change in the local symmetry of metal ions. The substitution of Eu3+ for In3+ lowers the distortion in the lattice of monoclinic MgIn2P4O14, and an increase in Eu3+ 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 Eu3+ in MgIn2P4O14 makes the luminescence less thermally stable than that in Mg3In4P6O24.