UV-VUV spectroscopy of rare earth doped persistent luminescence materials

The electronic and defect energy level structure of polycrystalline SrAl2O4:Eu2+,R3+ persistent luminescence materials were studied with thermoluminescence and UV-VUV synchrotron radiation emission and excitation spectroscopy. Theoretical calculations using the density functional theory (DFT) were carried out simultaneously with the experimental work. The experimental band gap energy (Eg) value of 6.6 eV agrees very well with the DFT value of 6.4 eV. The 4f7 → 4f65d1 excitation bands of Eu2+ were found rather similar irrespective of the R3+ co-dopant. The trap level energy distribution depended strongly on the R3+ co-dopant except for the shallowest trap energy above the room temperature remaining the same, however. The different processes in the mechanism of persistent luminescence from SrAl2O4:Eu2+,R3+ was constructed and discussed.