Theoretical calculations and investigation on properties and defect states in SrMgGe2O6: Mn2+, Sm3+

This paper realizes a new red long-wavelength afterglow material SrMgGe2O6(SMGO): Mn2+, Sm3+, with emission peaks distributed from 600 nm to 850 nm. Different from the previous experimental approach of trial-and-error, this work starts with the first principle and tries to predict the properties of SMGO: Mn2+, Sm3+ and instruct the actual synthesis utilizing theoretical calculations. Firstly, it is determined that Mn2+ energy level is suitable for the luminescence energy level, while Sm3+ is more suitable for the trap energy level by calculating the possible defect energy level positions of the two doped ions and combining with Dorenbos theory; meanwhile, the formation energy of all possible defects is listed and computed, thus corresponding to the source of each trap. In addition, the Mulliken population was introduced to make a more accurate prediction of the photoluminescence of Mn2+. The experimental results match the predictions very well, as the Mn2+ single-doped material exhibits red afterglow emission, while the initial intensity of the afterglow of the Sm3+ co-doped is increased by about 1.4 times and the duration is increased by about 39 times. Finally, a feasible afterglow mechanism is proposed and cryptographically relevant applications are designed and achieved according to the different performances of the materials with single doping and co-doping.