Electronic structure of defects in Sr2MgSi2O7:Eu2+,La3+ persistent luminescence material

The modifications in the crystal and electronic structure due to the introduction of strontium and oxygen vacancies in the Sr2MgSi2O7 persistent luminescence host material were calculated using the density functional theory (DFT). The defect energy level structures of the Sr2MgSi2O7:Eu2+(,La3+) materials were studied with the thermoluminescence (TL) spectroscopy, as well. Both shallow and deep electron traps due to isolated oxygen and strontium vacancies and hole traps due to an isolated strontium vacancy were located in the energy gap (Eg) of the host. The shallow electron traps can contribute to persistent luminescence since they are readily bleached by the thermal energy at room temperature. The DFT calculations suggest that the strontium vacancies created by the substitution of Sr2+ with R3+ have a significant role in the creation of electron traps highly useful in promoting persistent luminescence as shown experimentally. The present results indicate that the differences between the calculated and experimental trap level structures may be due to the defect aggregation.