Synchrotron radiation investigations of the Sr 2MgSi 2O 7:Eu 2+,R 3+ persistent luminescence materials

Abstract

The electronic and defect energy level structure of polycrystalline Sr 2MgSi 2O 7:Eu 2+,R 3+ persistent luminescence materials were studied with thermoluminescence and different synchrotron radiation spectroscopies (UV-VUV emission and excitation, X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS)). Special attention was paid on the effect of the R 3+ co-dopants on the persistent luminescence properties of the materials. Theoretical calculations using the density functional theory (DFT) were carried out simultaneously with the experimental work. The experimental band gap energy ( E g) value of ca. 7.1 eV agreed very well with the DFT value of 6.7 eV. The variation of the E g value was attempted to relate with the trap structure as well as with the different properties of the R 3+ co-dopants. The trap level energy distribution depended strongly on the R 3+ co-dopant except for the shallowest trap energy above the room temperature remaining practically the same, however. The different processes in the mechanism of persistent luminescence from Sr 2MgSi 2O 7:Eu 2+,R 3+ were assembled and their contributions discussed.